JP2011200866A - Method and device for quenching steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a pressed product having strength difference without using welding like a tailored blank method.SOLUTION: By emitting an electromagnetic wave to the first region X of a steel sheet 1 and also emitting a stronger electromagnetic wave to the second region Y of the steel sheet 1, the second region Y is heated to 950°C which is not lower than the transformation point of the steel sheet 1 and the second region Y is made into a state of austenitic structure. By rapidly cooling the steel sheet 1 by pressing the steel sheet 1 with a press forming apparatus 10 after emitting the electromagnetic wave, the second region Y is changed into the state of a martensitic structure from the state of the austenitic structure. In this way, the strength of the second region Y is raised as compared with the first region X.

Description

  The present invention relates to a method of partially quenching a steel sheet and a steel sheet quenching apparatus that are used for manufacturing a pressed product such as a body of an automobile.

  Conventionally, press products for automobiles have been manufactured by the following procedure. First, a large sheet of steel is first cut into a predetermined shape by a mold to form a steel plate having a predetermined size called a blank. There are blanks having various sizes, various thicknesses, and various strengths. Next, various blanks were press-molded, and then each press part was assembled by welding or the like to obtain a pressed product having a structure integrated.

  However, the number of parts constituting the automobile body has reached several hundreds, and in the manufacturing procedure as described above, productivity is poor and management of parts and the like has become complicated. Therefore, a plurality of blanks having different thicknesses and strengths are butted together and the butted portions are welded together by laser welding or the like to form a press material, that is, a tailored blank, and then the tailored blank is press-molded by a press molding apparatus. The technology of manufacturing press products has become widespread.

  FIG. 3 is a diagram illustrating an example of the tailored blank 30. As shown in the figure, the first blank 31 having a low strength and a thin first blank 31 and the second blank 32 having a high strength and a thick thickness are welded together at a butt portion and integrated by a weld portion 33.

  According to such a tailored blank method, the strength of each part of the pressed product can be arbitrarily set according to the purpose. For example, in the example of FIG. 3, the first blank 31 is used for a portion that does not require strength while securing the necessary strength by using the second blank 32 for a portion that requires strength. Such a tailored blank method is described in Patent Document 1.

JP 2000-197969 A

  However, when manufacturing a press product having a difference in strength, the tailored blank method has the following problems.

  First, since a tailored blank is formed by welding a plurality of blanks, the number of components (blanks) increases.

  Secondly, there is a problem that a plurality of blanks are butted and the butt portion is welded by laser welding or the like, and the cost is high accordingly.

  Third, since blanks having different thicknesses are welded, there is a problem that the structure of a mold used for press molding is complicated.

  The method for quenching a steel plate according to the present invention irradiates the surface of the first region of the steel plate with an electromagnetic wave having a first strength, and the surface of the second region of the steel plate is larger than the first strength. A first step of heating the second region to a temperature equal to or higher than the transformation point of the steel sheet by irradiating an electromagnetic wave having a strength of 2, and by rapidly cooling the steel sheet after the irradiation of the electromagnetic wave, And a second step of changing the second region into a martensitic structure, wherein the strength of the second region is higher than that of the first region.

Further, the steel sheet quenching apparatus of the present invention can be freely inserted and removed between a press molding apparatus having an upper mold and a lower mold and between the upper mold and the lower mold, and the output can be controlled respectively. An electromagnetic wave heater having first and second heater blocks.
In a state where the electromagnetic wave heater is inserted between the upper mold and the lower mold, the electromagnetic wave heater irradiates the steel plate with electromagnetic waves, and then moves the electromagnetic wave heater to the outside of the press molding apparatus. The steel plate is sandwiched between the upper die and the lower die and press-molded, and the steel plate is rapidly cooled by the upper die and the lower die.

  According to the present invention, when manufacturing a press product having a difference in strength, it is possible to have a difference in strength within a single steel sheet without welding a plurality of blanks as in the tailored blank method. Compared with the tailored blank method, the number of components can be reduced.

  Moreover, since it is only necessary to press a steel plate having a uniform thickness at the time of press molding, the structure of the mold used for press working is not complicated.

  Furthermore, since welding work like the tailored blank method is not required, there is an advantage that the cost is low.

It is a front view which shows the schematic structure of the hardening apparatus of the steel plate in embodiment of this invention. It is a figure which shows the structure of the electromagnetic wave heater of the hardening apparatus of the steel plate in embodiment of this invention. It is a perspective view of a tailored blank.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a front view showing an outline of a steel plate quenching apparatus 100.

  The steel plate quenching apparatus 100 is provided with an electromagnetic wave heater 20 in the press molding apparatus 10, thereby enabling continuous quenching and press molding of the steel sheet 1.

  The press molding apparatus 10 includes a lower mold 12 attached on the lower base 11 and an upper mold 14 attached to the upper base 13. In this case, the upper die 14 is movable in the vertical direction, and the steel plate 1 is sandwiched between the upper die 14 and the lower die 12 by the downward movement of the upper die 14 so that press molding is performed. It is configured.

  The electromagnetic wave heater 20 includes a lower electromagnetic wave heater 21, an upper electromagnetic wave heater 22 disposed so as to face the lower electromagnetic wave heater 21, and a connecting member 24 that connects the lower electromagnetic wave heater 21 and the upper electromagnetic wave heater 22. Consists of. In this case, the electromagnetic wave heater 20 can be inserted between the lower mold 12 and the upper mold 14 of the press molding apparatus 10 by a horizontal movement device, and is configured to be movable out of the press molding apparatus 10.

  As shown in FIG. 1, the steel plate 1 is placed between the lower electromagnetic wave heater 21 and the upper electromagnetic wave heater 22 by the transport device with the electromagnetic wave heater 20 inserted between the lower mold 12 and the upper mold 14. Inserted. In this state, the steel sheet 1 is heated by being irradiated with electromagnetic waves generated from the lower electromagnetic wave heater 21 and the upper electromagnetic wave heater 22. This is because the energy of electromagnetic waves amplifies the movement of molecules constituting the steel plate 1.

  Thereafter, the electromagnetic wave heater 20 is taken out of the press molding apparatus 10 by a horizontal movement device. Then, by lowering the upper mold 14, the steel plate 1 is sandwiched between the upper mold 14 and the lower mold 12 and press molding is performed. At this time, the steel plate 1 comes into contact with the upper mold 14 and the lower mold 12 and is rapidly cooled.

  Next, the detailed structure of the electromagnetic wave heater 20 is demonstrated based on FIG. FIG. 2A is a top view of the electromagnetic wave heater 20 as viewed from the upper mold 14 side. FIG. 2B is a front view of the electromagnetic wave heater 20. In the figure, the state where the steel plate 1 is inserted between the upper electromagnetic wave heater 22 and the lower electromagnetic wave heater 21 is shown. In this case, the steel plate 1 is an automobile center pillar.

  The lower electromagnetic wave heater 21 includes three heater blocks 21a, 21b, and 21c that generate electromagnetic waves such as far infrared rays and an electromagnetic wave shielding plate 23A arranged in parallel in the horizontal direction. Similarly, the upper electromagnetic wave heater 22 includes three heater blocks 22a, 22b, and 22c that generate electromagnetic waves such as far infrared rays and an electromagnetic wave shielding plate 23B arranged in parallel in the horizontal direction. The reason why the pair of lower electromagnetic heater 21 and upper electromagnetic heater 22 is used is to heat the steel plate 1 more uniformly from both sides. When the steel plate 1 is relatively thin, only one of them is heated uniformly. can do.

  In this case, the three heater blocks 21a, 21b, 21c and the electromagnetic shielding plate 23A of the lower electromagnetic wave heater 21 and the three heater blocks 22a, 22b, 22c and the electromagnetic shielding plate 23B of the upper electromagnetic wave heater 22 are opposed to each other. Placed in. For example, the heater block 21 a of the lower electromagnetic wave heater 21 and the heater block 22 a of the upper electromagnetic wave heater 22 face each other.

  As shown in FIG. 2C, several plate-like heat generating plates 25 for generating electromagnetic waves are set in each of the heater blocks 21a to 21c and 22a to 22c. The number of heater blocks is not limited to three but can be increased or decreased by a necessary amount depending on the size of the irradiation area.

  In addition, a current control unit (not shown) is provided that allows a current to flow through each of the heater blocks 21a to 21c and 22a to 22c and can control the current value for each heater block. Thereby, the output of each heater block can be controlled. The output of the heater block is the product of the current flowing through the heater block and the applied voltage (current × voltage).

  In the present embodiment, for the lower electromagnetic wave heater 21, the two heater blocks 21a and 21b are set to high output, and the heater block 21c is set to low output. Therefore, for the lower electromagnetic wave heater 21, the electromagnetic wave shielding plate 23A is erected higher than the heater blocks 21b and 21c between adjacent heater blocks 21b and 21c having different outputs.

  This is to prevent the radiant heat of the electromagnetic waves generated from the heater blocks 21b and 21c from interfering with each other. Similarly, also for the upper electromagnetic wave heater 22, the two heater blocks 22a and 22b are set to high output and the heater block 22c is set to low output, so that electromagnetic waves are generated between adjacent heater blocks 22b and 22c having different outputs. The shielding plate 23B is erected higher than the heater blocks 22b and 22c. The electromagnetic shielding plates 23A and 23B are formed of a heat insulating material or the like that shields radiant heat of electromagnetic waves.

  Thereby, the heating temperature of the 1st area | region X of the steel plate 1 facing one heater block 21c of the lower electromagnetic wave heater 21 and one heater block 22c of the upper electromagnetic wave heater 22 is set with high accuracy by the heater block 21c. Can do. Further, the second region Y of the steel sheet 1 facing the two heater blocks 21a and 21b of the lower electromagnetic wave heater 21 and the two heater blocks 22a and 22b of the upper electromagnetic wave heater 22 (region different from the first region X). Can be set with high accuracy by the two heater blocks 21a and 21b.

  Next, a method for quenching the steel plate 1 will be described. As the steel plate 1, for example, a boron steel plate (a steel plate obtained by adding a small amount of boron and carbon to a steel material) is suitable for an automobile body. First, as shown in FIGS. 1 and 2, the steel sheet 1 is inserted between a lower electromagnetic wave heater 21 and an upper electromagnetic wave heater 22, and is radiated by electromagnetic waves generated from the lower electromagnetic wave heater 21 and the upper electromagnetic wave heater 22. Heated from both sides.

  In this case, as described above, the two heater blocks 21a and 21b of the lower electromagnetic wave heater 21 and the two heater blocks 22a and 22b of the upper electromagnetic wave heater 22 are set to high output, while the lower electromagnetic wave heater 21 The heater block 21c and the heater block 22c of the upper electromagnetic wave heater 22 are set to low output.

  As a result, the first region X of the steel plate 1 is irradiated with relatively weak electromagnetic waves from the heater block 21 c of the lower electromagnetic wave heater 21 and the heater block 22 c of the upper electromagnetic wave heater 22. The second region Y of the steel plate 1 is irradiated with relatively strong electromagnetic waves from the two heater blocks 21 a and 21 b of the lower electromagnetic wave heater 21 and the two heater blocks 22 a and 22 b of the upper electromagnetic wave heater 22.

  As a result, the second region Y of the steel plate 1 is heated to a temperature of 830 ° C. or higher, which is the transformation point of the steel plate 1, for example, 950 ° C. by strong electromagnetic wave radiant heat, and becomes an austenitic structure. The first region X of the steel plate 1 is heated to a temperature lower than 830 ° C., which is the transformation point of the steel plate 1, for example, 750 ° C. by radiant heat of a relatively weak electromagnetic wave.

  Next, the electromagnetic wave heater 20 is taken out of the press molding apparatus 10 and the upper mold 14 of the press molding apparatus 10 is moved downward so that the steel plate 1 is sandwiched between the upper mold 14 and the lower mold 12. Press molding is performed. Since the steel plate 1 at the time of press molding is softened by heating, it can be easily press-molded.

  In this case, as shown in FIG. 1, since the steel plate 1 is heated by the electromagnetic wave heater 20 in a state where the steel plate 1 and the electromagnetic wave heater 20 are inserted into the press molding apparatus 10, the electromagnetic wave heater 20 is taken out after the heating is completed. As a result, press molding can be performed quickly and without moving the heated steel plate 1. Thereby, the temperature fall accompanying the movement time of the steel plate 1 can be eliminated.

  The pressed steel sheet 1 is brought into contact with the upper mold 14 and the lower mold 12 and rapidly cooled. The cooling rate at this time needs to be a sufficient speed for the second region Y of the steel sheet 1 to change from the austenite structure state to the martensite structure state, and is, for example, 200 ° C./sec. Thereby, the 2nd field Y of steel plate 1 changes from the state of an austenite structure to the state of a martensite structure. As a result, the strength of the first region X of the steel plate 1 is the same as that before heating, but the strength of the second region Y of the steel plate 1 heated to the transformation point or more and rapidly cooled becomes considerably larger than that before heating.

  When the length × width size of the steel plate 1 is 1500 mm × 500-600 mm and the thickness is 1 mm to 2.3 mm, the strength of the first region X of the steel plate 1 after cooling is 590 MPa (megapascal), The intensity of the region Y was 1450 Mpa.

  Thus, according to this embodiment, unlike the tailored blank method, it is possible to have a difference in strength in one steel sheet 1 without welding a plurality of blanks, compared to the tailored blank method. Thus, the number of component parts can be reduced. Further, since the steel plate 1 having a uniform thickness may be press-molded during press working, the structures of the lower mold 12 and the upper mold 14 used for press molding are not complicated. Furthermore, since welding work like the tailored blank method is not required, there is an advantage that the cost is low.

  Further, by controlling the output of each heater block of the electromagnetic wave heater 20, the temperature management of each region of the steel plate 1 can be performed with high accuracy. In particular, by providing the electromagnetic wave shielding plates 23A and 23B in the electromagnetic wave heater 20 corresponding to the boundary portions of the regions having different temperature settings, the temperature setting can be performed with higher accuracy.

  In the present embodiment, the steel plate 1 is heated by the electromagnetic wave heater 20 in a state where the steel plate 1 and the electromagnetic wave heater 20 are inserted into the press molding device 10. However, the electromagnetic wave heater 20 is installed outside the press molding device 10. In addition, after heating the steel plate 1 with the electromagnetic wave heater 20, the heated steel plate 1 can be moved to the press molding apparatus 10 to perform press molding. In this case, as described above, a temperature drop occurs due to the movement of the steel sheet 1, and therefore it is necessary to set the heating temperature by the electromagnetic wave heater 20 high in consideration of the temperature drop.

  As the electromagnetic wave heater 20, one that generates far infrared rays as described above is suitable for heating the relatively large steel plate 1, but one that generates near infrared rays can also be used. Further, the size and thickness of the steel plate 1 can be freely selected, and the size of the electromagnetic wave heater 20 is determined according to the size of the steel plate 1.

DESCRIPTION OF SYMBOLS 1 Steel plate 10 Press molding apparatus 11 Lower base 12 Lower mold 13 Upper base 14 Upper mold 20 Electromagnetic heater 21 Lower electromagnetic heater 21a-21c Heater block 22 Upper electromagnetic heater 22a-22c Heater block 23A, 23B Electromagnetic shielding plate 24 Connecting member 25 Heating plate 100 Steel plate quenching device

Claims (5)

The surface of the first region of the steel plate is irradiated with an electromagnetic wave having a first strength, and the surface of the second region of the steel plate is irradiated with an electromagnetic wave having a second strength greater than the first strength. A first step of heating the second region to a temperature equal to or higher than the transformation point of the steel sheet;
A second step of changing the second region into a martensitic state by rapidly cooling the steel sheet after irradiation with electromagnetic waves, and setting the strength of the second region to the first region. A method of quenching a steel sheet, characterized by being higher than that of the steel sheet.   The steel sheet hardening method according to claim 1, wherein the electromagnetic wave is a far infrared ray.   The steel plate according to claim 1 or 2, wherein the second step is simultaneously performed by a press molding step using a metal mold, and the steel sheet is rapidly cooled by contacting the steel sheet with the metal mold. Hardening method. A press molding apparatus having an upper mold and a lower mold;
An electromagnetic wave heater having first and second heater blocks that can be freely inserted and removed between the upper mold and the lower mold, each of which can control output,
In a state where the electromagnetic wave heater is inserted between the upper mold and the lower mold, the electromagnetic wave heater irradiates the steel plate with electromagnetic waves, and then moves the electromagnetic wave heater to the outside of the press molding apparatus. A steel plate quenching apparatus, wherein the steel plate is press-molded between the upper die and the lower die, and the steel plate is rapidly cooled by the upper die and the lower die.   The steel plate hardening apparatus according to claim 4, wherein the electromagnetic wave heater includes an electromagnetic wave shielding wall disposed between the first heater block and the second heater block.

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