KR20140075954A - Hot forming steel pipe having multi-microstructure due to different cooling and method of manufacturing the same - Google Patents

Hot forming steel pipe having multi-microstructure due to different cooling and method of manufacturing the same Download PDF

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Publication number
KR20140075954A
KR20140075954A KR1020120143744A KR20120143744A KR20140075954A KR 20140075954 A KR20140075954 A KR 20140075954A KR 1020120143744 A KR1020120143744 A KR 1020120143744A KR 20120143744 A KR20120143744 A KR 20120143744A KR 20140075954 A KR20140075954 A KR 20140075954A
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South Korea
Prior art keywords
steel pipe
mold
hot
cooling
steel
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KR1020120143744A
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Korean (ko)
Inventor
박성필
백승철
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현대하이스코 주식회사
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Priority to KR1020120143744A priority Critical patent/KR20140075954A/en
Publication of KR20140075954A publication Critical patent/KR20140075954A/en

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0062—Heat-treating apparatus with a cooling or quenching zone
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Heat Treatment Of Articles (AREA)

Abstract

The present invention provides a method of manufacturing a hot-formed steel pipe that simultaneously realizes rigidity and shock absorption. A method of manufacturing a hot-formed steel pipe according to an embodiment of the present invention includes heating a steel pipe containing carbon in a range of 0.22 wt% to 0.28 wt%; Inserting the steel pipe into a mold having a slow cooling region and a quenching region and through which a cooling fluid is injected in the quenching region; And compressing the metal mold to the steel pipe and performing differential cooling of the steel pipe by the cooling fluid to hot-mold the steel pipe.

Description

TECHNICAL FIELD The present invention relates to a hot-formed steel pipe having multiple structures due to differential cooling and a method of manufacturing the same.

TECHNICAL FIELD OF THE INVENTION The present invention relates to a steel material, and more particularly, to a hot-formed steel pipe having multiple structures by differential cooling and a manufacturing method thereof.

Hot forming is a method of forming a steel tube by heating it to a high temperature and then molding it by using a mold, and at the same time cooling the metal mold by a cooling effect so that the temperature of the steel tube is drastically lowered. .

However, since the steel pipe manufactured by such hot forming maintains high strength as a whole, deformation due to vehicle collision is suppressed when applied to a vehicle, so that it is difficult to absorb impact energy. Therefore, when a vehicle collision occurs, the passenger has a limitation of suffering a serious injury by an external impact caused by a collision. Therefore, there is a demand for a steel pipe capable of achieving both of the two purposes of securing rigidity and shock absorption.

1. Korean Patent Publication No. 10-2012-0016777 2. Korean Patent Publication No. 10-2011-0062428

The technical problem to be solved by the technical idea of the present invention is to provide a method of manufacturing a hot-formed steel pipe that simultaneously realizes rigidity and impact absorption.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a hot-formed steel pipe which realizes rigidity and impact absorption at the same time.

However, these problems are illustrative, and the technical idea of the present invention is not limited thereto.

According to an aspect of the present invention, there is provided a method of manufacturing a hot-formed steel pipe, comprising: heating a steel pipe containing carbon in a range of 0.22 wt% to 0.28 wt%; Inserting the steel pipe into a mold having a slow cooling region and a quenching region and through which a cooling fluid is injected in the quenching region; And compressing the metal mold to the steel pipe and performing differential cooling of the steel pipe by the cooling fluid to hot-mold the steel pipe.

In some embodiments of the present invention, the step of hot-forming the steel pipe may include directing the cooling fluid supplied through the cooling channel formed in the metal mold to a part of the steel pipe from the mold, Can be quenched to generate martensitic transformation.

In some embodiments of the present invention, the step of hot-forming the steel pipe comprises contacting a part of the metal held at a temperature causing martensitic transformation to a part of the steel pipe, Can be generated.

In some embodiments of the present invention, the step of hot-forming the steel pipe may be such that a part of the steel pipe is in contact with the slow cooling area of the metal mold to prevent martensitic transformation. Another part of the steel pipe may come into contact with the quenched area of the mold to cause martensitic transformation.

In some embodiments of the present invention, the cooling fluid may comprise water in the range of 0 ° C to 100 ° C.

In some embodiments of the present invention, the heating may heat the steel tube to a temperature in the range of 850 캜 to 1000 캜.

In some embodiments of the present invention, the steel tube may comprise silicon (Si) in the range of 0.10 wt% to 0.25 wt%, manganese (Mn) in the range of 1.00 wt% to 1.60 wt%, 0.001 wt% to 0.03 wt% (P), 0.001 wt% to 0.02 wt% sulfur (S), and 0.001 wt% to 0.005 wt% boron (B).

In some embodiments of the present invention, the steel tube comprises chromium (Cr) in the range of 0.001 wt% to 0.05 wt%, molybdenum (Mo) in the range of 0.001 wt% to 0.05 wt%, and 0.001 wt% to 0.05 wt% And nickel (Ni) in the range of 1 to 100% by weight.

According to an aspect of the present invention, there is provided a method of manufacturing a hot-formed steel pipe, comprising: preparing a steel sheet containing carbon in a range of 0.22 wt% to 0.28 wt%; Molding the steel sheet into semicircular steel using a black down roll; Molding the semicircular steel into a quarry steel using a fin pass roll; Forming a steel pipe by welding the tubular steel material using a squeeze roll; Cutting the steel pipe to form an individual steel pipe; Heating the individualized steel pipe; Inserting the individualized steel pipe into a mold having a slow cooling region and a rapid cooling region in which the cooling fluid is injected in the quench region; And pressing the metal mold to the steel pipe to differentially cool the steel pipe by the cooling fluid to hot-mold the individualized steel pipe.

According to an aspect of the present invention, there is provided a hot-formed steel pipe formed by using the above-described method, wherein the hot formed steel pipe contains carbon in a range of 0.22 wt% to 0.28 wt% , Wherein in the hot-formed steel pipe, the portion slowly cooled by the slow-cooling region of the mold has a strength of 600 MPa to 800 MPa and an elongation of 12% to 16%, and in the hot-formed steel pipe, The quenched portion may have a strength of 1500 MPa to 1700 MPa and an elongation of 7% to 8%.

The method for manufacturing a hot-formed steel pipe according to the technical idea of the present invention performs hot forming of a steel pipe by using a metal mold having a slow cooling region and a quenching region and injecting a cooling fluid directly to the steel pipe. Therefore, in the same hot forming step, it is possible to simultaneously form the strengthened region by quenching and the softened region by slow cooling. Such a steel pipe can simultaneously achieve rigidity by the reinforced region and shock absorption by the softening region.

The effects of the present invention described above are exemplarily described, and the scope of the present invention is not limited by these effects.

1 is a flowchart illustrating a method of manufacturing a hot-formed steel pipe according to an embodiment of the present invention.
2 is a flowchart showing a method of manufacturing a hot-formed steel pipe according to an embodiment of the present invention.
3 to 6 are schematic views showing a method of manufacturing a hot-formed steel pipe of FIG. 2 according to an embodiment of the present invention, in accordance with process steps.
FIG. 7 is an iron-carbon state diagram illustrating a microstructure of a hot-formed steel pipe formed by the method of manufacturing a hot-formed steel pipe of FIG. 2 according to an embodiment of the present invention.
FIG. 8 is a schematic view showing a part to which a steel pipe manufactured by a steel pipe manufacturing method according to the technical idea of the present invention is applied.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It will be apparent to those skilled in the art that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. The scope of technical thought is not limited to the following examples. Rather, these embodiments are provided so that this disclosure will be more thorough and complete, and will fully convey the scope of the invention to those skilled in the art. As used herein, the term "and / or" includes any and all combinations of one or more of the listed items. The same reference numerals denote the same elements at all times. Further, various elements and regions in the drawings are schematically drawn. Accordingly, the technical spirit of the present invention is not limited by the relative size or spacing depicted in the accompanying drawings.

In the present specification, a steel pipe will be described as an example of a steel material applied to the technical idea of the present invention. However, this is illustrative and the technical idea of the present invention is not limited to this, and can be applied to various shapes of steel.

1 is a flowchart showing a method (S1) for manufacturing a hot-formed steel pipe according to an embodiment of the present invention, in accordance with an embodiment of the present invention. The sequence of the process steps of the manufacturing method of FIG. 1 is illustrative, and the process of being performed in a different order is also included in the technical idea of the present invention.

Referring to FIG. 1, a method S1 for manufacturing a hot-formed steel pipe may include various steps for forming a steel pipe from a plate-like raw material. Specifically, the manufacturing method (S1) of the steel pipe comprises a step (S2) of preparing a steel sheet as a raw material, a step (S3) of forming the steel sheet into a semicircular steel using a black down roll, A step S6 of forming a steel pipe by cutting the steel pipe to form an individual steel pipe; and a step S6 of forming an individual steel pipe by joining the steel pipe to the steel pipe by welding using a squeeze roll to form a steel pipe, And a step (S7) of hot-forming the individualized steel pipe.

The steel sheet as a raw material may be a hot rolled coil wound and rolled by a hot rolling process. Alternatively, the steel sheet may be an individual steel sheet. The thickness of the steel sheet may vary. The steel sheet may be formed into a steel pipe by various stages of molding, for example, a roll forming method may be used. However, this is merely exemplary and the technical idea of the present invention is not limited to this, and the steel sheet can be formed into a steel pipe by various methods.

The steel pipe may be made of the same alloy as the steel sheet as a raw material. The steel pipe may be composed of an iron alloy whose matrix is composed of iron, and may include various alloying elements.

In the step S2 of preparing the steel sheet, a hot-rolled coil having, for example, a hot-rolled sheet shape and wound as a coil is prepared. The steel sheet may have a rectangular cross section 2 as shown in Fig.

In the step (S3) of forming the steel sheet into a semicircular steel material by using a black down roll, the steel sheet is rolled between black down rolls to form a semicircular steel material. The semicircular steel may have a semicircular section 3 as shown in Fig.

In the step (S4) of forming the semicircular steel material into a quadrangular steel material by using a pin pass roll, the semicircular material is rolled between fin pass rolls and formed into a quadrangular steel material. The tubular steel may have a tubular section 4 as shown in Fig. The solid line in the section shows the contact points of both ends of the tubular steel material.

In the step S5 of forming the steel pipe by welding using the squeeze roll, the steel pipe may be formed by joining the steel pipe to each other while passing the sintered steel through the squeeze rolls. The steel pipe formed by such welding may have a tubular section 5 as shown in Fig. The welding can be performed in various ways, for example, electric resistance welding (ERW) using an induction coil method, or tungsten inert gas welding (TIG) using a gas welding method. The tubular steel may be locally heated by the induction coil before passing through the squeeze roll. Such heating may alleviate the thermal shock that may be caused to the quarry steel during the welding by the squeeze roll. After performing the welding step, the steel tube may be cooled using a liquid such as water or cooled using air.

In the step (S6) of cutting the steel pipe to form an individualized steel pipe, the steel pipe is cut to a desired length using a press device, a welding device, or a cutter to form the individualized steel pipe.

In the step (S7) of hot-forming the individualized steel pipe, the individualized steel pipe is inserted into a hot-forming die and pressurized, whereby the individualized steel pipe is hot-formed into a desired shape. The step of hot forming may further include a step of preheating the individualized steel pipe. Further, the hot forming step may be performed so as to have another structure formed by different cooling rates by press-molding the individualized steel pipe at different temperatures depending on the region.

Step S2 of preparing the steel sheet or step S7 of hot-forming the individualized steel pipe may be performed by a continuous process or by an intermittent process.

2 is a flowchart showing a method (S10) of manufacturing a hot-formed steel pipe according to an embodiment of the present invention. The flow chart of Fig. 2 may correspond to the step (S7) of hot-forming the steel pipe in the manufacturing method (S1) of the steel pipe of Fig.

3 to 6 are schematic views showing a method (S10) for manufacturing a hot-formed steel pipe of FIG. 2 according to an embodiment of the present invention, in accordance with process steps.

7 is an iron-carbon state diagram for explaining the microstructure of the hot-formed steel pipe formed by the method (S10) of the hot-formed steel pipe of FIG. 2 according to an embodiment of the present invention.

Referring to FIG. 2, the method (S10) of manufacturing a hot-formed steel pipe comprises heating a steel pipe (S20), inserting the steel pipe into a mold having a slow- A step S30 of pressing the metal mold to the steel pipe, a step of differentially cooling the steel pipe by the cooling fluid, and a step S40 of hot forming the steel pipe.

Referring to FIGS. 2 and 3, the step S20 of heating the steel pipe heats the steel pipe 10 in a heating furnace or the like. The heating may be performed in an air atmosphere, an inert gas atmosphere, or a vacuum atmosphere.

The steel pipe 10 may be a steel pipe formed by the method of FIG. However, this is illustrative and the technical idea of the present invention is not limited to this, and can be applied to metal products of various shapes. For example, a steel plate may be applied instead of the steel pipe 10.

The steel pipe 10 may include iron as a matrix and alloying various elements. The steel tube 10 may include, for example, carbon (C) in the range of about 0.22 wt% (weight ratio) to about 0.28 wt%, silicon (Si) in the range of about 0.10 wt% to about 0.25 wt%, about 1.00 wt% (P) in the range of from about 0.001 wt% to about 0.03 wt%, sulfur (S) in the range of from about 0.001 wt% to about 0.02 wt%, and from about 0.001 wt% to about 0.005 wt% lt; / RTI > (B). < RTI ID = 0.0 > For example, the steel pipe 10 may include manganese (Mn) and silicon (Si) so that the manganese (Mn) / silicon (Si) If it is outside the above range, a high melting point oxide due to manganese (Mn) and silicon (Si) may be generated.

In addition, the steel pipe 10 may include chromium (Cr) in the range of about 0.001 wt% to about 0.05 wt%, molybdenum (Mo) in the range of about 0.001 wt% to about 0.05 wt%, and about 0.001 wt% to about 0.05 wt% Of nickel (Ni). In addition, the steel pipe 10 may include chromium (Cr) in the range of about 0.001 wt% to about 0.01 wt%, molybdenum (Mo) in the range of about 0.001 wt% to about 0.01 wt%, and about 0.001 wt% to about 0.01 wt% Of nickel (Ni). Such chromium (Cr), molybdenum (Mo), and nickel (Ni) can perform the function of improving the hot forming property of the steel pipe 10 during hot forming.

The steel pipe 10 may be heated to a temperature higher than a temperature at which austenite (γ-Fe) is formed, and the steel pipe 10 may have an austenite microstructure due to such heating. The austenite forming temperature is a temperature above the A3 temperature line in Fig. 7, and the A3 temperature line may vary depending on the composition of carbon and other elements. For example, if the steel pipe 10 contains carbon (C) in the range of 0.22 wt% to about 0.28 wt%, it may have an austenite forming temperature in the range of about 800 ° C to 850 ° C. Accordingly, the steel pipe 10 can be heated to a temperature in the range of about 850 캜 to 1000 캜 to sufficiently generate the austenite transformation.

2 and 4, in step S30 of inserting the steel pipe into the metal mold, the heated steel pipe 10 is inserted into the metal mold 20. The mold 20 may have a slow cooling area and a rapid cooling area. Further, the mold 20 can be injected with the cooling fluid in the quenched region.

Hereinafter, the metal mold 20 for providing differential cooling to the steel pipe 10 will be described in detail.

The mold 20 is composed of a pair of molds capable of forming a desired molding shape, and may specifically include an upper mold 30 and a lower mold 60.

The upper mold 30 may include an upper base member 32 and may also include an upper slow mold member 40 and an upper quench mold member 50 mounted on the upper base member 32. [ The upper mold 30 is constituted by the upper gradual mold member 40 and the upper mold member 50 so as to provide differential cooling in which a part of the steel pipe 10 is quenched and the other part is slowly cooled.

The upper gradual mold release member 40 can provide a gradual cooling area where the steel pipe 10 is slowly cooled and thereby prevent the martensitic transformation in the portion of the steel pipe 10 in contact with the upper gradual mold member 40 .

The upper slow cooling mold member 40 may include an upper heating element 42. The upper heating element 42 may be composed of a heat wire or a ceramic heater. The upper heating element 42 can heat the upper gradual mold member 40 to a desired temperature and heat the upper slow releasing mold member 40 at a temperature higher than the martensitic transformation start temperature of the steel pipe 10 Can be maintained. The upper heating element 42 may heat the upper slow mold member 40 to a temperature of, for example, about 400 캜 or more. For example, the upper heating element 42 may maintain the upper slow mold member 40 at a temperature in the range of about 400 [deg.] C to about 450 [deg.] C. Alternatively, the upper heating element 42 may alternatively provide a temperature capable of heating the upper slow mold member 40 to a temperature in the range of about 850 캜 to 1000 캜, and then contacted with the upper slow mold member 40 It is possible to provide a temperature profile for cooling the upper slow releasing mold member 40 at a cooling rate at which martensitic transformation does not occur in the portion of the steel pipe 10. [

The upper slow mold member 40 may have a forming surface 48 for hot forming the steel pipe 10 on the surface in contact with the steel pipe 10. The shaping surface 48 may vary in various ways depending on the desired shape.

On the other hand, the upper quench mold member 50 can provide a quench zone in which the steel pipe 10 is quenched, thereby causing the martensitic transformation in the portion of the steel pipe 10 in contact with the upper quench mold member 50 .

The upper quench mold member 50 may include an upper cooling element 52. The upper cooling element 52 may consist of cooling water or a cooling water flow through which the cooling gas flows, or may be a cooling medium that provides cooling by an electrical method. The upper cooling element 52 can cool the upper rapid mold member 50 to a desired temperature and cool the upper rapid mold member 50 to a temperature lower than the martensitic transformation start temperature of the steel pipe 10 Can be maintained. The upper cooling element 52 can cool the upper quench mold member 50, for example, the upper slow mold member 40 to a temperature of, for example, about 400 캜 or below, for example, about room temperature (about 25 캜) have. In addition, the upper cooling element 52 is optional and may be omitted.

The upper quench mold member 50 may include an upper cooling fluid nozzle 54 that quenches the steel pipe 10 by injecting a cooling fluid to the steel pipe 10. The upper cooling fluid nozzle 54 may be exposed to the forming surface 58 of the upper quench mold member 50. The number and arrangement of the upper cooling fluid nozzles 54 can vary widely.

The cooling fluid may be directly sprayed from the upper cooling fluid nozzle 54 to the steel pipe 10 to quench the steel pipe 10. The cooling fluid may be a liquid or a gas. For example, the cooling fluid may comprise water and may have a temperature in the range of about 0 ° C to about 100 ° C. The cooling fluid may also be a gas such as air, nitrogen vapor, and the like, and may have a temperature ranging from about -100 ° C to about 400 ° C. In addition, the cooling fluid may comprise a liquefied gas, for example, liquid nitrogen.

The upper cooling fluid nozzle 54 may be connected to the upper cooling flow passage 56 and the upper cooling flow passage 56 may be connected to a cooling fluid reservoir (not shown) to supply the cooling fluid to the upper cooling fluid nozzle 54 have. Further, the upper cooling fluid nozzle 54 and the upper cooling flow passage 56 can cool the upper rapid cooling metal mold member 50.

In addition, the upper quench mold member 50 may have a forming surface 58 for molding the steel pipe 10 on the surface in contact with the steel pipe 10. The shaping surface 58 may vary in various ways depending on the desired shape. The shaping of the steel tube 10 by the shaping surface 58 may be limited relative to the shaping of the steel tube 10 by the shaping surface 48 since the shaping surface 58 is lower in temperature than the shaping surface 48. [ have.

Since the upper and lower cooling mold members 40 and 50 have different temperatures, the upper and lower cooling mold members 40 and 50 are spaced apart from each other in order to minimize mutual heat transfer. (34) may be disposed.

4 shows an arrangement in which the upper cooling mold member 50 is located at the center and the upper cooling mold member 40 is located at both ends of the upper cooling mold member 50. However, The technical idea is not limited to this. For example, an arrangement in which the upper gradual mold releasing member 40 is located at the center and the upper gradual mold member 50 is located at both ends is also included in the technical idea of the present invention. Also, for example, the arrangement in which the upper slow mold member 40 is located at one end and the upper mold member 50 is located at the other end is also included in the technical idea of the present invention. The technical idea of the present invention also encompasses a case where a plurality of upper slow cooling mold members 40 and a plurality of upper rapid mold members 50 are arranged in various orders.

The lower mold 60 may include a lower base member 62 and may also include a lower cooling mold member 70 and a lower cooling mold member 80 mounted on the lower base member 62. The lower mold 60 is constituted by the lower cooling mold member 70 and the lower cooling mold member 80 so that it is possible to provide differential cooling in which a part of the steel pipe 10 is quenched and the other part is slowly cooled.

The lower gradual mold member 70 can provide a slow cooling area in which the steel pipe 10 is slowly cooled to thereby prevent the martensitic transformation in the portion of the steel pipe 10 in contact with the lower gradual mold member 70 .

The lower gradual mold member 70 may include a lower heating element 72. The lower heating element 72 can heat the lower cooling mold member 70 to a desired temperature. The lower heating element 72 may have the same configuration as the upper heating element 42 described above and perform the same function.

The lower gradual mold member 70 may have a forming surface 78 for hot forming the steel pipe 10 on the surface in contact with the steel pipe 10. The shaping surface 78 may vary variously depending on the desired shape.

On the other hand, the lower quenching mold member 80 may provide a quench zone in which the steel pipe 10 is quenched, thereby causing the martensitic transformation in the portion of the steel pipe 10 in contact with the lower quench mold member 80 .

The lower quench mold member 80 may include a lower cooling element 82. The lower cooling element 82 can cool the lower quenching mold member 80 to a desired temperature. The lower cooling element 82 is optional and may be omitted. The lower cooling element 82 may have the same configuration as the upper cooling element 52 described above and perform the same function.

The lower quench mold member 80 may include a lower cooling fluid nozzle 84 that urges the cooling pipe 10 to quench the steel pipe 10. The lower cooling fluid nozzle 84 may be exposed to the forming surface 88 of the lower quenching mold member 80. The number and arrangement of the lower cooling fluid nozzles 84 can vary widely. The cooling fluid can be directly sprayed from the lower cooling fluid nozzle 84 to the steel pipe 10 to quench the steel pipe 10. The lower cooling fluid nozzle 84 may have the same configuration as the upper cooling fluid nozzle 54 described above and perform the same function.

The lower cooling fluid nozzle 84 may be connected to the lower cooling flow passage 86 and the lower cooling flow passage 86 may be connected to a cooling fluid reservoir (not shown) to supply the cooling fluid to the lower cooling fluid nozzle 84 have. Further, the lower cooling fluid nozzle 84 and the lower cooling passage 86 can cool down the lower quenching mold member 80.

In addition, the lower quenching mold member 80 may have a forming surface 88 for molding the steel pipe 10 on the surface in contact with the steel pipe 10. The shaping surface 88 may vary in various ways depending on the desired shape. The forming of the steel pipe 10 by the forming surface 88 may be limited relative to the forming of the steel pipe 10 by the forming surface 78 since the forming surface 88 is lower in temperature than the forming surface 78. [ have.

Since the lower cooling mold member 70 and the lower cooling mold member 80 have different temperatures from each other, the lower cooling mold member 70 and the lower cooling mold member 80 are separated from each other by the grooves that separate the lower cooling mold member 70 and the lower cooling mold member 80, (64) may be disposed.

4 shows an arrangement in which the lower rapid mold member 80 is positioned at the center and the lower mold 50 is located at both ends of the lower mold member 80. However, The technical idea is not limited to this.

2 and 5, in the step S40 of hot-forming the steel pipe, the metal mold 20 is contacted with the steel pipe 10 and pressed. At the same time, the steel pipe 10 is subjected to differential cooling by the cooling fluid to hot-mold the steel pipe 10.

The steel pipe 10 can contact the upper mold 30 and the lower mold 60 and can be molded under pressure. A part of the steel pipe 10 is in contact with the slow cooling area of the mold 20 to prevent martensite transformation and another part of the steel pipe 10 is in contact with the quenching area of the mold 20 to cause martensitic transformation.

The first region 12 of the steel pipe 10 may be pressed and cooled while being compressed between the upper and lower slow mold members 40 and 70. The upper and lower cooling mold members 40 and 70 may be heated by the upper heating element 42 and the lower heating element 72 respectively and may be heated above a temperature that prevents the formation of martensite have. The upper slow mold member 40 and the lower slow mold member 70 may be heated to a temperature of, for example, about 400 캜 or higher, for example, and maintained at a temperature in the range of about 400 캜 to about 450 캜.

Martensite transformation can be suppressed in the first region 12 of the steel pipe 10 and the first region 12 of the steel pipe 10 can have a ferrite structure or a ferrite structure, And may have a pearlite mixed structure.

The second region 14 of the steel pipe 10 may be pressed and quenched between the upper and lower quenching mold members 50 and 80 to be molded. The cooling fluid is directly jetted from the mold 20 to the steel pipe 10 in the second region 14 of the steel pipe 10 to quench the second region 14 of the steel pipe 10 to generate martensite transformation . A part of the metal mold 20 maintained at a temperature causing martensite transformation is brought into contact with the second region 14 of the steel pipe 10 to cause martensite transformation in the second region 14 of the steel pipe 10 .

The upper quench mold member 50 and the lower quench mold member 80 can be cooled by the upper cooling element 52 and the lower cooling element 82 and can be cooled and maintained at a temperature causing martensite transformation . The upper quench mold member 50 and the lower quench mold member 80 can be cooled to a temperature of, for example, about 400 캜 or lower, for example, a normal temperature (about 25 캜). The second region 14 of the steel pipe 10 can be quenched as the upper and lower rapid mold members 50 and 80 are cooled.

In addition, the cooling fluid can be directly sprayed from the upper cooling fluid nozzle 54 and the lower cooling fluid nozzle 84 to the steel pipe 10 to cool the steel pipe 10. The cooling fluid may be liquid or gaseous, and may comprise water having a temperature in the range, for example, from about 0 ° C to about 100 ° C.

Martensitic transformation may occur in the second region 14 of the steel pipe 10 and the second region 14 of the steel pipe 10 may have a martensite structure.

Referring to Fig. 6, the mold 20 is removed from the steel pipe 10 to complete the hot-formed steel pipe 10.

The steel pipe 10 may have multiple structures due to differential cooling. That is, the steel pipe 10 is slowly cooled and is quenched with a first region 12 having a low strength and a high elongation and having a ferrite and a pearlite structure, and has a high strength and a low elongation, And a second region 14, Further, between the first region 12 and the second region 14, the third region 16, which is a transition region having the intermediate structure and intermediate strength and elongation characteristics, may be located.

For example, the first region 12 of the steel pipe 10 is a portion slowly cooled by the slow cooling region of the mold 20, having a strength of about 600 MPa to about 800 MPa and an elongation of about 12% to about 16% Lt; / RTI > The second region 14 of the steel pipe 10 may have a strength quenched by the quench region of the mold 20 of from about 1500 MPa to about 1700 MPa and an elongation of from about 7% to about 8%.

The technical idea of the present invention is applicable to steel plates or steel pipes, and it is applicable to other types of steels and also to other metals.

For example, when the steel pipe 10 is a steel plate, all of the surfaces of the steel plate may be contacted with the mold during hot forming so as to be slowly cooled or quenched. Further, the quenching effect can be increased by injecting the cooling fluid directly to the steel sheet.

For example, when the steel pipe 10 is a steel pipe, it may be difficult to slowly cool or quench all of the surfaces of the steel pipe during hot forming by bringing them into contact with the metal mold. That is, since the steel pipe has a circular surface, it can be difficult or uneconomical to manufacture a mold that contacts both of the circular surfaces. Therefore, it may be difficult to uniformly quench the steel pipe with only the mold. However, it is possible to realize uniform quenching by injecting the cooling fluid directly to the steel plate separately from or together with the cooling by the mold, and also to increase the quenching effect.

The steel pipe 10 can be applied to products of various technical fields, and can be applied to, for example, automobile parts. The strength and elongation of the steel pipe 10 can vary in various ways, and the carbon content can be varied in various ways. For example, steel tubes containing carbon in the range of about 0.22 wt% to about 0.28 wt% can be applied to compact cars. Steel pipes containing from about 0.28 wt.% To about 0.32 wt.% Carbon are applicable to medium-sized vehicles. Steel pipes containing carbon in the range of about 0.32 wt% to about 0.38 wt% are applicable to large vehicles.

FIG. 8 is a schematic view showing a part to which a steel pipe manufactured by a steel pipe manufacturing method according to the technical idea of the present invention is applied. Fig. 8 shows an example in which a steel pipe is applied, and the technical idea of the present invention is not limited to such a steel pipe.

8, a steel tube according to the technical idea of the present invention includes a bumper beam 100, a door beam 200, a pillar beam 300, A lower stiffener 400 or the like.

For example, the bumper beam 100 may have a strengthened region 110 formed by quenching in the central portion and a softened region 120 formed by slow cooling at both ends of the strengthened region 110. Accordingly, in the event of a vehicle collision, it is possible to realize rigidity securing by the reinforcement region 110 and realize shock absorption by the softening region 120.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the appended claims. Will be apparent to those of ordinary skill in the art.

10: steel pipe, 20: mold, 30: upper mold, 32: upper base member, 34:
40: upper slow cooling mold member, 42: upper heating element, 48: molding surface,
50: upper cooling mold member, 52: upper cooling element,
54: upper cooling fluid nozzle, 56: upper cooling flow passage, 58: molding surface,
60: lower mold, 62: lower base member, 64: groove,
70: lower cooling mold member, 72: lower heating element, 78: molding surface,
80: a lower quenching mold member, 82: a lower cooling element,
84: lower cooling fluid nozzle, 86: lower cooling channel, 88: molding surface,
100: bumper beam, 200: door beam, 300: pillar beam, 400: lower stiffener,

Claims (10)

Heating a steel pipe containing carbon in the range of 0.22 wt% to 0.28 wt%;
Inserting the steel pipe into a mold having a slow cooling region and a quenching region and through which a cooling fluid is injected in the quenching region; And
Compressing the metal mold to the steel pipe, differentially cooling the steel pipe by the cooling fluid, and hot-forming the steel pipe;
And forming a hot-formed steel pipe. The method according to claim 1,
The step of hot-forming the steel pipe comprises:
Wherein the cooling fluid supplied through the cooling channel formed in the mold is directly sprayed from the mold to a part of the steel pipe to quench a part of the steel pipe to generate martensite transformation. The method according to claim 1,
The step of hot-forming the steel pipe comprises:
Wherein a part of the metal kept at a temperature causing martensitic transformation is brought into contact with a part of the steel pipe to cause martensitic transformation in a part of the steel pipe. The method according to claim 1,
The step of hot-forming the steel pipe comprises:
A part of the steel pipe is in contact with the slow cooling area of the mold to prevent martensite transformation,
And another part of the steel pipe is in contact with the quenching area of the mold to cause martensitic transformation. The method according to claim 1,
Wherein the cooling fluid comprises water in the range of 0 占 폚 to 100 占 폚. The method according to claim 1,
Wherein the heating step heats the steel pipe at a temperature in the range of 850 캜 to 1000 캜. The method according to claim 1,
Wherein the steel tube comprises silicon (Si) in the range of 0.10 wt% to 0.25 wt%, manganese (Mn) in the range of 1.00 wt% to 1.60 wt%, phosphorus in the range of 0.001 wt% to 0.03 wt%, 0.001 wt% 0.02 wt% sulfur (S), and 0.001 wt% to 0.005 wt% boron (B). 8. The method of claim 7,
Wherein the steel pipe comprises at least one of chromium (Cr) in a range of 0.001 wt% to 0.05 wt%, molybdenum (Mo) in a range of 0.001 wt% to 0.05 wt%, and nickel (Ni) in a range of 0.001 wt% to 0.05 wt% Further comprising the steps of: Preparing a steel sheet containing carbon in a range of 0.22 wt% to 0.28 wt%;
Molding the steel sheet into semicircular steel using a black down roll;
Molding the semicircular steel into a quarry steel using a fin pass roll;
Forming a steel pipe by welding the tubular steel material using a squeeze roll;
Cutting the steel pipe to form an individual steel pipe;
Heating the individualized steel pipe;
Inserting the individualized steel pipe into a mold having a slow cooling region and a rapid cooling region in which the cooling fluid is injected in the quench region; And
Compressing the metal mold to the steel pipe, differentially cooling the steel pipe by the cooling fluid, and hot-forming the individualized steel pipe;
And forming the hot-formed steel pipe. A hot-formed steel pipe formed by the method according to any one of claims 1 to 9,
The hot-formed steel pipe comprises carbon in a range of 0.22 wt% to 0.28 wt%
In the hot-formed steel pipe, the portion slowly cooled by the slow-cooling region of the mold has an intensity of 600 MPa to 800 MPa and an elongation of 12% to 16%
In the hot-formed steel pipe, the quenched portion of the mold by the quench region has an intensity of 1500 MPa to 1700 MPa and an elongation of 7% to 8%.
KR1020120143744A 2012-12-11 2012-12-11 Hot forming steel pipe having multi-microstructure due to different cooling and method of manufacturing the same KR20140075954A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101865737B1 (en) * 2016-08-17 2018-06-08 기아자동차 주식회사 Hot stamping device that pre cooles blank befor forming
CN114042794A (en) * 2021-11-17 2022-02-15 宁波江丰热等静压技术有限公司 Forming method of titanium-containing metal curved plate

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101865737B1 (en) * 2016-08-17 2018-06-08 기아자동차 주식회사 Hot stamping device that pre cooles blank befor forming
CN114042794A (en) * 2021-11-17 2022-02-15 宁波江丰热等静压技术有限公司 Forming method of titanium-containing metal curved plate
CN114042794B (en) * 2021-11-17 2024-02-06 宁波江丰热等静压技术有限公司 Forming method of titanium-containing metal curved plate

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