JP2010172948A - Method and apparatus for performing hot press-forming of steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the generation of oxidized scale on the surface of a steel sheet in hot press-forming in which the steel sheet is cooled with water when press-forming the steel sheet at high temperature. <P>SOLUTION: When performing the hot press-forming of the steel sheet 2 which is heated to the high temperature by using a die 3 on the surface of which a plurality of projecting parts are formed, the water 4 is supplied as a coolant to clearances between the steel sheet 2 and the die 3, which are formed with the plurality of the projecting parts. At this time, the quantity of dissolved oxygen in the water 4 which is supplied as the coolant is adjusted at ≤1 ppm. Then, when using a steel sheet 2 on which plating treatment is not applied, the oxidized scale which is generated on the steel sheet 2 is suppressed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a forming method and a forming apparatus for suppressing generation of oxide scale on the surface of a steel plate in hot press forming in which a coolant is supplied to the steel plate and cooled when the hot steel plate is press-formed.

  In recent years, hot press forming, which has been increasingly used as a steel plate forming means for automobile parts using high-tensile steel plates, has a lower deformation resistance by forming at a higher temperature than cold press forming. It is press-molded into a desired shape without causing molding defects such as cracks, wrinkles, and deformation after molding.

  In the hot press forming method, a punch is lowered to the bottom dead center in a state where a steel plate heated to a predetermined temperature in a heating furnace is placed on a die, and then the steel plate is cooled for a certain time. When the formed steel plate after cooling is removed from the die, a new steel plate heated to a predetermined temperature is placed on the die. Therefore, in hot press forming, it is important to shorten the cooling time after forming a steel sheet from the viewpoint of productivity.

  As a means for shortening the cooling time of the steel sheet after forming, for example, a coolant supply mechanism that supplies water as a coolant to the steel sheet is provided inside the mold, and a plurality of independent heights are provided on the surface of the mold. Patent Document 1 discloses a method of providing a raised protrusion and supplying a coolant to a steel plate after hot press forming. According to Patent Document 1, since the refrigerant and the vapor of the refrigerant flow through a gap formed by the convex portion on the mold surface and the steel plate, the metal plate material is cooled in a short time, and the hot press forming productivity is increased. be able to.

JP 2005-169394 A

  By the way, in the above-mentioned hot press forming, when a steel plate is heated in a heating furnace for forming, an oxidized scale is generated on the surface of the steel plate, which adversely affects subsequent processes after forming, for example, a coating process. I know to give. This oxidized scale can be removed by applying, for example, sand blasting to the steel sheet after forming, but since sand blasting equipment and work space are separately required, the oxide scale should not be generated in the heating furnace as much as possible. It is preferable. Therefore, normally, in order to suppress the occurrence of oxide scale on the surface of the steel sheet in the heating furnace, the steel sheet is heated in a non-oxidizing atmosphere in the heating furnace, or a steel sheet with an aluminum plating on the surface is used, etc. Measures are taken.

  However, according to the inventors, while the hot press molding is repeatedly performed by the hot press molding method disclosed in Patent Document 1, the above-described measures for suppressing the generation of oxide scale are taken. It was confirmed that oxide scale was deposited in the recesses between the protrusions on the mold surface. And the accumulation of the oxide scale in the concave portion closes the gap formed by the convex portion of the mold and the steel plate during hot press molding, thereby locally inhibiting the cooling of the steel plate, and the product after molding The problem that the quality of the deteriorated.

  As a result of investigations by the inventors, when this non-plated plain steel is used as a forming steel plate, the surface of the steel material is caused by oxygen contained in water used as a refrigerant, that is, dissolved oxygen. It was found that it was generated by oxidation. And the clogging of the gap formed by the convex part of the mold and the steel plate is due to the scale that the oxide scale generated on the surface of the steel material adheres to the convex part of the mold during hot press molding and adheres to the convex part. It has been confirmed that this is caused by peeling off and depositing in the concave portion between the convex portions. For this reason, when ordinary steel is used as the steel plate, it is necessary to frequently clean the mold as a measure against clogging of the concave portion, and the problem is that the productivity of the hot press forming apparatus decreases due to the stoppage of the apparatus due to the cleaning work. It was happening.

  This invention is made | formed in view of this point, and it aims at suppressing generation | occurrence | production of the oxide scale in the steel plate surface in the hot press forming which cools a steel plate with water at the time of press forming of a high temperature steel plate.

  In order to achieve the above object, the present invention, when hot press molding using a mold having a convex portion formed on the surface, water is supplied to the gap between the steel plate and the mold formed by the convex portion. In the hot press forming method of supplying and cooling the steel sheet, the water has a dissolved oxygen content adjusted to 1 ppm or less.

  As will be described later, when the inventors investigated, the water whose adjusted oxygen amount was adjusted to 1 ppm or less was used for cooling the steel sheet, thereby suppressing the oxide scale generated on the surface of the steel sheet during hot press forming. I knew it was possible. Therefore, it is possible to prevent the oxide scale from being blocked in the gap between the steel plate and the mold, which is formed by the convex portions of the mold, and hindering uniform cooling of the steel plate. In addition, this eliminates the need for frequent cleaning work, so that it is possible to prevent the productivity of the hot press forming apparatus from being lowered.

  The water in which the amount of dissolved oxygen is adjusted may be generated by blowing a non-oxidizing gas into the water stored in the container, or may be generated by reducing the pressure in the container storing the water. Moreover, you may produce | generate by heating the water stored in the container.

  According to another aspect of the present invention, when hot press molding is performed using a mold having a convex portion formed on the surface, water is supplied to the gap between the steel plate and the mold formed by the convex portion, and A hot press forming apparatus for cooling a steel plate, a container for storing water to be supplied to the mold, a gas supply pipe for supplying non-oxidizing gas into water stored in the container, It is characterized by having.

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of the oxide scale of a steel plate can be suppressed in the hot press forming which cools a steel plate rapidly when press-forming a high temperature steel plate.

It is a longitudinal cross-sectional view which shows the outline of a structure of the hot press molding apparatus concerning this Embodiment. It is an enlarged view of a die surface of a hot press molding die. It is an enlarged view of the cross section of the die | dye of a hot press molding die. It is a longitudinal cross-sectional view which shows other embodiment of the hot press molding apparatus by this invention. It is a longitudinal cross-sectional view which shows other embodiment of the hot press molding apparatus by this invention.

  Hereinafter, embodiments of the present invention will be described. FIG. 1 is a longitudinal sectional view showing an outline of a configuration of a hot press forming apparatus 1 according to an embodiment.

  A hot press forming apparatus 1 is connected to a mold 3 for forming a steel plate 2, a container 5 for storing water 4 supplied as a coolant to the mold 3, and a container 5 and the mold 3. The water supply pipe 6 for supplying the water 4 to the mold 3 is provided. A mold 3 for forming the steel plate 2 is composed of a die 10 that is a lower mold and a punch 11 that is an upper mold. In the present embodiment, the steel plate 2 is plain steel whose surface is not plated.

  The forming surface 10a of the die 10 is provided with a refrigerant supply port 12 for supplying water 4 to the steel plate 2 when the punch 11 is lowered to the bottom dead center and the steel plate 2 is hot press formed. The coolant supply port 12 communicates with a flow path 13 of water 4 provided inside the die 10, and the flow path 13 is connected to the water supply pipe 6. Moreover, as shown in FIG.2 and FIG.3, the some convex part 14 of the fixed height is formed in the shaping | molding surface 10a. As a result, when the punch 11 is lowered to the bottom dead center, the coolant is inserted into the recesses between the plurality of projections 14 and the projections 14, that is, the gap formed between the die 10 and the steel plate 2 by the projections 14. The water 4 supplied from the supply port 12 is allowed to flow, and the steel plate 2 can be cooled in a short time.

  The container 5 is an airtight pressure vessel, and includes a gas supply pipe 20 that introduces a non-oxidizing gas 15 supplied from a gas supply source (not shown) at a predetermined pressure into the container 5, and the container 5. A discharge pipe 21 that discharges the atmosphere in the container 5 to the outside, and a supply pipe 22 for supplying water 4 to the container 5. The gas supply pipe 20 is connected to a position where the non-oxidizing gas 15 can be blown into the water 4 stored in the container 5, for example, the bottom surface of the container 5. The release pipe 21 is provided with a relief valve 23, and the pressure inside the container 5 is supplied from the gas supply pipe 20 by adjusting the discharge amount of the atmosphere in the container 5 by the relief valve 23. The pressure is kept lower than the pressure. Thereby, the pressure in the container 5 and the pressure of the non-oxidizing gas 15 supplied to the gas supply pipe 20 are equalized, and the non-oxidizing gas 15 is prevented from being supplied into the container 5. The relief valve 23 only needs to maintain the pressure in the discharge pipe 23 provided in communication with the upper surface of the container 5 below the pressure of the non-oxidizing gas 15 supplied from the gas supply pipe 20. . Therefore, for example, a primary side, that is, a mechanical pressure control valve that controls the pressure inside the container 5 may be used, and the measurement result of a pressure measuring mechanism (not shown) that measures the pressure inside the container 5 may be used. A remotely operable valve that controls the pressure in the container 5 by adjusting the opening of the relief valve 23 via a control device (not shown) may be used.

  A shutoff valve 24 is provided in the vicinity of the die 10 of the water supply pipe 6. The shutoff valve 24 is opened and closed by a signal from a control device (not shown), for example. The opening / closing operation may be performed automatically in accordance with, for example, the state of hot press forming, that is, the top and bottom of the punch 11, or the operator may be configured to perform remote operation from the control device. As the shut-off valve, an electromagnetic valve, an air operated valve, an electric valve or the like can be used.

  The supply pipe 22 is connected to a water pump (not shown), and the water 4 is fed to the container 5 at a pressure higher than the pressure in the container 5 by the water pump. The supply of water 4 from the supply pipe 22 is continuously performed so that the water level of the water 4 in the container 5 is always constant based on, for example, a measurement result of a water level meter (not shown) that measures the water level in the container 5. Replenishment may be performed, or replenishment may be performed intermittently so that replenishment is performed when the preset lower limit water level is reached, and replenishment is stopped when the upper limit water level is reached.

  The hot press forming apparatus 1 according to the present embodiment is configured as described above. Next, hot press forming of the steel sheet 2 by the hot press forming apparatus 1 will be described.

  First, water 4 is supplied in advance to a predetermined water level in the container 5, and the non-oxidizing gas 15 is continuously supplied into the container 5 through the gas supply pipe 20 with the shut-off valve 14 closed. At this time, since the gas supply pipe is connected to the bottom surface of the container 5, the water 4 in the container 5 is bubbled by the non-oxidizing gas 15, and oxygen dissolved in the water 4, that is, dissolved oxygen is reduced. For this reason, the container 5 functions as a so-called deaeration device that removes dissolved oxygen in the water 4 and can adjust the amount of dissolved oxygen in the water 4 to a predetermined value. At this time, the amount of dissolved oxygen is preferably 1 ppm or less. The condition that the dissolved oxygen amount is 1 ppm or less is based on the results of Examples described later. The non-oxidizing gas 15 may be any gas that can reduce the amount of dissolved oxygen in the water 4 by bubbling. Nitrogen gas, helium gas, argon gas, or the like can be used. In the form, nitrogen gas is used.

  And the amount of dissolved oxygen in the water 4 in the container 5 becomes 1 ppm or less, the inside of the container 5 is pressurized by the non-oxidizing gas 15 supplied from the gas supply pipe 20, and the atmosphere in the container 5 by the relief valve, That is, after the release of oxygen removed from the water 4 from the non-oxidizing gas 15 and bubbling is started and the pressure in the container 5 is maintained at a predetermined value, the steel plate 2 heated in advance in a heating furnace (not shown) is used. Place on the die 10. Thereafter, the punch 11 is lowered to the bottom dead center, and hot press forming of the steel plate 2 is performed. Next, the shutoff valve 14 of the water supply pipe 6 is opened with the punch 11 held at the bottom dead center position. Thereby, the water 4 is supplied to the steel plate 2 through the water supply pipe 6 and the coolant supply port 12 by the pressure of the non-oxidizing gas 15 accumulated in the container 5, and the formed steel plate 2 is cooled. Then, when the cooling of the steel plate 2 is completed and the formed steel plate 2 is removed from the die 10, the heated new steel plate 2 is placed on the die 10 and a series of hot press forming steps are repeated.

  According to the above embodiment, the amount of dissolved oxygen in the water 4 used as the refrigerant of the steel plate 2 can be reduced by bubbling the water 4 in the container 5 with the non-oxidizing gas 15. For this reason, even when plain steel is used as the steel plate 2, it is possible to suppress oxide scale generated on the surface of the steel plate 2 during hot press forming. Therefore, it is possible to prevent the uniform cooling of the steel plate 2 from being hindered due to the gap between the steel plate 2 and the mold 3 formed by the plurality of convex portions 14 being blocked. And since it is not necessary to frequently perform the cleaning work of the mold to prevent the blockage, it is possible to prevent the productivity of the hot press molding apparatus 1 from being lowered.

  Moreover, since it can suppress that the metal mold | die 3 rusts or corrodes by using the water 4 with little dissolved oxygen amount for a refrigerant | coolant, it also contributes to the lifetime extension of the metal mold | die 3 itself. Furthermore, since it can also suppress that an oxide scale generate | occur | produces in the refrigerant | coolant supply port 12 in the metal mold | die 3, it can prevent that the inside of the refrigerant | coolant supply port 12 obstruct | occludes.

  In the above embodiment, the convex portion 14 and the refrigerant supply port 12 are provided in the die 10. However, the convex portion 14 and the refrigerant supply port 12 may be provided in the punch 11, and in any case. The steel plate 2 can be cooled.

  In the above embodiment, the non-oxidizing gas 15 is continuously supplied. However, once the dissolved oxygen is reduced to a desired value by bubbling, the amount of dissolved oxygen in the water 4 is as long as the water 4 is not newly replenished. Since it increases, it is not always necessary to perform bubbling. Therefore, when the water 4 is not replenished in the container 5, the supply of the non-oxidizing gas 15 is stopped and the water 4 is replenished or when the pressure in the container 5 becomes a predetermined value or less. You may make it start supply again.

  In the above embodiment, the water 4 in the container 5 is supplied to the refrigerant supply port 12 by pressurizing the inside of the container 5 with the non-oxidizing gas 15, but the non-oxidizing gas 15 gas supplied into the container 5 is used. For example, the water 4 may be supplied from the container 5 to the refrigerant supply port 12 by providing a pump or the like in the water supply pipe 6.

  In the above embodiment, bubbling by the non-oxidizing gas 15 is used as a means for removing dissolved oxygen. However, the present invention is not limited to this embodiment as long as the dissolved oxygen in the water 4 can be removed. For example, a method of reducing the pressure in the container 5 or heating the water 4 in the container 5 can be proposed.

  When the inside of the container 5 is decompressed to remove dissolved oxygen, for example, as shown in FIG. 4, the inside of the container 5 is decompressed by a vacuum pump 31 as a decompression device via a suction tube 30, and the refrigerant is removed from the container 5. The hot press molding apparatus 1 may be configured so that the water 4 is supplied to the supply port 12 by, for example, another pump 32. In this case, the relief valve 23 is used as a vacuum breaking valve for sucking the atmosphere when the inside of the container 5 is over-vacuum.

  When the water 4 in the container 5 is heated to remove dissolved oxygen, for example, an electric heater is provided in the water 4 as a heating means for the water 4, or, for example, as shown in FIG. A method of heating the water 4 to the boiling point or close to the boiling point by supplying superheated steam as the heating medium 41 through the heat source supply pipe 40 into the boiling point 4 is conceivable. Also in this case, since pressurization in the container 5 by the non-oxidizing gas 15 is not performed, it is conceivable to supply the water 4 from the container 5 to the refrigerant supply port 12 using the pump 32. When the water 4 heated to near the boiling point is used as a refrigerant for the steel plate 2, the water 4 remaining on the surface of the steel plate 2 after the steel plate 2 is cooled evaporates faster than when cooled with the water 4 at room temperature. . For this reason, the time which dries the steel plate 2 for post-processing becomes short, and productivity of hot press molding improves. In this case, a vent pipe 42 may be provided in place of the relief valve 23, and the container 5 may be kept open to the atmosphere at all times.

  In addition, as a method of generating water 4 from which dissolved oxygen is removed, a method of cooling and condensing water vapor can be proposed.

  Hereinafter, as an example, hot press molding is performed using the hot press molding apparatus 1, and the relationship between the amount of dissolved oxygen in water 4 used as a refrigerant and the clogging of the gap between the convex portion 14 and the steel plate 2 is confirmed. A test was conducted. As the mold 3 of the hot press molding apparatus 1, a die having a convex surface 14 having a diameter of 1 mm, a height of 0.5 mm, and a pitch of 1.5 mm on the molding surface 10 a of the die 10 was used. The steel plate 2 was plain steel having a length of 300 mm, a width of 100 mm, and a thickness of 1.2 mm. The material of the die 10 and the punch 11 was S45C, the shoulder width was 5 mm, the die width was 70 mm, and the die forming depth was 60 mm. Nitrogen gas and helium gas are used as the non-oxidizing gas 15 for bubbling the water 4 in the container 5, and the amount of dissolved oxygen is reduced to 1 ppm (Example 1) and 0 by bubbling the water 4 with the nitrogen gas for a predetermined time. The amount of dissolved oxygen was adjusted to 0.01 ppm (Example 3) by bubbling to 0.1 ppm (Example 2) with helium gas for a predetermined time. At this time, the supply pressures of nitrogen gas and helium gas into the container 5 were both 0.95 MPa, and the pressure in the container 5 was controlled to 0.9 MPa by the relief valve 23. The relationship between the time for bubbling the water 4 with the non-oxidizing gas 15 and the amount of decrease in dissolved oxygen is obtained in advance by other experiments.

  And the steel plate 2 was heated to 950 degreeC in the atmosphere of the non-oxidizing gas 15 in the heating furnace, the heated steel plate 2 was mounted on the die | dye 10, and hot press molding was performed. In the hot press forming, the steel plate 2 was cooled by holding the die 10 at the bottom dead center for 2 seconds and ejecting water 4 adjusted in the amount of dissolved oxygen from the refrigerant supply port 12. Thereafter, the formed steel plate 2 was removed from the mold 3. And this hot press molding was performed 1000 times continuously. The number of 1000 times is the minimum required to perform hot press molding continuously without clogging the gap between the convex portion 14 and the mold 3 with the oxide scale from the viewpoint of productivity. Is the number of times.

  Further, in this embodiment, as compared with the prior art, the same hot press molding is performed using water 4 that is not bubbled by a non-oxidizing gas, that is, the amount of dissolved oxygen is not adjusted, as a refrigerant. Was performed 1000 times continuously. The water 4 in which the dissolved oxygen amount is not adjusted is pressurized in the container 5 through another gas supply pipe 27 provided at a position where the water 4 is not bubbled, for example, as shown by a broken line in FIG. Then, it is supplied to the mold 3. Note that nitrogen gas and compressed air were used as the pressurizing gas supplied from the gas supply pipe 27. The supply pressure was 0.9 MPa as in the case of bubbling. At this time, the amount of dissolved oxygen in the water 4 when pressurized with air and the water 4 when pressurized with nitrogen gas was confirmed to be 10 ppm (conventional 1) and 4 ppm (conventional 2), respectively.

  Table 1 shows the results of inspecting the mold 3 after performing hot press molding continuously 1000 times using the water 4 having the five dissolved oxygen amounts as a refrigerant. If the gap between the convex portion 14 of the die 10 and the steel plate 2 is not closed by the oxide scale, it is determined as good and is shown in Table 1 as ◯.

  As a result, as shown in Table 1, if the dissolved oxygen content of the water 4 is 1 ppm or less, the gap between the convex portion 14 and the steel plate 2 due to the oxide scale even after hot press forming is performed 1000 times continuously. It was found that no obstruction occurred.

  The present invention is useful when continuously hot pressing a steel sheet.

DESCRIPTION OF SYMBOLS 1 Hot press molding apparatus 2 Steel plate 3 Mold 4 Water 5 Container 6 Water supply pipe 10 Die 10a Molding surface 11 Punch 12 Refrigerant supply port 13 Flow path 14 Convex part 15 Non-oxidizing gas 20 Gas supply pipe 21 Release pipe 22 Replenishment Pipe 23 Relief valve 24 Shut-off valve 27 Gas supply pipe 30 Suction pipe 31 Vacuum pump 32 Pump 40 Heat source supply pipe 41 Heating medium 42 Vent pipe

Claims (5)

Hot press for cooling the steel sheet by supplying water to the gap between the steel sheet and the mold formed by the convex part when hot pressing using a mold having a convex part on the surface In the molding method,
The hot press molding method, wherein the water has a dissolved oxygen content adjusted to 1 ppm or less. The hot press molding method according to claim 1, wherein the water whose adjusted oxygen amount is adjusted is generated by blowing a non-oxidizing gas into the water stored in the container. The hot press molding method according to claim 1, wherein the water in which the amount of dissolved oxygen is adjusted is generated by decompressing a container in which water is stored. The hot press molding method according to claim 1, wherein the water in which the dissolved oxygen amount is adjusted is generated by heating water stored in a container. Hot press for cooling the steel sheet by supplying water to the gap between the steel sheet and the mold formed by the convex part when hot pressing using a mold having a convex part on the surface A molding device,
A container for storing water to be supplied to the mold;
A hot press molding apparatus comprising: a gas supply pipe for supplying a non-oxidizing gas into water stored in the container.

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