JP5311429B2 - Press curing method and apparatus comprising continuous processes - Google Patents

Description

  The present invention relates to a press curing method and apparatus therefor, and more particularly to a press curing method and apparatus comprising a continuous process in which hot rolling and press curing processes are integrated so as to simplify the process.

  Generally, steel sheets for general processing that are used in automotive parts generally have low formability when strength increases. Therefore, steel sheets with high strength but low strength are mainly used for parts that are complex and have a large amount of forming. Used for. As a result, the strength of the final part is low, and the material thickness is increased to ensure rigidity, so that the weight of the part increases. In order to solve this, a part for press hardening is applied.

  The method of manufacturing a press-hardened part is to heat a steel material improved in hardening ability by adding a boron (B) component at a high temperature of about 900 ° C., which is equal to or higher than the Ac3 transformation point, and then press this steel plate. This is a method of manufacturing high-strength automobile parts by rapidly forming into a product shape with a mold at once and martensite through rapid cooling.

  As is well known, steel sheets become more ductile when heated at high temperatures, making them superior in formability compared to cold-worked steel sheets, and their strength (over 1,400 MPa) contributes significantly to reducing the weight of automobiles. Moreover, since there is almost no deformation after processing (Springback), it is applied to ultra-high-strength parts that are difficult to form.

  In the press hardening process, as shown in FIG. 1, after the blank B before being hardened from the wound hot-rolled steel sheet coil C is reheated through the linear heating furnace O, the robot R moves to the press P side. It consists of a process of being transferred and press-molded (high temperature molding).

  Moreover, the hot-rolled steel sheet supplied to the conventional press-hardening process is made by reheating the molten metal from the electric furnace or blast furnace after making it into a slab by continuous casting, at a temperature above the austenite transformation temperature with good ductility (about 1100 ° C). After rolling, it is made into a desired size and form while removing the scale with high-pressure cooling water, and is manufactured into a coil form through a cooling process (slab casting).

  However, since the above-described method for manufacturing a press-curing part is separated from the hot-rolled steel sheet manufacturing process and the press-curing process, steps of reheating and cooling are added before the press-curing process, thereby reducing production costs. And there are disadvantages in terms of process time.

  That is, as shown in FIG. 2, the conventional method for manufacturing a press-curing part is as follows: (a) Molten metal production— (b) Continuous casting— (c) Slab production— (d) Slab reheating— (e) Heat Hot-rolled steel sheets manufactured by a slab casting process that proceeds in the order of cold rolling- (f) winding process, (g) blanking- (h) steel plate reheating- (i) forming- (j) cooling -(K) Since the press hardening process proceeds in the order of the finished product (high-strength part) manufacturing process, a steel plate reheating device should be accompanied without any problem.

  The present invention is for solving the above-mentioned conventional problems, and an object of the present invention is to perform a press curing step continuously with hot rolling in the manufacturing process of a press curing component. An object of the present invention is to provide a press curing method and apparatus comprising a continuous process integrating hot rolling and a press curing process line.

  According to the characteristics of the present invention for achieving the above-mentioned object, the present invention is a method for producing hot rolled steel by reheating and hot rolling a molten steel smelted in an electric furnace or a blast furnace after making it into a slab by continuous casting. A slab casting step for producing a steel plate; after the slab casting step, a blanking step for transferring the blanked steel plate to a blank through a closed oven and blanking; and after the blanking step, And a press curing step of transferring and press forming.

  A thin slab casting or strip casting process in which molten steel refined in an electric furnace or a blast furnace is produced into a hot-rolled steel sheet by continuous casting; and after the thin slab casting or strip-casting process is performed, A blanking step of transferring to a blank and blanking; and a press curing step of transferring the hot-rolled steel sheet to a press die disposed at an outlet of the hermetic oven after the blanking step and press-molding. .

  The blanking process of the hot-rolled steel sheet is a continuous process characterized in that it is performed in a closed oven that is supplied with hot air from a blast furnace or an electric furnace.

  The temperature inside the closed oven is maintained in the range of 1000 to 1200 ° C. so that the temperature of the hot-rolled steel sheet is maintained in the austenite region.

  The steel sheet press-formed in the press hardening step is cooled so that the structure becomes martensite.

  A path changing step of changing to a transfer path of the hot-rolled steel sheet when an abnormality occurs in the press die.

  In the path changing step, the detection unit detects an abnormality in the press mold, and the control unit receives a signal detected by the detection unit and determines whether an abnormality has occurred in the press mold. And a step of driving the emergency cutting machine and the guide roller when an abnormality occurs to change the transfer path of the hot-rolled steel sheet, and a step of winding the hot-rolled steel sheet having the changed transfer path.

  When an abnormality occurs in the press mold, a plurality of press dies are operated so that the blanked hot-rolled steel sheet can be continuously pressed, and the blanked hot-rolled steel sheet has an abnormality in the press mold. After the transfer direction is determined by the determination of the control unit that has received the signal of the detection unit that has detected the detection, the press die is pressed by a high-speed transfer device disposed between the exit side of the hermetic oven and the press die. Supplied to the mold.

  A slab casting facility for producing a hot-rolled steel sheet; a blank disposed on the exit side of the rolling mill of the slab casting facility and blanking the hot-rolled steel sheet to a certain size; an upper and lower mold on the exit side of the blank A press die for hot forming a hot-rolled steel sheet that is arranged vertically and blanked; provided between the outlet side of the rolling mill and the press die so that the blank is located inside, And a closed oven connected to an air passage of a blast furnace or an electric furnace so that the temperature of the hot-rolled steel sheet passing through the furnace is maintained in the austenite region.

  The closed oven includes an inlet and an outlet, and a transfer line extending from the inlet to the outlet is provided in the interior so as to transfer the hot-rolled steel sheet.

  Between the exit side of the rolling mill and the closed oven, a guide roller that guides the transfer path of the hot-rolled steel sheet to the exit lower side of the rolling mill when an abnormality occurs in the press die, and a lower portion by the guide roller And a winder that winds the hot-rolled steel sheet induced by the above.

  A plurality of the press dies are provided, and between the outlet side of the sealed oven and the press die, the hot rolled steel sheet discharged to the outlet side of the sealed oven is transferred to each press die. A high speed transfer device is provided.

  The present invention eliminates the cooling and winding process after hot rolling associated with the production of the steel sheet, and maintains the temperature during hot rolling at a high temperature so that the steel sheet is supplied to the press hardening process before the microstructure transformation. To do. In addition, after press molding, high-strength parts can be manufactured by controlling the cooling rate.

  In the above-described method, a high-temperature steel sheet that is produced during hot rolling is immediately put into the press hardening process, so that an additional reheating process is not necessary. Therefore, the cost reduction effect through process simplification can be expected.

  In addition, the present invention does not require a separate facility for cooling, winding, and reheating of the hot-rolled steel sheet, thereby reducing production costs and continuing the press hardening process following hot rolling. As a result, productivity is increased.

  In addition, the present invention has a configuration for the occurrence of an abnormality in the press mold, and has an effect of increasing production efficiency because the continuous process is continuously performed.

It is a block diagram which shows the conventional press hardening process roughly. It is process drawing which shows the conventional press hardening method. It is process drawing which shows the conventional press hardening method. It is process drawing which shows the press hardening method which consists of a continuous process which concerns on this invention. It is process drawing which shows the press hardening method which consists of a continuous process which concerns on this invention. It is the schematic which shows the structure of the sealing oven by which preferable embodiment of the press hardening apparatus which consists of a continuous process which concerns on this invention was employ | adopted. It is the schematic which shows the structure of the airtight oven by which other embodiment of the press hardening apparatus which consists of a continuous process which concerns on this invention was employ | adopted. It is the schematic which shows the structure of the sealing oven by which other embodiment of the press hardening apparatus which consists of a continuous process which concerns on this invention was employ | adopted. It is a CCT curve which shows the temperature change according to shaping | molding and cooling in the press hardening method which consists of a continuous process of this invention. It is process drawing which shows other embodiment of the press hardening method which consists of a continuous process which concerns on this invention. It is process drawing which shows other embodiment of the press hardening method which consists of a continuous process which concerns on this invention. It is a structure photograph of the press hardening type part manufactured by the present invention.

  Hereinafter, a press curing method and apparatus comprising a continuous process according to the present invention will be described in more detail with reference to the accompanying drawings.

  The press hardening method according to the present invention includes a slab casting process in which molten steel refined in an electric furnace or blast furnace is made into a slab by continuous casting, and then reheated and hot-rolled to produce a hot-rolled steel sheet; and the slab casting process The press-curing step of transferring, blanking, and press-molding the hot-rolled steel sheet manufactured in step 1 is continuously performed.

  For this purpose, the slab casting process and press hardening process are composed of continuous lines, and the hot-rolled steel sheet has a constant width instead of cooling and winding equipment on the exit side of the slab casting equipment that manufactures the hot-rolled steel sheet. A blank B to be cut and a press die P that is a high-temperature molding machine are arranged. For reference, the press mold P employs upper and lower molds, and has a series of configurations in which cooling water is provided in the upper and lower molds for hardening the surface structure of the hot-rolled steel sheet.

  With the configuration described above, the slab casting process proceeds in the order of (a) molten metal production, (b) continuous casting, (c) slab production, (d) slab reheating, (e) hot rolling process, and press hardening process. (F) Blanking-(g) Molding-(h) Cooling-(i) Finished product manufacturing process. The two steps are continuously performed, and the temperature changing during each step is as shown in FIGS.

  Through the above process, the hot-rolled steel sheet S finally hot-rolled by the slab casting equipment is transferred to the blank B, cut to a certain width, and continuously transferred to the press die P side and press-formed. Progress.

  The press forming is a high temperature forming, and the hot rolled steel sheet must be carried out at a temperature above the austenite transformation temperature with good ductility. To implement.

  The rolling and blanking process is a pre-stage of press forming, and if the hot-rolled steel sheet S is exposed to the atmosphere in the rolling and blanking process, cooling of about 20 ° C. occurs per second, and after the blanking process is completed. Since the austenite transformation temperature is low during press forming, the formability of the hot-rolled steel sheet is lowered. Therefore, it is necessary to provide a sealed section in the process before press molding. The sealed section also serves to prevent oxidation of the hot rolled steel sheet.

  As shown in FIG. 6, an internal space of a certain size is formed inside the sealed oven M, and the internal space communicates with the outside through an inlet and an outlet. Since the internal space is provided with a transfer line L extending in the inlet and outlet directions, the hot rolled steel sheet is configured to be transferred from the inlet to the outlet direction.

  The temperature of the closed oven M is maintained by blowing high temperature air from an electric furnace or blast furnace, and when the temperature during hot rolling is 1000 ° C. or higher, the hot rolled steel sheet blanked at the time of press forming, That is, 1000-1200 degreeC is maintained so that the temperature of hot-rolled steel plate blank S1 may be maintained at 900 degreeC or more. This takes into account the fact that the hot-rolled steel sheet travel time from the blanking process to the press-forming process is about 8 seconds, and the hot-rolled steel sheet is cooled during this time.

  However, since there may be a difference in the moving time and cooling of the hot-rolled steel sheet depending on the standard of the press forming equipment and the width and thickness of the hot-rolled steel sheet, the temperature inside the sealed oven M can be adjusted in consideration of this. it can. For this purpose, the closed oven M is connected to an air passage 10 of a blast furnace or an electric furnace so that high temperature air is constantly supplied to the internal space.

  On the other hand, since this invention consists of a continuous process, the structure prepared for the abnormality generation of a press die is prepared.

  As a first alternative, a winder 20 is provided at the lower part between the exit side of the rolling mill R and the closed oven M, as shown in FIG. The winder 20 is configured to wind the hot-rolled steel sheet without blanking when an abnormality occurs in the press die P.

  In the upper part of the winder 20, induction rollers 21 and 23 for guiding the hot-rolled steel sheet S to the winder 20 that is not the sealed oven M are provided.

  The guide rollers 21 and 23 include an upper guide roller 21 and a lower guide roller 23. The upper guide roller 21 is provided so as to be movable up and down with respect to the lower guide roller 23. When the press die is operated normally, the hot-rolled steel sheet S that is raised and hot-rolled is placed inside the sealed oven M. It is made to move naturally, and when the abnormality of the press die P occurs, it descends and guides the transfer path of the hot-rolled steel sheet S to the winder 20 that is not the sealed oven M.

  For reference, the upper guide roller 21 can be moved up and down by an external drive source or hydraulic pressure.

  A detection unit 25 for detecting the occurrence of an abnormality in the press die P is provided. The detector 25 is provided at a position close to the press die P and detects the occurrence of an abnormality in the press die P. The detection unit 25 is generally widely used as a general sensor. In addition, a signal from the detection unit 25 with respect to the occurrence of an abnormality in the press die P is transmitted to the control unit 27.

  When the control unit 27 receives the detection signal from the detection unit 25 and determines that an abnormality has occurred in the press die P, the control unit 27 lowers the upper guide roller 21 to the position of the lower guide roller 23, and the rolled heat Control is performed so that the rolled steel sheet S is guided to the lower part and wound by the winder 20.

  An emergency cutting machine 29 is provided between the exit side of the rolling mill R and the guide rollers 21 and 23. The emergency cutting machine 29 serves to cut the hot-rolled steel sheet S being transferred when the upper guide roller 21 is lowered. This is because in order to guide the rolled hot-rolled steel sheet S to the lower part and wind it by the winder 20, a cutting process of the hot-rolled steel sheet S being transferred is necessary.

  That is, the present invention includes a path changing step of changing to a transfer path of the hot-rolled steel sheet S when an abnormality occurs in the press die P.

  In the path changing process, the detection unit 25 detects an abnormality of the press die P and outputs a signal, and the control unit 27 receives an application of the signal detected by the detection unit 25 and an abnormality occurs in the press die P. The emergency cutting machine 29 and the guide rollers 21 and 23 are driven when an abnormality occurs, the step of changing the transfer path of the hot-rolled steel sheet S, and the winding of the hot-rolled steel sheet S with the changed transfer path are wound. And taking a step.

  For reference, a reference numeral 28 in FIG. 7 is a robot for transferring the hot-rolled steel sheet blank S1 to the press die P. In the present embodiment, the hot-rolled steel sheet blank S1 is illustrated as being supplied to the press mold P using a robot, but the present invention is not necessarily limited thereto, and the roller is pressed without using the robot. It can also be configured as a continuous line by connecting to the mold P.

  As a second alternative, as shown in FIG. 8, a plurality of press dies (P1, P2, P3) are operated. For example, if an abnormality occurs in one press mold P1, the hot-rolled steel sheet blank S1 drawn to the outlet of the closed oven M is distributed to the press molds (P2, P3) in which no abnormality has occurred. Thus, press molding is performed continuously.

  A high-speed transfer device 30 is provided between the closed oven M and the press dies P1, P2, and P3. The high-speed transfer device 30 is a device for transferring the hot-rolled steel sheet blank S1 drawn to the outlet of the closed oven M to any one of the plurality of press dies P1, P2, and P3.

  The high-speed transfer device 30 includes a main line 31 and an auxiliary line 33 branched from the main line 31. The main line 31 and the auxiliary line 33 are composed of, for example, a plurality of rollers. In the case of the main line 31, the roller rotates in the forward direction or the reverse direction to transfer the hot-rolled steel sheet blank S1 to each auxiliary line 33 side. To do.

  The hot-rolled steel sheet blank S1 transferred to the auxiliary line 33 side is transferred between the upper and lower molds and press-molded. At this time, a robot is provided at the end of the auxiliary line 33, and the transferred hot-rolled steel sheet blank S1 can be transferred between the press dies P1, P2, and P3 and between the lower dies.

  A detection unit 35 for detecting the occurrence of an abnormality in the press dies P1, P2, and P3 is provided. The detection unit 35 is provided at a position close to the press dies P1, P2, and P3, and detects the occurrence of an abnormality in the press dies P1, P2, and P3. The detection unit 35 is generally widely used as a general sensor. In addition, a signal from the detection unit 35 with respect to the occurrence of an abnormality in the press dies P1, P2, and P3 is transmitted to the control unit 39.

  The control unit 39 receives the application of the detection signal from the detection unit 35 and controls the operation of the high-speed transfer device 30 after determining the transfer direction of the hot-rolled steel sheet blank S1 drawn to the outlet of the sealed oven M.

  Specifically, when the control unit 39 receives the detection signal from the detection unit 35 and determines that an abnormality has occurred in the press die P1, heat is applied to the press dies P2, P3 in which no abnormality has occurred. The operation of the high-speed transfer device 30 is controlled so as to distribute the rolled steel sheet blank S1.

  When the second alternative is adopted, the press dies P1, P2, and P3 are variably operated according to the transfer speed of the hot-rolled steel sheet blank S1, and the temperature of the hot-rolled steel sheet blank S1 is maintained at a high temperature. Is advantageous.

  Moreover, even if an abnormality occurs in any one of the plurality of press dies P1, P2, P3, the hot-rolled steel sheet S finally hot-rolled by the slab casting equipment is transferred to the blank B. Then, it is cut into a constant width, and continuously transferred to the remaining press dies P2 and P3 and press-molded.

  The hot-rolled steel sheet that has been press-formed is water-cooled so as not to pass the ferrite and pearlite transformation curves having low strength in the CCT curve shown in FIG. 9 so that the structure of the hot-rolled steel sheet becomes martensite.

  On the other hand, the press hardening method mentioned above is applied not only to slab casting but also to thin slab casting and strip casting equipment with a short rolling line.

  When applied to thin slab casting and strip casting, as shown in FIG. 10 and FIG. 11, the manufacturing process of the press hardening component is as follows: (a) Molten metal production— (b) Continuous casting— (c) Hot rolled steel sheet -(D) Blanking-(e) Forming-(f) Proceeding in the order of cooling, the existing slab manufacturing and slab reheating, winding, and reheating processes for hot-rolled steel sheets for press forming are omitted. .

  Hereinafter, the operation of the press curing method comprising the continuous process according to the present invention will be described.

  A process of manufacturing a press-curing part will be described with reference to FIGS.

  First, if the continuously cast slab is hot-rolled, the rolled hot-rolled steel sheet S is transferred into the closed oven M. The hot-rolled steel sheet charged in the closed oven is transferred to the blank B side via a transfer line and blanked (cut) to a certain size. The blanked hot-rolled steel sheet S1 is continuously transferred and then pulled out to the outlet side of the closed oven M.

  At this time, the internal temperature of the closed oven M is about 1000 ° C., and serves to maintain the temperature of the hot-rolled steel sheet in the austenite region until press forming. The section in which the closed oven M is provided can have a difference in position in consideration of the temperature in the hot rolling process of slab casting and thin slab casting / strip casting (see FIGS. 10 and 11).

  Subsequently, the hot-rolled steel sheet blank S1 drawn to the outlet of the closed oven M is transferred between the upper mold and the lower mold and manufactured as a finished product S2 by press molding. The hot-rolled steel sheet that has been press-formed is made into martensite having a high structure strength by water cooling.

  As a result of the experiment, it was confirmed that the press-curing part manufactured by the above-described process has the martensite structure shown in FIG.

  The press curing method consisting of such continuous processes is composed of a continuous line of blanks and press dies for the press curing process on the exit side of the slab casting equipment and the thin slab casting equipment / strip casting equipment. The manufacturing process for parts is made in a continuous line to simplify the process.

  This eliminates the step of cooling after hot rolling and winding with a coil and the step of reheating the hot-rolled steel sheet for press forming. Here, even if the reheating step is omitted, high-strength parts can be manufactured because the temperature until the hot-rolled steel sheet after hot rolling is press-formed is maintained above the austenite transformation temperature by a closed oven.

  On the other hand, when an abnormality occurs in the press die P, the upper guide roller 21 is lowered to the position of the lower guide roller 23, the rolled hot-rolled steel sheet S is guided to the lower part, and is wound by the winder 20. In preparation for abnormalities in the press mold.

  Also, a plurality of press dies P1, P2, and P3 are provided, and even if any one of the dies P1 is abnormal, the process of being transferred to the remaining press dies P2 and P3 and being press-molded is continuous. Proceed to.

  It is clear that other various modifications are possible within the scope of the basic technical idea of the present invention as long as the person has ordinary knowledge in the art. Should be construed based on the claims that follow.

Claims (12)

A slab casting process in which molten steel is made into a slab by continuous casting and then reheated and hot rolled to produce a hot rolled steel sheet;
After implementation of the slab casting step, through the inlet of the dense closed oven, a blanking step of blanking by transferring the hot-rolled steel sheet to blanking section for cutting;
After the blanking step , a press curing step of transferring to a press mold and press forming;
Only including,
The temperature of the hot-rolled steel sheet is maintained in the austenite region between the hot rolling and the press hardening process, and is a press hardening method comprising a continuous process. A thin slab casting or strip casting process for producing molten steel into a hot rolled steel sheet by continuous casting;
Wherein after the implementation of the thin slab casting or strip casting process, through the inlet of the sealed oven and blanking process of blanking by transferring the hot-rolled steel sheet to blanking section for cutting;
After the blanking step , a press hardening step of transferring the hot-rolled steel sheet to a press die disposed at the outlet of the sealed oven and press-molding;
Only including,
The temperature of the hot-rolled steel sheet is maintained in the austenite region between the hot rolling and the press hardening process, and is a press hardening method comprising a continuous process. The closed oven is supplied with hot air from a blast furnace or an electric furnace,
The press hardening method comprising a continuous process according to claim 1 or 2, wherein the blanking process of the hot-rolled steel sheet is performed in the sealed oven.   The press hardening method comprising a continuous process according to claim 3, wherein the temperature inside the sealed oven is maintained in a range of 1000 to 1200 ° C so that the temperature of the hot-rolled steel sheet is maintained in the austenite region. .   The press hardening method comprising a continuous process according to claim 4, wherein the steel sheet press-formed in the press hardening process is cooled so that the structure becomes martensite.   The press hardening method comprising a continuous process according to any one of claims 1 to 5, further comprising a path changing step of changing to a transfer path of the hot-rolled steel sheet when an abnormality occurs in the press mold. . The route changing step includes
A step in which the detection unit detects an abnormality of the press die and outputs a signal;
The control unit receives an application of the signal detected by the detection unit, determines whether or not an abnormality has occurred in the press mold, and drives the emergency cutting machine and the induction roller when the abnormality occurs to transfer the hot-rolled steel sheet. Step to change the
And a step of winding the hot-rolled steel sheet whose transfer path is changed. The press hardening method comprising a continuous process according to claim 6. When an abnormality occurs in the press die, a plurality of press dies are operated so that the blanked hot-rolled steel sheet can be continuously press-formed,
The blanked hot-rolled steel sheet, after the transport direction by the determination of the control unit which receives the application of the press die abnormality sensed detection of the signal has been determined, the the exit side of the sealed oven The press curing method comprising a continuous process according to any one of claims 1 to 7, wherein the press mold is supplied to a corresponding press mold by a high-speed transfer device disposed between the press molds. Slab casting equipment for producing hot-rolled steel sheets;
Wherein disposed on the outlet port side of the rolling mill slab casting facilities, and the blanking portion of the hot-rolled steel sheet to blanking;
On the exit side of the blanking section, the lower mold are arranged vertically, and a press die for hot forming hot-rolled steel sheet is blanked;
Blast furnace so that the blanking portion is provided between the rolling mill exit side to the press die so as to be positioned inside, the temperature of the hot-rolled steel sheet that passes through the inside is maintained in the austenitic region Or a closed oven connected to the air passage of the electric furnace;
A press curing apparatus comprising a continuous process characterized by comprising: The continuous oven according to claim 9 , wherein the closed oven includes an inlet and an outlet, and a transfer line extending from the inlet to the outlet is provided to transfer the hot-rolled steel sheet. A press curing device consisting of processes. Between the rolling mill exit side to the sealed oven has a guide roller for guiding the transfer path of the hot-rolled steel sheet exit side lower portion of the rolling mill upon occurrence of abnormality in the press die,
The press hardening apparatus comprising a continuous process according to claim 10 , further comprising a winder that winds the hot-rolled steel sheet guided to the lower part by the guide roller. A plurality of the press dies are provided,
Wherein during exit side of the sealed oven and the press die, the high-speed transfer device is provided for transferring the hot-rolled steel sheet discharged to the exit side of the sealed oven to each of the press die The press hardening apparatus which consists of a continuous process of Claim 10 or 11 characterized by these.

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