Plated steel sheet for hot press forming, hot press-formed member, hot press-formed parts, manufacturing methods therefor, forming device, forming method, battery case bracket, and battery pack module

Abstract

One aspect of the present invention relates to a steel suitable for hot press forming and, more specifically, to an aluminum-based plated steel sheet for hot press forming, a hot press-formed member and manufacturing methods therefor. In addition, another aspect of the present invention relates to: a forming device for forming a high-strength steel; a forming method; a battery case bracket formed thereby; and a battery pack module.

Description

Hot press-formed galvanized steel sheets, hot press-formed members, hot press-formed parts and their manufacturing methods, forming devices, forming methods, brackets for battery cases and battery pack modules

[0001] One aspect of the present invention relates to steel suitable for hot press forming, and more specifically, to a plated steel sheet for hot press forming, a hot press forming member, a hot press forming part, and a method for manufacturing the same. In addition, another aspect of the present invention relates to a forming device for forming high-strength steel, a forming method, and a bracket for a battery case formed thereby, and further, a battery pack module.

[0002] The demand for lightweight vehicles and improved safety is driving the active adoption of high-strength steel. Recently, due to the depletion of petroleum resources and growing environmental concerns, regulations on improving automobile fuel efficiency are becoming increasingly stringent. From a material perspective, reducing the thickness of steel sheets used in vehicles is one way to improve fuel efficiency. However, reducing thickness can compromise vehicle safety, so increasing the strength of steel sheets is essential.

[0003] For these reasons, demand for high-strength steel plates has persisted, and various types have been developed. However, due to their inherently high strength, these steel plates suffer from poor workability. Specifically, because the product of strength and elongation tends to remain constant across steel grades, increasing strength leads to a decrease in elongation, a key indicator of workability.

[0004] To address these issues, hot press forming has been proposed. Hot press forming involves processing steel plates at high temperatures, ideal for machining, and then rapidly cooling them to lower temperatures. This process creates low-temperature structures, such as martensite, within the steel plate, thereby enhancing the strength of the final product. This approach has the advantage of minimizing workability issues when manufacturing high-strength components.

[0005] Hot press forming is a processing method that manufactures high-strength molded parts by heating a blank, forming the heated blank into a desired shape through press forming, and cooling the blank while keeping the mold closed.

[0006] This hot press forming method, when using a hot press forming method that forms at high temperatures, has the excellent characteristic of having an elongation of over 50% at the high temperature where forming is performed, so even parts with a small curvature radius can be formed without cracks, and it is possible to secure the shape of the formed part that cannot be secured with cold ultra-high strength. In addition, hot press formed parts manufactured by hot working (hot stamping) a blank can be formed at high temperatures with excellent general formability, so parts with various shapes can be manufactured compared to typical giga-grade cold formed materials.

[0007] However, in the case of the hot press forming method described above, there was a problem in that the steel sheet surface was oxidized because it was heated to a high temperature, and therefore a process for removing the oxide on the steel sheet surface had to be added after the press forming. Patent Document 1 was proposed as a method for solving this problem. In Patent Document 1, a steel sheet plated with aluminum was used in a process of heating and rapidly cooling after hot press forming or room temperature forming (briefly referred to as 'post-heat treatment'), and since the aluminum plating layer exists on the surface of the steel sheet, the steel sheet does not oxidize when heated.

[0008] However, when an aluminum plating layer is formed on the surface and then heated, problems such as the aluminum plating layer melting and contaminating the equipment may occur depending on the heating rate. Furthermore, in the case of high-strength components, the problem of so-called hydrogen delayed fracture may occur, in which hydrogen trapped within the steel sheet accumulates and leads to the destruction of the component.

[0009] One way to solve this problem has been proposed, which involves heating an aluminum-plated steel sheet before heating to form an aluminum-iron alloy layer on the steel sheet, and then using the steel sheet with the aluminum-iron alloy plating layer formed thereon for hot press forming. That is, if the plating layer is alloyed at a relatively low temperature range before heating for hot press forming, even if heating is performed at a relatively rapid rate, the aluminum is already alloyed, so problems caused by aluminum melting can be prevented even if heated to a temperature higher than the melting point of aluminum. In addition, in the case of a pre-alloyed plating steel sheet, it can have an alloy layer on the surface that facilitates the release of hydrogen, which can have the effect of reducing the possibility of hydrogen delayed fracture.

[0010] Meanwhile, when applying a plated steel sheet as a material for hot press forming, the plated steel sheet must have sufficient formability, and thus, it is possible to improve the paint adhesion of the hot press formed part obtained by hot press forming.

[0011] Therefore, there is a need to develop a method to improve the high-temperature formability of galvanized steel sheets for hot press forming.

[0012] Meanwhile, battery systems used in electric vehicles use battery cases to protect the battery cells inside, and these battery cases must ensure crash safety performance and watertightness.

[0013] Battery cases for electric vehicles are typically made from expensive aluminum extrusions or sheets, but efforts are being made to use steel, which offers competitive pricing and is easily recyclable. However, high-strength steel suffers from poor formability, making it difficult to form into the desired shape.

[0014] High-strength steel is often used only in simple, straight-section parts formed through roll forming. When manufacturing battery cases using these straight parts, alignment issues arise due to thin steel sheets and springback within the parts, making butt welding difficult at the corners where two straight parts meet.

[0015] To overcome this issue, a separate component (a bracket) can be used to support the two straight parts by wrapping around the corresponding corner area. This component has a longitudinal bend that reflects the required corner angle and also has a flange shape that connects to the upper and lower plates of the battery pack, making it difficult to mold.

[0016] FIG. 1 is a schematic diagram of a side frame of a battery case, and FIG. 2 is a cross-sectional view taken along line AA' of FIG. 1. As shown in FIGS. 1 and 2, the side frame (A-1) of the battery case must have flanges formed at the upper and lower portions of the frame (A-10) in order to be connected to the upper and lower portions, and the same applies to the bracket (A-20). That is, the bracket (A-20) also includes a main body (A-23) and flanges (A-21, A-22) formed by bending from the main body (A-23). ​​The bracket (A-20) is difficult to form because it includes a curved portion having a radius of curvature (R1) and a curved surface having a radius of curvature (R2) in order to form flanges at the upper and lower portions.

[0017] When a part includes a curvature or dimensional transition, a stretch flange or a shrink flange is formed on the flange (A-21, A-22) depending on the geometric characteristics of the area. Furthermore, both types of flanges may form simultaneously, with one type dominating. In the stretch flange area, where thickness reduction is involved, necking, a localized reduction in cross-sectional area due to plastic instability, and subsequent fracture may occur if the molding amount is excessive or the material formability is insufficient compared to the required shape of the part. Meanwhile, in the shrink flange area, increased in-plane compressive load can lead to increased thickness, buckling, and wrinkles. These wrinkles and folds can create uneven gaps in the battery pack, potentially compromising its watertightness.

[0018] Meanwhile, in the case of the bracket (A-20), in order to ensure uniformity of strength and collision safety performance, it must be formed of the same material as the frame (A-10), which is a straight part. However, when forming with high-strength steel, there is a problem that it is extremely difficult to form a flange with a curved part.

[0019] In the case of conventional cold forming steel plates, when the tensile strength is 980 MPa or higher, the risk of wrinkles and fractures increases due to the high strength and insufficient ductility of the material, making it difficult to process curved flanges. Therefore, the use of press-hardened steel as a substitute is increasing.

[0020] Press-hardened steel is formed at high temperatures, resulting in low strength and high ductility at the time of forming, enabling it to be formed into complex shapes. However, because it must be formed in one pass while maintaining high temperatures, it is difficult to apply blank holders or drawbeads, which are used to control fracture and wrinkles, limiting the freedom of forming methods.

[0021] In addition, high-strength steel generally has a problem in that it cannot form parts with a small curvature radius due to its poor bendability, but recently, due to the issues of vehicle weight reduction and safety improvement in electric vehicles, etc., there is a need for molded parts that have high strength but a small curvature radius compared to existing ones, making it easier to utilize space.

[0022] Meanwhile, the hot press forming method has the problem that it cannot be formed sequentially through multiple mold stages as is done in cold forming because the high-temperature material heated in the furnace must be formed before it cools in the air. This drawback also makes it difficult to form parts with multiple hat shapes using the hot press forming method. While it is possible to form each part separately and then attach them together during the assembly stage, this method has the problem of increasing performance and process costs due to the separate forming of each part.

[0023] (Patent Document 1) U.S. Patent No. 6296805

[0024] (Patent Document 2) U.S. Patent Publication No. 2014-0056754

[0025] (Patent Document 3) Korean Patent Publication No. 10-2020-006635

[0026] (Patent Document 4) Korean Patent Publication No. 10-2023-0092430

[0027] The first aspect of the present invention is to provide an aluminum-based plated steel sheet for hot press forming, a plated steel sheet having excellent hot formability at high temperatures, a hot-formed member obtained by hot-forming the plated steel sheet, and a method for manufacturing the same.

[0028] A second aspect of the present invention is to provide a molding device capable of molding a bracket in which a flange and a curved portion are formed, a molding method, and a bracket manufactured thereby.

[0029] A third aspect of the present invention is to provide a molded part having a high tensile strength and a small radius of curvature compared to existing parts, or a battery pack module including the same.

[0030] A fourth aspect of the present invention is to provide a press-formed part and a manufacturing method thereof in which damage such as cracks is minimized during hot press forming to manufacture a part having a plurality of hat shapes.

[0031] The objectives of the present invention are not limited to the above-described matters. Additional objectives of the present invention are described throughout the specification, and those skilled in the art will have no difficulty understanding the additional objectives of the present invention from the contents described in the specification.

[0032] Hereinafter, the technical solutions of the present invention will be described. Although not essential, it should be noted that the technical solutions according to each aspect of the present invention can be usefully applied to the technical solutions of other aspects. For example, the hot-forming steel and / or manufacturing method according to the first aspect of the present invention can be usefully applied to the hot-formed members according to the second to sixth aspects, various parts obtained therefrom, and manufacturing methods thereof. In addition, the manufacturing methods of the parts according to the second and third aspects of the present invention, or the heat treatment conditions used therein, can be usefully applied in the process of manufacturing brackets or molded parts for battery cases according to the fourth to sixth aspects. Furthermore, the compositions and various useful parameters according to each aspect of the present invention can be appropriately combined with other aspects to obtain advantageous effects.

[0033] According to a first aspect of the present invention, a hot press forming plated steel sheet comprising a base steel sheet and an aluminum-based plated layer on one or both sides of the base steel sheet can be provided.

[0034] In one embodiment of the present invention, the plated steel sheet for hot press forming may have a maximum roughness (Rt) of a plated layer surface of 4.0 to 25.0 µm and a peak number per unit length (RPc) of 30 to 90 peaks / cm.

[0035] In addition, according to one embodiment of the present invention, the relationship between the amount of adhesion of the plating layer and the Rt can satisfy the following relational expression 1.

[0036] [Relationship 1]

[0037] 27.0 ≤ (ⓒ / 3)+(Rt / 2) ≤ 38.0

[0038] (The unit of relational expression 1 is ㎛, and ⓒ represents the amount of plating adhesion.)

[0039] In this way, a hot press-formable coated steel sheet having a surface-controlled plating layer can exhibit excellent high-temperature formability during the high-temperature heating process for hot press forming. Furthermore, a hot press-formable part obtained by hot press-forming such a hot press-formable coated steel sheet exhibits excellent paint adhesion and frictional properties.

[0040] In one embodiment of the present invention, the aluminum-based plating layer may have a composition including, in wt%, silicon (Si): 5.0 to 11.0%, iron (Fe): 10.0% or less, the remainder aluminum (Al), and other unavoidable impurities.

[0041] In one embodiment of the present invention, the steel sheet contains, in wt%, carbon (C): 0.02 to 0.60%, silicon (Si): 0.001 to 2.000%, aluminum (Al): 0.001 to 1.000%, manganese (Mn): 0.1 to 4.0%, phosphorus (P): 0.050% or less, sulfur (S): 0.0200% or less, nitrogen (N): 0.0200% or less, titanium (Ti): 0 to 1.0000%, niobium (Nb): 0 to 1.0000%, vanadium (V): 0 to 1.0000%, boron (B): 0 to 0.0100%, chromium (Cr): 0 to 1.00%, molybdenum (Mo): 0 to 1.00%, tungsten (W): 0 to 1.00%, copper (Cu): It may have a composition containing 0~1.0%, nickel (Ni): 0~1.0%, antimony (Sb): 0~1.00%, tin (Sn): 0~1.00%, calcium (Ca): 0~0.10%, magnesium (Mg): 0~0.10%, cobalt (Co): 0~1.00%, arsenic (As): 0~1.00%, zirconium (Zr): 0~1.00%, bismuth (Bi): 0~1.00%, rare earth elements (REM): 0~0.3%, the remainder being iron and other unavoidable impurities.

[0042] According to another aspect of the present invention, a method for manufacturing a plated steel sheet for hot press forming can be provided, comprising the steps of: preparing a base steel sheet; forming an aluminum-based plated layer on one or both sides of the base steel sheet to obtain a plated steel sheet; and subjecting the plated steel sheet to temper rolling.

[0043] In one embodiment of the present invention, the temper rolling treatment can be performed with a rolling force of 100 to 500 tons using a roll having a surface of Rt: 2 to 8 μm and RPc: 46 to 120 peak / cm.

[0044] By this method, a plated steel sheet for hot press forming with a controlled plated layer surface can be obtained.

[0045] In one embodiment of the present invention, the step of forming an aluminum-based plating layer to obtain a plated steel sheet may be a process performed by immersing a base steel sheet in an Al-based plating bath containing, by weight %, Si: 5.0 to 11.0%, Fe: 4.0% or less, the remainder Al, and other unavoidable impurities. Here, the base steel sheet may have the aforementioned alloy composition.

[0046] In one embodiment of the present invention, a step of performing alloying treatment by heating the plated steel sheet having an aluminum-based plated layer formed thereon in a temperature range of 670 to 900°C may be further included.

[0047] According to another aspect of the present invention, a hot press-formed member can be provided, which includes a base steel plate and an aluminum-based plating layer having a thickness (T) of 30.0 to 50.0 μm formed on the base steel plate.

[0048] In one embodiment of the present invention, the surface of the plating layer of the hot press-formed member may have a maximum roughness (Rt) of 6.0 to 26.0 μm and a peak number per unit length (RPc) of 60 to 130 peaks / cm.

[0049] In one embodiment of the present invention, the relationship between the thickness of the plating layer of the hot press-formed member and Rt can satisfy the following relational expression 2.

[0050] [Relationship 2]

[0051] 40.0 ≤ T + (Rt / 2) ≤ 57.0

[0052] (The unit of equation 2 is ㎛, and T represents the thickness of the plating layer.)

[0053] Such hot press-formed parts have excellent paint adhesion and frictional properties, and in one embodiment of the present invention, the friction coefficient of the parts may be 0.50 or less.

[0054] In one embodiment of the present invention, the aluminum-based plating layer of the hot press-formed member may be formed of an Al-Fe alloy in which the sum of the contents of Al and Fe is 89 wt% or more by alloying during the hot press-formed process.

[0055] Although not essential, the steel plate or hot-formed member according to the first aspect of the invention can secure improved performance when combined with the advantageous features of the other aspects described below.

[0056] A second aspect of the present invention comprises: a pad; a die disposed outside the first direction of the pad; And a punch including a body having a punch forming portion formed therein, the punch forming portion including a first punch forming portion having a straight first punch forming portion, a second punch forming portion having a curved second punch forming portion having a forming portion curvature radius (Rp), and a third punch forming portion having a straight third punch forming portion, when viewed in the first direction, the first to third punch forming portions being continuously arranged along a second direction perpendicular to the first direction on a horizontal plane, the first to third punch forming portions including first to third extension surface forming portions having a plane perpendicular to the first direction on both sides of the first direction, first to third body forming portions having a plane facing the pad, and first to third curved surface forming portions having a bending curvature radius (r) between the extension surface forming portion and the body forming portion, the pad including a pressing surface corresponding to the first to third body forming portions, and the die including, when viewed in the first direction, A forming device comprising a first die forming portion having a straight shape, a second die forming portion having a curved shape having a die curvature radius (Rd), and a third die forming portion having a straight shape, wherein the first to third die forming portions are arranged continuously along a second direction, and when the third body forming portion and the upper position of the third die forming portion are positioned on the same plane, the first body forming portion is positioned above the upper position of the first die forming portion when viewed in the first direction.

[0057] According to one embodiment of the present invention, there is an effect that enables forming of steel with poor formability (e.g., high-strength steel).

[0058] In one embodiment of the present invention, the punch further includes fourth and fifth punch forming portions symmetrical to the second and first punch forming portions with the third punch forming portion as the center, the die further includes fourth and fifth die forming portions symmetrical to the second and first die forming portions with the third die forming portion as the center, and the pressing surface of the pad may also include a surface corresponding to the main body forming portion of the fourth and fifth punch forming portions.

[0059] In one embodiment of the present invention, the punch may include a support member that supports the pre-molding material outside the first and fifth molding members with the third punch molding member as the center.

[0060] In one embodiment of the present invention, the curvature radius (Rp) of the molded portion may be smaller than the curvature radius (Rd) of the die.

[0061] In one embodiment of the present invention, the second direction length (lp) of the third body forming portion may be longer than the second direction length (ld) of the third die forming portion.

[0062] In one embodiment of the present invention, when viewed in the first direction, the center of the die curvature radius (Rd) in the second direction coincides with the center of the third body forming portion, and when viewed in the first direction, the angle (θ) at which the extension lines of imaginary tangents at both ends of the second and fourth punch forming portions intersect may be between 95 and 135°.

[0063] In one embodiment of the present invention, the first to fifth die forming portions include first to fifth die curved forming portions formed into a curved surface at a position relatively close to the punch in the first direction, and first to fifth flat forming portions formed at a position relatively far from the punch, and the curved surfaces of the first to fifth die curved forming portions increase in height as they get closer to the punch, and when the upper positions of the third body forming portion and the third die forming portion are positioned on the same plane, at least a portion of the second body forming portion may be positioned lower than the upper position of the second die forming portion when viewed in the first direction.

[0064] In one embodiment of the present invention, at least one of the punch and the die may include a cooling channel therein, and the curvature radius (Rp) of the forming portion and the bending curvature radius (r) may satisfy 25 mm ≤ Rp (mm) + r (mm) ≤ 30 mm.

[0065] Another aspect of the present invention provides a material forming method, comprising: a material forming step of forming a material longer in a first direction than a punch having a forming portion on the punch; a first forming step of forming the material into the shape of a main body forming portion of the punch through a pad positioned on the upper portion of the punch; and a second forming step of forming the material along the shape of the forming portion of the punch through a die positioned outside the pad in the first direction; wherein in the second forming step, the die forms an edge portion, a center portion, and an intermediate portion between the center and the edge of the material in that order in a second direction perpendicular to the first direction and the up-down direction.

[0066] In one embodiment of the present invention, the molding part includes, when viewed in the first direction, a first molding part having a straight shape, a second molding part having a curved shape having a curvature radius (Rp) of the molding part, a third molding part having a straight shape, a fourth molding part having a curved shape having a curvature radius (Rp) of the molding part, and a fifth molding part having a straight shape, and the middle part of the die is formed as a curved surface having a die curvature radius (Rd), and the die curvature radius (Rd) may be larger than the curvature radius (Rp) of the molding part.

[0067] In one embodiment of the present invention, the material is a steel plate, and the material settling step is performed while the material is heated to a temperature higher than AC3 of the material, and a cooling step may further be included in which the material is cooled to have a martensite structure by at least one of the punch and the die.

[0068] In one embodiment of the present invention, the material may be the aforementioned hot press forming coated steel sheet, or a hot forming member obtained by hot forming the aforementioned hot press forming coated steel sheet. As an example, the hot press forming coated steel sheet and the hot forming member may have the aforementioned alloy composition and may be manufactured by the aforementioned manufacturing method.

[0069] In one embodiment of the present invention, in the material settling step, the material may include a notch formed in the first direction toward the center of the material at a position corresponding to the middle portion of the die.

[0070] In one embodiment of the present invention, the first to fifth molding portions include first to fifth extension surface molding portions on a surface perpendicular to the first direction on both sides of the first direction, first to fifth body molding portions on a surface facing the pad, and first to fifth curved surface molding portions having a bending radius of curvature (r) between the extension surface molding portions and the body molding portions, and the bending radius of curvature (Rp) of the molding portion and the bending radius of curvature (r) can satisfy 25 mm ≤ Rp (mm) + r (mm) < 30 mm, 3 mm ≤ r (mm) ≤ 10 mm.

[0071] Another aspect of the present invention provides a bracket for a battery case including a molding surface having a molded portion having a curvature radius (Rp), wherein the molding surface includes: a main body; a flange extending and bending from an end of the main body; and a curved surface connected between the main body and the flange having a bending curvature radius (r); wherein the bracket is formed of a steel material including boron having a tensile strength of 1200 MPa or more and has a martensite structure, and the molded portion having a curvature radius (Rp) and the bending curvature radius (r) satisfy 25 mm ≤ Rp (mm) + r (mm) ≤ 30 mm, 3 mm ≤ r (mm) ≤ 10 mm.

[0072] In one embodiment of the present invention, the minimum thickness (tmin) and the initial thickness (tini) before forming in the flange can satisfy (tini - tmin) / tini ≤ 0.2, and the maximum thickness (tmax) and the initial thickness (tini) before forming in the curved surface can satisfy (tini - tmax) / tini ≥ -0.4.

[0073] In one embodiment of the present invention, the bracket may have an angle (θ) at which the extension lines of the virtual contacts at both ends of the molding surface intersect each other between 95 and 135°.

[0074] A bracket for a battery case according to one embodiment of the present invention can be manufactured using the molding method described above.

[0075] According to one embodiment of the present invention, the weight reduction, watertightness, and collision safety performance of the battery pack can be secured through the bracket manufactured using the molding method described above.

[0076] Although not necessarily essential, the article according to the second aspect of the invention may achieve further improved performance by combining it with the advantageous features of the other aspects described below.

[0077] A third aspect of the present invention provides a high-strength steel hot press-formed part comprising a first wall extending in a first direction, a second wall extending in a direction intersecting the first wall, and a third wall extending in the first direction and extending in a direction intersecting the second wall, a curved portion is formed between the first wall and the second wall, and the first wall, the second wall, and the curved portion are integrally formed, and the following relational expression 3 is satisfied.

[0078] [Relationship 3]

[0079] Wall height (hw) ≤ 13.4 * wall angle (θw) + 182.4

[0080] (Here, the wall height (hw) is the length from the first wall to the third wall in a direction perpendicular to the first direction, and the unit is mm; the wall angle (θw) is the angle between an arbitrary line perpendicular to the first direction and the second wall, and the unit is degree; the left and right sides are calculated by dimensionlessly converting them.)

[0081] In one embodiment of the present invention, the high-strength steel may be the hot press forming galvanized steel sheet described above.

[0082] According to one embodiment of the present invention, a molded part having high tensile strength and small curvature can be provided.

[0083] In one embodiment of the present invention, the first wall, the second wall, and the curved portion may be integrally formed by processing a plate material. In addition, the first wall, the second wall, and the curved portion may be integrally formed by processing a plate material, and the radius of curvature (r) of the curved portion may be greater than or equal to 0.5 mm, and the ratio (r / t) of the thickness (t) of the plate material to the radius of curvature (r) may be less than 2.5.

[0084] In one embodiment of the present invention, the molded part may have a tensile strength of 1300 to 2100 MPa.

[0085] In one embodiment of the present invention, the third wall and the fourth wall are parallel to the first direction, and the fifth wall is connected to the third wall and the fourth wall, the third wall extends from the second wall, and the first to fifth walls can be formed integrally.

[0086] In one embodiment of the present invention, the angle between an arbitrary line perpendicular to the first direction and the second wall may be 5° or less.

[0087] In one embodiment of the present invention, the microstructure of the molded part may be composed of martensite with an area fraction of 98% or more.

[0088] Another aspect of the present invention provides a battery pack module including a battery case formed to surround a battery pack, a base positioned at a lower portion of the battery case and connected to the battery case to form a space in which the battery pack is positioned, and a hot press-molded part positioned across the interior of the battery case and connected to the battery case and the base.

[0089] According to one embodiment of the present invention, a component with high space utilization can be manufactured when manufacturing a module such as a battery pack.

[0090] In one embodiment of the present invention, a plurality of hot press-formed parts may be arranged at regular intervals within the battery case.

[0091] Although not necessarily essential, the component according to the third aspect of the invention can be combined with the advantageous features of the other aspects described below to achieve further improved performance.

[0092] A fourth aspect of the present invention provides a press-molded part having a hat shape including a top plate portion, a vertical wall portion continuous with the top plate portion, and a boundary portion continuous with the vertical wall portion, the hat shape including a plurality of deformable portions having a preset height, and a flat plate portion arranged between the plurality of deformable portions, connecting two adjacent boundary portions, the flat plate portion having a preset length.

[0093] In one embodiment of the present invention, the relationship between the preset length and the preset height can be determined based on the number of the deformation portions.

[0094] In one embodiment of the present invention, the deformation portion is provided in three numbers, and the relationship between the preset length and the preset height is defined by the following equation (1), where w≤114.85e 0.0455h ... Formula (1), in the above formula (1), w may mean the preset length, and h may mean the preset height.

[0095] In one embodiment of the present invention, the deformation portion is provided in four or more numbers, and the relationship between the preset length and the preset height is defined by the following equation (2), where w≤46.309e 0.105h ... Formula (2), in the above formula (2), w may mean the preset length, and h may mean the preset height.

[0096] In one embodiment of the present invention, the preset length (w) may be 20 mm or more.

[0097] In one embodiment of the present invention, the press-formed part can be manufactured using a hot press forming method.

[0098] In one embodiment of the present invention, the hot press forming method may be the method described above.

[0099] Another aspect of the present invention provides a method for manufacturing a press-formed part, comprising the steps of: supplying a metal plate to a processing position; performing a first press forming on the metal plate using a first mold having a plurality of first press portions and an intermediate press portion; and, after the first press forming on the metal plate, performing a second press forming on the metal plate using the first mold and the second mold having a plurality of second press portions.

[0100] In one embodiment of the present invention, the metal plate may be a plated steel plate for hot press forming as described above.

[0101] In one embodiment of the present invention, the press forming step may use the above-described forming device.

[0102] In one embodiment of the present invention, in the step of supplying the metal plate to the processing position, the metal plate may be supplied between the first mold and the intermediate pressurizing portion, and the central region of the metal plate may be positioned facing the intermediate pressurizing portion.

[0103] In one embodiment of the present invention, in the step of supplying the metal plate to the processing position, the intermediate pressurizing portion may be located above the second mold at the processing position.

[0104] In one embodiment of the present invention, in the step of supplying the metal plate to the processing position, the intermediate pressurizing part may be positioned at a position where the height difference between the intermediate pressurizing part and the second mold is 65% or more of the height of the press-molded part.

[0105] In one embodiment of the present invention, in the step of first press forming the metal plate, the intermediate press portion is introduced into the first press portion arranged in the middle among the plurality of first press portions to press the central region of the metal plate.

[0106] In one embodiment of the present invention, in the step of performing secondary press forming on the metal plate, the second pressing portion may be introduced into a first pressing portion arranged on the outside among the plurality of first pressing portions, thereby pressing an outer region of the metal plate.

[0107] In one embodiment of the present invention, in the step of first press forming the metal plate and the step of second press forming the metal plate, the metal plate can be formed using a hot press forming method.

[0108] In one embodiment of the present invention, between the step of first press-forming the metal plate and the step of second press-forming the metal plate, the method may further include a step of press-forming the metal plate using an additional intermediate press portion arranged outside the intermediate press portion and the first mold.

[0109] According to one aspect of the present invention, by controlling the surface of the plating layer of a plated steel sheet for hot press forming, high-temperature formability can be secured during high-temperature heating for hot press forming, and paint adhesion, friction characteristics, etc. of a hot press formed part obtained by hot press forming can be secured.

[0110] According to another aspect of the present invention, a molding device capable of molding a bracket in which a flange and a curved portion are formed, a molding method, and a bracket manufactured thereby can be provided, and through such a bracket, it is possible to secure lightweight, watertight, and collision safety performance of a battery pack.

[0111] According to another aspect of the present invention, not only can a molded part be provided that has high tensile strength, small curvature, and can be manufactured at one time, making it easy to process, but also a part that has high space utilization when manufacturing modules such as battery packs can be manufactured.

[0112] According to another aspect of the present invention, an intermediate press section having a height difference is arranged between upper and lower molds, and press forming can be performed on a metal plate using three press sections. At this time, a stepwise forming process in which the central region of the metal plate is first pressed and then the outer regions are sequentially pressed can prevent deformation from being concentrated at a specific location of the metal plate during press forming. This prevents damage to the press-formed part during the manufacturing process and improves the quality of the part.

[0113] The various advantageous and beneficial advantages and effects of the present invention are not limited to the above-described contents, and will be more easily understood in the course of explaining specific embodiments of the present invention.

[0114] Figure 1 is a schematic diagram of the side frame of the battery case.

[0115] Figure 2 is a cross-sectional view taken along line A-A' of Figure 1.

[0116] Figure 3 is an exploded perspective view of a molding device according to one embodiment of the present invention.

[0117] Figure 4 is a side view of a molding device according to one embodiment of the present invention.

[0118] Figure 5 is a flow chart of a molding method according to one embodiment of the present invention.

[0119] Figure 6 is a plan view of a material fed into a molding device according to one embodiment of the present invention.

[0120] Figure 7 is a schematic perspective view showing a first molding step in a molding method according to one embodiment of the present invention.

[0121] Figure 8 is a schematic perspective view showing a second forming step in a forming method according to one embodiment of the present invention.

[0122] FIG. 9a is a perspective view showing the second molding step in a molding method according to an embodiment of the present invention from a different direction, and FIG. 9b is a front view showing the second molding step in a molding method according to an embodiment of the present invention.

[0123] Fig. 10 is a front view showing a cooling step in a molding method according to one embodiment of the present invention.

[0124] Fig. 11 is a perspective view showing a trimming step in a molding method according to one embodiment of the present invention.

[0125] Fig. 12 is a perspective view of a bracket manufactured using a molding method according to one embodiment of the present invention.

[0126] Figure 13 is a thickness reduction rate distribution diagram of a molded product manufactured using a molding method according to one embodiment of the present invention.

[0127] Figure 14 is a thickness reduction rate distribution diagram of a molded product manufactured using the molding method of Comparative Example 1-1.

[0128] Fig. 15 is a graph of the thickness reduction rate distribution in the cross section of the molded product of Figs. 13 and 14.

[0129] Figure 16 is a side view showing the forming method of Comparative Example 1-2.

[0130] Figure 17 is a perspective view of a molded product manufactured using the molding method of Comparative Example 1-2.

[0131] Fig. 18 is a perspective view of a molded part according to one embodiment of the present invention.

[0132] Fig. 19 is a front view of a molded part according to one embodiment of the present invention.

[0133] FIGS. 20a, 20b, 21a, and 21b are drawings showing an interpretation according to an embodiment of the present invention and a comparative example. Referring to Table 1, FIG. 20a shows invention example 2-1, FIG. 20b shows comparative example 2-1, FIG. 21a shows invention example 2-3, and FIG. 21b shows comparative example 2-3.

[0134] FIG. 22 is a perspective view of a battery pack module according to one embodiment of the present invention.

[0135] FIG. 23 is a drawing showing a cross-section of a portion of a battery pack module according to one embodiment of the present invention to show space utilization when a battery pack is positioned, where (a) is a case where the radius of curvature is small and (b) is a case where the radius of curvature is larger than that of (a).

[0136] Fig. 24 is a perspective view illustrating a press-formed part according to one embodiment of the present invention.

[0137] Fig. 25 is a perspective view illustrating a press-formed part according to another embodiment of the present invention.

[0138] Fig. 26 (a) is a graph showing the relationship between a preset length and a preset height of a press-molded part according to one embodiment of the present invention, and Fig. 26 (b) is a graph showing the relationship between a preset length and a preset height of a press-molded part according to another embodiment of the present invention.

[0139] Fig. 27 (a) is an example showing a strain applied to a press-formed part manufactured using a conventional manufacturing method, and Fig. 27 (b) is an example showing a strain applied to a press-formed part manufactured using a manufacturing method according to embodiments of the present invention.

[0140] Figure 28 is a flowchart showing a method for manufacturing a press-molded part according to one embodiment of the present invention.

[0141] Figure 29 schematically illustrates the first step of manufacturing the press-formed part of Figure 24.

[0142] Figure 30 schematically illustrates the second step of manufacturing the press-formed part of Figure 24.

[0143] Figure 31 schematically illustrates the third step of manufacturing the press-formed part of Figure 24.

[0144] Figure 32 schematically illustrates the fourth step of manufacturing the press-formed part of Figure 24.

[0145] Figure 33 schematically illustrates the first step of manufacturing the press-formed part of Figure 25.

[0146] Figure 34 schematically illustrates the second step of manufacturing the press-formed part of Figure 25.

[0147] Figure 35 schematically illustrates the third step of manufacturing the press-formed part of Figure 25.

[0148] Figure 36 schematically illustrates the fourth step of manufacturing the press-formed part of Figure 25.

[0149] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the invention. As used herein, the singular forms also include the plural forms, unless the context clearly dictates otherwise.

[0150] The term "comprising" as used in the specification means specifying a particular characteristic, region, integer, step, operation, element and / or component, but does not exclude the presence or addition of other particular characteristics, regions, integers, steps, operations, elements, components and / or groups.

[0151] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0152] In addition, in the present invention, the term "steel plate" refers to something in a coil or sheet state before being processed into a specific shape, and the term "material" refers to something processed into a non-plate shape through a forming process. In addition, the term "plating layer" in the present invention refers to a layer of metal, alloy, or intermetallic compound formed in contact with the base steel plate.

[0153] It should be noted that, unless otherwise specified, the content of each element in the present invention is based on weight. Furthermore, unless otherwise specified, the ratio of crystals or structures is based on area, and unless otherwise specified, the content of gas is based on volume.

[0154] Hereinafter, the present invention will be described in detail.

[0155] The inventors of the present invention have found that, in providing a plated steel sheet having an aluminum-based plated layer as a plated steel sheet for hot press forming, when controlling the surface properties of the plated layer, unlike generally controlling the roughness of the surface, specifically controlling Rt, which represents the maximum roughness of the surface of the plated layer, and the number of peaks per unit length (RPc, peak / cm) is effective in improving the high-temperature formability of the plated steel sheet for hot forming.

[0156] First, the hot press forming galvanized steel sheet according to the first aspect of the present invention may include a base steel sheet; and an aluminum-based galvanized layer on one or both sides of the base steel sheet.

[0157] According to one embodiment of the present invention, in order to improve formability during high-temperature heating for hot forming of a plated steel sheet for hot press forming, a relatively rough surface of the plated layer was secured. A larger maximum roughness (Rt) value of the plated layer surface means a rougher surface, and here, the maximum roughness (Rt) of the plated layer surface means the distance between a peak and a valley.

[0158] To this end, in one embodiment of the present invention, the Rt value of the plating layer may be 4.0 to 25.0 μm. If the Rt value of the plating layer is less than 4.0 μm, the area of ​​friction between the plating layer and the mold during hot forming of the plating steel sheet becomes larger, resulting in poor high-temperature formability. On the other hand, if the Rt value of the plating layer exceeds 25.0 μm, not only may the plating layer at the peak become incompletely alloyed during high-temperature heating for hot forming, but also the plating layer may be easily destroyed by friction with the mold during hot forming, causing sticking to the mold.

[0159] In addition, in one embodiment of the present invention, the peak number per unit length (RPc) value of the plating layer may be 30 to 90 peak / cm. If the RPc value is less than 30 peak / cm, there is a concern that plating adhesion may be reduced. On the other hand, if the RPc value exceeds 90 peak / cm, the contact area with the mold during hot forming increases, which increases the high-temperature friction coefficient, and thus there is a problem that cracks may occur during the hot forming process or the plating layer may be excessively peeled off.

[0160] Meanwhile, the inventors of the present invention have conducted in-depth research on the conditions for improving the high-temperature formability of a plated steel sheet for hot press forming, and as a result, have discovered that the desired result can be achieved by controlling the relationship between the coating layer adhesion amount and the Rt value of the plated layer surface. That is, by forming a plated layer with a certain thickness from an appropriate adhesion amount, corrosion resistance can be secured, while the frictional properties of the plated layer can be improved to enhance the formability during the high-temperature forming process. In addition, in order to secure the surface appearance of the final product, i.e., the hot-formed part, the inventors have newly identified the relationship between the coating layer adhesion amount and the maximum roughness (Rt) of the plated layer surface.

[0161] In one embodiment of the present invention, the relationship between the amount of plating layer adhesion and the Rt value of the surface of the plating layer is defined as the following relational expression 1, and the surface of the plating layer according to one embodiment of the present invention can satisfy relational expression 1. At this time, the amount of plating layer adhesion is based on one side.

[0162] [Relationship 1]

[0163] 27.0 ≤ (ⓒ / 3)+(Rt / 2) ≤ 38.0

[0164] (The unit of relational expression 1 is ㎛, and ⓒ represents the amount of plating adhesion.)

[0165] If the value of the above relational expression 1 is less than 27.0, it may be that the plating adhesion amount is high but the Rt value is low. In this case, the contact area between the steel sheet and the mold during hot forming increases, which may lead to poor hot formability due to a high coefficient of friction at high temperatures. In addition, it may be that the Rt value is high but the plating adhesion amount is low. In this case, there is a problem that the corrosion resistance of the hot-formed part is poor due to the plating layer becoming too thin.

[0166] If the value of the above relational expression 1 exceeds 38.0, it may be that the plating adhesion amount is appropriate but the Rt value is excessively high. In this case, not only is there a possibility that the plating layer at the peak may be incompletely alloyed during high-temperature heating for hot forming, but the plating layer may also be easily destroyed by friction with the mold during hot forming, causing it to arrive at the mold. In addition, it may be that the Rt value is low but the plating adhesion amount is excessively high. In this case, when the unalloyed Al plating layer is heated at high temperatures for hot forming, problems such as the plating layer being peeled off from the steel sheet may occur.

[0167] When hot forming is performed to obtain a hot-formed member using a plated steel sheet for hot press forming according to an embodiment of the present invention having the above-described characteristics, the contact area between the steel sheet and the mold can be reduced, thereby improving formability during the high-temperature forming process.

[0168] The aforementioned characteristics, i.e., the characteristics of the plating layer, were explained based on the plating layer formed on one side (single side) of the base steel sheet. Meanwhile, if the plating layer is formed on both sides of the base steel sheet, both sides of the plating layer may have the characteristics of the plating layer described above. This can also be applied equally to the plating layer of the hot press-formed part described below.

[0169] The steel sheet according to one embodiment of the present invention is a steel sheet for hot press forming, and any steel sheet used for hot press forming is possible, and there is no particular limitation on its composition.

[0170] However, as a non-limiting example, the above steel sheet may contain, in wt%, carbon (C): 0.02 to 0.60%, silicon (Si): 0.001 to 2.000%, aluminum (Al): 0.001 to 1.000%, manganese (Mn): 0.1 to 4.0%, phosphorus (P): 0.050% or less, sulfur (S): 0.0200% or less, nitrogen (N): 0.0200% or less, titanium (Ti): 0 to 1.0000%, niobium (Nb): 0 to 1.0000%, vanadium (V): 0 to 1.0000%, boron (B): 0 to 0.0100%, chromium (Cr): 0 to 1.00%, molybdenum (Mo): 0 to 1.00%, tungsten (W): 0 to 1.00%, Copper (Cu): 0~1.0%, Nickel (Ni): 0~1.0%, Antimony (Sb): 0~1.00%, Tin (Sn): 0~1.00%, Calcium (Ca): 0~0.10%, Magnesium (Mg): 0~0.10%, Cobalt (Co): 0~1.00%, Arsenic (As): 0~1.00%, Zirconium (Zr): 0~1.00%, Bismuth (Bi): 0~1.00%, Rare Earth Elements (REM): 0~0.3%, the remainder may contain Fe and other unavoidable impurities.

[0171] Among the alloy compositions described above, C, Mn, etc. can be added to secure the strength of the steel, Si is effective in reducing segregation of Mn, etc. in the base steel plate as well as having a deoxidation effect, and Al has a deoxidation effect. P, S, N, etc. may be elements that are inevitably introduced during the steel manufacturing process, but it is to be noted that the present invention is not limited thereto. In addition, it will be apparent to those skilled in the art that Ti, B, Cu, Mo, Cr, Ni, V, Ca, Nb, Sn, W, Sb, Mg, Co, As, Zr, Bi, REM, etc. may be additionally included in addition to the aforementioned composition, taking into account the target properties of the final product, etc.

[0172] Hereinafter, the alloy composition of the steel plate according to one embodiment of the present invention will be described in more detail.

[0173] Carbon (C): 0.02~0.60%

[0174] Carbon (C) is an essential element for increasing the strength of hot-formed parts, and can be included in an appropriate amount. In one embodiment of the present invention, if the C content is less than 0.02%, the target level of strength cannot be secured. On the other hand, if the content exceeds 0.60%, when producing cold-rolled materials, the strength of the hot-rolled materials obtained before cold rolling is too high, so there is a concern that the rollability of such hot-rolled materials may be greatly inferior during cold rolling, and there is a problem that the spot weldability may be greatly reduced. Therefore, in one embodiment of the present invention, C may be included in an amount of 0.02 to 0.60%. According to another embodiment of the present invention, C may be included in an amount of 0.55% or less, and in yet another embodiment, C may be included in an amount of 0.50% or less.

[0175] Silicon (Si): 0.001~2.000%

[0176] Silicon (Si) can be added as a deoxidizer in the steelmaking process and has the effect of suppressing the formation of carbides in hot-formed parts. In one embodiment of the present invention, Si may be included in an amount of 0.001% or more to achieve the aforementioned effect. However, if the content exceeds 2.000%, there is a concern that plating properties may be deteriorated due to excessive formation of Si oxide during plating of the base steel sheet. Therefore, in one embodiment of the present invention, Si may be included in an amount of 0.001 to 2.000%. According to another embodiment, the Si may be 0.010% or more, and according to yet another embodiment, the Si may be 1.500% or less.

[0177] Aluminum (Al): 0.001~1.000%

[0178] Aluminum (Al), similar to the Si, can be added as a deoxidizer in the steelmaking process, and has the effect of suppressing the formation of carbides in hot-formed parts. In one embodiment of the present invention, Al may be included in an amount of 0.001% or more to achieve the aforementioned effect. However, if the content exceeds 1.000%, there is a concern that plating properties may be poor due to excessive formation of Al oxide during plating of the base steel sheet. In addition, in order to suppress excessive temperature increase during high-temperature heat treatment for hot forming, the Al content may be 1.000% or less. Therefore, in one embodiment of the present invention, Al may be included in an amount of 0.001 to 1.000%. According to another embodiment, the Al may be 0.005% or more, and according to yet another embodiment, the Al may be 0.900% or less.

[0179] Manganese (Mn): 0.1~4.0%

[0180] Manganese (Mn) can be added not only to strengthen the solid solution but also to lower the critical cooling rate for securing a martensite phase during the manufacture of hot-formed parts. In one embodiment of the present invention, Mn may be included in an amount of 0.1% or more to sufficiently obtain the aforementioned effects. However, if the content exceeds 4.0%, there is a concern that the strength of the hot-rolled product may increase excessively, thereby lowering the cold-rollability during subsequent cold rolling, and there is also a problem that the spot weldability may be deteriorated. Therefore, in one embodiment of the present invention, Mn may be included in an amount of 0.1 to 4.0%. According to another embodiment of the present invention, the Mn may be 3.5% or less, and according to yet another embodiment, the Mn may be 3.0% or less.

[0181] Phosphorus (P): 0.050% or less

[0182] Phosphorus (P) is an element that is inevitably added during the steel manufacturing process, and it is advantageous to control its content as low as possible. In one embodiment of the present invention, if the P content is 0.050% or less, there is no problem in securing the intended physical properties, and therefore, the upper limit may be limited to 0.050%. According to another embodiment of the present invention, the P may be included at 0.040% or less, or 0.030% or less. On the other hand, since there is a concern that excessively lowering the P content in steel may significantly increase the manufacturing cost, taking this into consideration, the P content may be limited to 0.001% or more.

[0183] Sulfur (S): 0.0200% or less

[0184] Sulfur (S) is an element that is inevitably added during the steel manufacturing process, and if its content is excessive, it may impair the bendability, impact properties, weldability, etc. of the hot-formed part. Therefore, in one embodiment of the present invention, the S content may be limited to 0.0200% or less. However, since there is a concern that the manufacturing cost may increase significantly if the S content in the steel is excessively reduced, it may be limited to 0.0001% or more in consideration of this.

[0185] Nitrogen (N): 0.0200% or less

[0186] Nitrogen (N) is an element that is inevitably added during the steel manufacturing process. If its content is excessive, the sensitivity to cracking during continuous slab casting increases, and the impact properties of hot-formed parts may be inferior. Therefore, in one embodiment of the present invention, the N content may be limited to 0.0200% or less. However, since there is a concern that the manufacturing cost may increase significantly if the S content in the steel is excessively reduced, it may be limited to 0.0001% or more in consideration of this.

[0187] Titanium (Ti): 0~1.0000%, niobium (Nb): 0~1.0000%, and vanadium (V): 0~1.0000%

[0188] Titanium (Ti), niobium (Nb), and vanadium (V) combine with N in steel to form nitrides, thereby suppressing the formation of nitrides (BN) by boron, thereby improving the hardenability of the steel. In addition, by forming fine precipitates, it is effective in improving hydrogen embrittlement resistance by refining crystal grains. In one embodiment of the present invention, when the contents of Ti, Nb, and V each exceed 1.0000%, the above-described effects are saturated, which may rather cause an increase in manufacturing costs. In one embodiment of the present invention, the Ti, Nb, and V do not necessarily need to be added. However, in order to obtain the above-described effects, these elements may be included in an amount of 0.0001% or more when added.

[0189] Boron (B): 0~0.0100%

[0190] Boron (B) can improve the hardenability of steel even with a small amount of addition, and is effective in suppressing embrittlement of hot press-formed parts caused by grain boundary segregation of P and / or S by segregating at the old austenite grain boundaries. In one embodiment of the present invention, when the B content exceeds 0.0100%, the effect of B addition becomes saturated, and there is a concern that embrittlement may occur during the hot rolling process. Therefore, in one embodiment of the present invention, B may be included in an amount of 0.0100% or less. According to another embodiment of the present invention, B may be included in an amount of 0.0080% or less, or 0.0050% or less. In one embodiment of the present invention, B does not necessarily need to be added, but when B is added to obtain the above-described effect, it may be included in an amount of 0.0001% or more.

[0191] Chromium (Cr): 0~1.00%, molybdenum (Mo): 0~1.00%, and tungsten (W): 0~1.00%

[0192] Chromium (Cr), molybdenum (Mo), and tungsten (W) can be optionally added to enhance the hardenability of steel, improve strength through precipitation strengthening, and refine grain size. In one embodiment of the present invention, if the content of each element exceeds 1.00%, the effect becomes saturated, which leads to an increase in manufacturing costs.

[0193] Copper (Cu): 0~1.0% and nickel (Ni): 0~1.0%

[0194] Copper (Cu) can be added to enhance strength by forming fine precipitates in steel. Adding Cu alone can cause hot embrittlement, so nickel (Ni) can be added as needed to prevent this. In one embodiment of the present invention, if the contents of Cu and Ni each exceed 1.0%, there is a problem of significantly increasing manufacturing costs.

[0195] Antimony (Sb): 0~1.00% and tin (Sn): 0~1.00%

[0196] Antimony (Sb) and tin (Sn) play a role in suppressing the formation of oxides that may be formed on the surface grains in hot-rolled steel to which Si and / or Al are added. That is, Sb and Sn may be selectively added to suppress dent defects caused by oxides formed on the surface grain boundaries of hot-rolled steel during annealing of cold-rolled steel. In one embodiment of the present invention, if the contents of Sb and Sn each exceed 1.00%, not only will the manufacturing cost increase significantly, but also edge cracks of the coil may be induced during subsequent hot rolling by being dissolved in the grain boundaries in the slab state. Therefore, according to one embodiment of the present invention, the addition of Sb and Sn may be limited to 1.00% or less.

[0197] Calcium (Ca): 0~0.10%, Magnesium (Mg): 0~0.10%, Cobalt (Co): 0~1.00%, Arsenic (As): 0~1.00%, Zirconium (Zr): 0~1.00%, and Bismuth (Bi): 0~1.00%

[0198] In one embodiment of the present invention, the aforementioned elements may be additionally included in consideration of the target properties of the final product, etc., and when Ca and Mg are added, if the content exceeds 0.10% each, and when Co, As, Zr and Bi are added, if the content exceeds 1.00% each, the manufacturing cost increases significantly, so the content of each element may be limited.

[0199] Rare earth elements (REM): 0~0.3%

[0200] Rare earth elements (REM) control the Fe activity within the steel, and thus can be selectively added to control the thickness of the Fe scale formed on the surface of the steel sheet during hot forming. In one embodiment of the present invention, if the content of REM exceeds 0.3%, the ability to control the Fe activity may be lost, resulting in poor surface quality. Therefore, according to one embodiment of the present invention, the addition of REM can be limited to 0.3% or less.

[0201] The present invention aims to provide a plated steel sheet for hot press forming, which may include a plated layer on one or both sides of the aforementioned base steel sheet, and in this case, the plated layer may be an aluminum-based plated layer.

[0202] In one embodiment of the present invention, the aluminum-based plating layer formed on at least one surface of the base steel sheet may be a plating layer containing aluminum (Al) as a main element. As an example, the aluminum-based plating layer may include, in weight %, silicon (Si): 5.0 to 11.0%, iron (Fe): 10.0% or less, the remainder aluminum (Al), and unavoidable impurities. Such an aluminum-based plating layer may be formed by immersing the base steel sheet in an aluminum-based molten plating bath, as will be described in detail later, and it is well known that the composition of the aluminum-based plating layer is determined according to the composition of the aluminum-based molten plating bath.

[0203] Silicon (Si) within the aluminum plating layer not only lowers the melting point of the plating bath, but also prevents excessive alloying during high-temperature heating for hot forming. Accordingly, the Si content may be 5.0% or more. However, if the content exceeds 11.0%, there is a risk that the melting point of the plating bath will rapidly increase, and in this case, there is a problem that the amount of ash generated from the plating bath will rapidly increase.

[0204] The above iron (Fe) may exist as an impurity in the plating bath at approximately 4.0% or less. In addition, as Fe present in the base steel sheet during the plating process is eluted into the plating layer, it is an element included in the aluminum-based plating layer. Accordingly, the aluminum-based plating layer may contain 10.0% or less of Fe. If the Fe content in the aluminum-based plating layer exceeds 10.0%, there is a problem in that an Al-Fe alloy phase is excessively formed, increasing the possibility of the plating layer being peeled off.

[0205] According to one example of the present invention, the aluminum-based plating layer may further include, in addition to the above-described components, general elements included in the plating layer. Examples of such elements include one or two or more selected from Mg, Mn, Cr, Cu, Mo, Ni, Sb, Sn, Ti, Ca, and Sr.

[0206] Hereinafter, a method for manufacturing a plated steel sheet for hot press forming according to another aspect of the present invention will be described in detail. However, the method for manufacturing the plated steel sheet described below is only one example, and it is not necessary for the plated steel sheet of the present invention to be manufactured by this manufacturing method. It should be noted that any manufacturing method that satisfies the claims of the present invention can be used to implement each embodiment of the present invention without any problem.

[0207] According to one embodiment of the present invention, a plated steel sheet for hot press forming can be obtained by a process including the steps of preparing a base steel sheet; forming an aluminum-based plated layer on one or both sides of the base steel sheet to obtain a plated steel sheet; and performing a temper rolling process on the plated steel sheet.

[0208] In one embodiment of the present invention, the base steel sheet for obtaining the plated steel sheet for hot press forming may be the base steel sheet mentioned above, and its composition is not particularly limited, and it is to be stated that it is replaced with the above-mentioned content.

[0209] According to one embodiment of the present invention, a plating layer can be formed on one or both sides of a base steel sheet by loading the base steel sheet into a hot-dip galvanizing facility and then performing a hot-dip galvanizing process. As an example, when forming an aluminum-based plating layer as the plating layer, the hot-dip galvanizing process can be a hot-dip aluminum plating method in which the base steel sheet is immersed in a hot-dip aluminum plating bath to perform plating. At this time, the temperature of the hot-dip aluminum plating bath can be set to a temperature range for typical aluminum plating, and as a non-limiting example, it can be performed in a temperature range of 620 to 680°C.

[0210] In one embodiment of the present invention, the molten aluminum plating bath is a plating bath containing aluminum (Al) as a main component. As an example, the plating bath may contain 5.0 to 11.0 wt% of silicon (Si). In this way, by adding Si, effects such as improving the fluidity of the molten metal and suppressing the diffusion of Al into the base steel sheet during plating can be obtained.

[0211] As another example, in addition to the above Si, it may contain iron (Fe) in an amount of 4.0% or less, and in addition, it may further contain one or more kinds selected from among Mg, Mn, Cr, Cu, Mo, Ni, Sb, Sn, Ti, Ca, and Sr.

[0212] In one embodiment of the present invention, the plating amount during molten aluminum plating is 60 to 100 g / m on one side. 2 It can be. The above plating amount is 60g / m 2 If it is less than 100g / m, there is a risk of corrosion resistance decreasing, while if the plating amount is less than 100g / m, 2 If it exceeds , the weldability deteriorates, and there is a concern that the phenomenon of unalloyed Al sticking to the roll in the heating furnace during high-temperature heating for hot forming may frequently occur.

[0213] In addition, in one embodiment of the present invention, after performing the aluminum plating, a step of alloying heat treatment may be further performed. The step of performing the alloying heat treatment is not particularly limited, but may be performed by online heating in which the plated steel sheet (molten aluminum-plated steel sheet) obtained by the molten aluminum plating is heated while moving. When performing the alloying heat treatment by the above-described online heating, as an example, the heating temperature range may be 670 to 900°C, and the holding time may be 1 to 20 seconds. A plated steel sheet further subjected to the alloying treatment in this manner may be referred to as an alloyed molten aluminum-plated steel sheet.

[0214] In one embodiment of the present invention, a temper rolling treatment can be performed on a plated steel sheet having an aluminum-based plating layer formed thereon.

[0215] In one embodiment of the present invention, the temper rolling treatment of the coated steel sheet can be performed with a pressing force of 100 to 500 tons using a roll having a surface of Ra: 2.0 to 8.0 ㎛ and RPc: 46 to 120 peak / cm. That is, the condition of the roll surface and the pressing force during the temper rolling treatment of the coated steel sheet are conditions that can control the surface state of the aluminum-based coated steel sheet according to one embodiment of the present invention, and the Rt and RPc of the coated steel sheet can be affected by not only the Ra and RPc of the roll surface during the temper rolling, but also the pressing force applied by the roll.

[0216] In other words, in order to satisfy the above-described relational expression 1 while ensuring that the Rt value and the RPc value have sufficient values ​​on the surface of the plating layer of the plated steel sheet for hot press forming according to one embodiment of the present invention, the Ra value of the roll surface during the temper rolling can be limited to a range of 2.0 to 8.0 ㎛ and the RPc value can be limited to a range of 46 to 120 peak / cm. In addition, when temper rolling is performed using a roll having such a surface, rolling can be performed with a pressing force of 100 to 500 tons.

[0217] Hereinafter, a hot press-formed member and a manufacturing method thereof according to another aspect of the present invention will be described.

[0218] In one embodiment of the present invention, a hot press-formed member can be obtained by hot-forming a steel plate for hot press forming, and the steel plate for hot press forming at this time can be according to one embodiment of the present invention.

[0219] A steel sheet for hot press forming according to one embodiment of the present invention comprises a base steel sheet and an aluminum-based plating layer on at least one surface of the base steel sheet, wherein the aluminum-based plating layer has controlled Rt and RPc of its surface. A hot press forming member obtained from such a steel sheet for hot press forming can also have Rt and RPc of the plating layer surface controlled within a specific range.

[0220] In one embodiment of the present invention, the surface of the plating layer of the hot press-formed part may have a maximum roughness (Rt) of 6.0 to 26.0 μm. In addition, the surface of the plating layer of the hot press-formed part according to one embodiment of the present invention may have a peak count per unit length (RPc) of 60 to 130 peak / cm. A hot press-formed part having a plating layer with a controlled surface in this manner may have excellent paint adhesion and wear characteristics.

[0221] If the Rt value of the plating layer surface of the hot press-formed member according to one embodiment of the present invention is less than 6.0 µm or the RPc value is less than 60 peak / cm, it may be difficult to expect sufficient plating adhesion. On the other hand, if the Rt value of the plating layer surface of the hot press-formed member exceeds 26.0 µm or the RPc value exceeds 130 peak / cm, it means that the Rt and RPc values ​​of the plating layer surface of the steel sheet for hot press forming are excessively high. In this case, there is a problem that the plating layer is easily destroyed by friction with the mold during the hot forming process, causing mold sticking due to adhesive wear.

[0222] Meanwhile, the inventors of the present invention have conducted in-depth research on conditions that can improve the paint adhesion and frictional properties of hot press-formed parts. As a result, they have discovered that the desired result can be achieved by controlling the relationship between the thickness of the plating layer of the hot press-formed part and the Rt value of the plating layer surface. In particular, the inventors of the present invention have discovered that the thickness of the plating layer of the hot press-formed part and the roughness of the plating layer surface can affect the plating adhesion of the hot press-formed part obtained through high-temperature forming, as well as the securing of physical properties such as the surface appearance. Accordingly, the relationship between the thickness and the maximum roughness (Rt) of the plating layer of the hot press-formed part has been newly clarified. This will be described in detail in Arang.

[0223] According to one embodiment of the present invention, the surface of the plating layer of the hot press-formed member can satisfy the following relational expression 2.

[0224] [Relationship 2]

[0225] 40.0 ≤ T + (Rt / 2) ≤ 57.0

[0226] (The unit of equation 2 is ㎛, and T represents the thickness of the plating layer.)

[0227] If the value of the above relational expression 2 is less than 40.0, the plating adhesion of the hot press-formed part may be poor. On the other hand, if the value exceeds 57.0, there is a problem in that the plating layer is destroyed by friction with the mold during the hot forming process, causing mold sticking due to adhesive wear.

[0228] In one embodiment of the present invention, the thickness (T) of the plating layer of the hot press-formed part represented by T in relational expression 2 may be in the range of 30.0 to 50.0 μm. At this time, the thickness range is based on one side. If the thickness of the plating layer of the hot press-formed part is less than 30.0 μm, the corrosion resistance may be poor. In addition, in order to satisfy relational expression 2, the Rt value must be excessively large, which causes the plating layer to be destroyed by friction with the mold during the hot forming process, which causes mold sticking due to adhesive wear. On the other hand, if the thickness of the plating layer exceeds 50.0 μm, although it is advantageous for improving corrosion resistance, it is difficult to completely alloy the plating layer within a given heat treatment time, which lowers productivity. In addition, there is a problem that Al sticking to the roll easily occurs in the heating furnace.

[0229] In this way, a hot press-formed member having controlled surface properties according to one embodiment of the present invention has excellent frictional properties, and as one example, the hot press-formed member may have a friction coefficient of 0.50 or less.

[0230] In one embodiment of the present invention, the aluminum-based plating layer of the hot press-formed member may be a plating layer formed of an Al-Fe alloy in which the sum of the contents of Al and Fe is 89% or more (including 100%) by alloying during a high-temperature heating process for hot press forming.

[0231] In one embodiment of the present invention, the base steel plate of the hot press-formed member may have a hard structure by performing forming after high-temperature heat treatment. As one example, the base steel plate may have a microstructure comprising a combination of martensite and bainite phases with an area fraction of 90% or more, and may also include pearlite, ferrite, and the like as other structures.

[0232] Meanwhile, a method for manufacturing a hot press-formed member according to one embodiment of the present invention is not particularly limited, and can be manufactured through a process of heating a steel plate for hot press forming to a temperature higher than the austenitizing temperature, maintaining the temperature, and then rapidly cooling and forming the steel plate at the same time, as is widely known in the art.

[0233] However, as one example of the present invention, after obtaining a blank using a plated steel sheet for hot press forming according to one embodiment of the present invention, a step of heating the blank to a temperature range of 860 to 970°C and then maintaining it for 3 to 15 minutes may be performed. After hot press forming the blank heated and maintained in this manner, a step of cooling it at a cooling rate higher than the critical cooling rate may be performed, thereby manufacturing an intended hot press formed part. As a non-limiting example, the cooling may be performed at a cooling rate of 30°C / s or higher.

[0234] Hereinafter, a molding device according to a second aspect of the present invention and a molding method using the same will be described.

[0235] According to one embodiment of the present invention, there is provided a device and method for forming a bracket having a curved portion and a flange at the same time using a high-strength steel material, and a bracket for a battery case formed thereby, thereby forming a bracket for a battery case that could not be formed using high-strength steel in the past.

[0236] In one embodiment of the present invention, the high-strength steel material may be the hot press-formed galvanized steel sheet described above and may have the alloy composition described above. In addition, the material may be manufactured using the manufacturing methods described above.

[0237] FIGS. 3 and 4 illustrate a molding apparatus according to one embodiment of the present invention. Specifically, FIG. 3 illustrates an exploded perspective view of the molding apparatus according to one embodiment of the present invention, and FIG. 4 illustrates a side view of the molding apparatus according to one embodiment of the present invention. In this embodiment, the molding apparatus is illustrated with a focus on the exterior of the mold.

[0238] As shown in FIG. 3, a molding device according to one embodiment of the present invention includes a pad (A-200); a die (A-300) disposed outside the first direction (2) of the pad (A-200); and a punch (A-100) disposed below the pad (A-200) and including a body in which first to fifth punch forming portions (A-120, A-130, A-140, A-150, A-160) are formed. Although not shown in FIGS. 3 and 4, the molding device according to one embodiment of the present invention is a hot press forming device, and cooling channels (A-170, A-370; see FIG. 10) through which cooling water flows are disposed on the inside of the punch (A-100) and the die (A-300), so that the material can be hardened through heat treatment during or after molding.

[0239] The pad (A-200) and the die (A-300) are connected to the upper part of the press, and the punch (A-100) is connected to the lower part of the press, so that the material is formed while the pad (A-200) and the die (A-300) move in the third direction (4) that is the up-and-down direction toward the punch (A-100). Although not shown, the pad (A-200) and the die (A-300) are configured to be able to move independently or to move relative to each other in the up-and-down direction. For example, an elastic member may be attached to the upper part of the pad (A-200), so that the pad (A-200) and the die (A-300) move together, and after the forming of the pad (A-200) is completed, a structure may be applied in which only the die (A-300) moves downward with respect to the pad (A-200) by the elastic member.

[0240] The punch (A-100) is formed with a structure that forms two brackets simultaneously. Accordingly, it includes two forming sections corresponding to the curved portions of the brackets. Specifically, the punch (A-100) includes, when viewed from the first direction (2), a first straight punch forming portion (A-110), a second curved punch forming portion (A-120) having a curvature radius (Rp) of the forming portion along a second direction (3) perpendicular to the first direction (2) on a horizontal plane, a third straight punch forming portion (A-130), a fourth curved forming portion (A-140) having a curvature radius (Rp) of the forming portion, and a fifth straight punch forming portion (A-150), and a support portion (A-160) for supporting the material before forming is arranged on the outside of the first forming portion and the fifth forming portion (A-150).

[0241] The first and fifth punch forming parts (A-110, A-150) have a structure that is inclined toward the third punch forming part (A-130) as a whole, and the third punch forming part (A-130) has a structure that is parallel to a horizontal plane at the center, and the second and fourth punch forming parts (A-120, A-140) have a structure that curves and connects the first and fifth punch forming parts (A-110, A-150) and the third punch forming part (A-130).

[0242] The first and second punch forming parts (A-110, A-120) and the fourth and fifth punch forming parts (A-140, A-150) have a symmetrical structure centered on the third punch forming part (A-130), and thus, one bracket is formed centered on the second punch forming part (A-120), and the other bracket is formed centered on the fourth punch forming part (A-140).

[0243] The first punch forming portion (A-110) includes a first extension surface forming portion (A-111) extending along the third direction (4) to form a flange (A-21, A-23; see FIG. 2) of a bracket (A-20; see FIG. 1) on both sides of the first direction (2), a first body forming portion (A-113) formed to form a body (A-23; see FIG. 2) of the bracket (A-20), and a first curved surface forming portion (A-112) having a bending radius of curvature (r) between the first extension surface forming portion (A-111) and the first body forming portion (A-113).

[0244] The second and third punch forming portions (A-120) and the third punch forming portions (A-130) also form the flanges (A-21, A-22) of the bracket (A-20) on both sides of the first direction (2), the second and third extension surface forming portions (A-121, A-131) extending along the third direction (4), and forming the main body (A-23) of the bracket (A-20), and the second and third body forming portions (A-123, A-133) arranged below the pad (A-200) and the second and third curved surfaces having the bending radius of curvature (r) between the second extension surface forming portion (A-121) and the second body forming portion (A-113) and between the third extension surface forming portion (A-131) and the third body forming portion (A-133) It includes a molding part (A-122, A-132). At this time, the third main body molding part (A-133) and the support part (A-160) can be parallel to the horizontal plane.

[0245] Since the fourth and fifth punch forming parts (A-140, A-150) have a structure symmetrical to the first and second punch forming parts (A-110, A-120), the fourth and fifth punch forming parts (A-140, A-150) also include the fourth and fifth extension surface forming parts (A-141, A-151), the fourth and fifth curved surface forming parts (A-142, A-152), and the fourth and fifth body forming parts (A-143).

[0246] Meanwhile, the pad (A-200) includes first to fifth pressing surfaces (A-210, A-220, A-230, A-240, A-250) having shapes corresponding to the first to fifth body forming portions (A-113, A-123, A-133, A-143) of the punch (A-100). The pad (A-200) presses the material toward the top of the punch (A-100) to primarily form the material to have an overall curved portion. The pad (A-200) may have a length from a length corresponding to the third body forming portion (A-133) in the first direction (2) to the third extension surface forming portion (A-131).

[0247] The die (A-300) is arranged on both sides of the first direction of the pad (A-200) and has a structure that forms flanges (A-21, A-22). In this embodiment, the die (A-300) is arranged on both sides to form the flanges (A-21, A-22) formed on both sides of the bracket (A-20), but is not limited thereto and may be arranged on only one side. Since the shapes of the two sides of the die (A-300) are symmetrical with respect to the pad (A-200), the description will be centered on one side of the die (A-300).

[0248] When viewed from the first direction (2), the die (A-300) includes a first die forming portion (A-310) having a straight shape, a second die forming portion (A-320) having a curved shape having a die curvature radius (Rd), a third die forming portion (A-330) having a straight shape, a fourth die forming portion (A-340) having a curved shape having the die curvature radius (Rd), and a fifth die forming portion (A-310) having a straight shape, corresponding to first to fifth forming portions (A-110, A-120, A-130, A-140, A-150) of the punch (A-100). The first to fifth die forming portions (A-310, A-320, A-330, A-340, A-350) are connected via a vertical plane (A-360).

[0249] Similar to the punch (A-100) above, the first and second die forming sections (A-310, A-320) and the fourth and fifth die forming sections (A-340, A-350) in the die (A-300) have a structure that is symmetrical with respect to the third die forming section (A-330).

[0250] The first die forming portion (A-310) is adjacent to the punch (A-100) and includes a first die curved forming portion (A-311) formed into a curved surface at a position relatively close to the punch (A-100) in the first direction and a first flat forming portion (A-312) at a position relatively far from the punch (A-100).

[0251] Similarly, the second to fifth die forming sections (A-320, A-330, A-340, A-350) include second to fifth die curved forming sections (A-321, A-331, A-341, A-351) and second to fifth flat forming sections (A-322, A-332, A-342, A-352). The curved surfaces of the first to fifth die curved forming sections (A-311, A-321, A-331, A-341, A-351) increase in height as they get closer to the punch (A-100).

[0252] In this embodiment, the radius of curvature (Rd) in the second and fourth die forming portions (A-320, A-340) refers to the radius of curvature at the upper portion (A-321a, A-341a) closest to the punch (A-100) in the second and fourth curved forming portions (A-321, A-341) when viewed in the first direction (2).

[0253] As shown in Fig. 4, in this embodiment, the die (A-300) is configured so that when forming a flange, the first and fifth die forming sections (A-310, A-350) come into contact with the material first, the third die forming section (A-330) comes into contact with the material next, and the second and fourth die forming sections (A-320, A-340) come into contact with the material last, and by forming sequentially in this manner, the material between the second and fourth die forming sections (A-320, A-340) and the second and fourth punch forming sections (A-120, A-140) is secured so that stretching / contraction occurs, thereby preventing wrinkles or tears from occurring during the forming process.

[0254] Specifically, when the third body forming part (A-133) and the upper part (A-331a) of the third die forming part (A-330) are positioned (a) on the same plane, when viewed in the first direction (2), the first body forming part (A-113) is positioned (c) above the upper part (A-311a) of the first die forming part (A-310), and the second body forming part (A-123) is positioned (b) below the upper part (A-321a) of the second die forming part (A-320). The relationship between the symmetrical fourth and fifth die forming parts (A-340, A-350) and the fourth and fifth body forming parts (A-143, A-153) is also the same.

[0255] That is, when the third die forming section (A-330) starts flange forming the material, the first die forming section (A-310) is already performing flange forming, and the second die forming section (A-320), which is a curved section, is not yet performing forming.

[0256] In this embodiment, the length (lp) of the third body forming part (A-133) is longer than the length (ld) of the third die forming part (A-330), and the forming part curvature radius (Rp) of the second body forming part (A-123) is configured to be smaller than the die curvature radius (Rd) of the second die forming part (A-320), so that the above-described relationship can be achieved.

[0257] Since the die curvature radius (Rd) is formed to be larger than the die curvature radius (Rp) of the above-described forming part, the center of the die curvature radius (Rd) can be located at the center of the second direction (3) of the third die forming part (A-330). Accordingly, the centers of the die curvature radii (Rd) of the second die forming part (A-320) and the fourth die forming part (A-340) can be located at the same position, but are not limited thereto.

[0258] At this time, when viewed from the first direction, the angle (θ) at which the extensions of the imaginary tangents of both ends intersect in the fourth punch forming section (A-143) may be 90° or more, and specifically, may be between 95 and 135°, and the same is true for the second punch forming section (A-123).

[0259] Meanwhile, a forming device according to one embodiment of the present invention achieves a structure that is difficult to achieve through press forming in a conventional high-strength steel of 1200 MPa or more through hot press forming and the above-described structure, and the forming portion curvature radius (Rp) and the bending curvature radius (r) can satisfy 25 mm ≤ Rp (mm) + r (mm) ≤ 30 mm.

[0260] The bracket produced by the forming device can be used for a battery case as mentioned above. However, if the radius of curvature in the battery case is large, dead space will be generated, so the bending radius of curvature (r) that is practically permissible for forming a flange in the battery case is 10 mm or less. On the other hand, if the radius of curvature in the battery case is less than 3 mm, forming is difficult even with a hot press forming steel of 1200 MPa or more. Even if it is 3 mm, whether forming is possible or not is determined depending on the radius of curvature (Rp) of the forming part. This will be explained again when explaining the bracket for the battery case.

[0261] FIGS. 5 to 11 illustrate a molding method according to an embodiment of the present invention. FIG. 5 illustrates a flowchart of a molding method according to an embodiment of the present invention. FIG. 6 illustrates a plan view of a material fed into a molding device according to an embodiment of the present invention. FIG. 7 illustrates a schematic perspective view showing a first molding step in a molding method according to an embodiment of the present invention. FIGS. 8, 9a, and 9b illustrate a schematic perspective view, another perspective view, and a front view showing a second molding step in a molding method according to an embodiment of the present invention. FIG. 10 illustrates a front view showing a cooling step in a molding method according to an embodiment of the present invention. FIG. 11 illustrates a perspective view showing a trimming step in a molding method according to an embodiment of the present invention.

[0262] A molding method according to another aspect of the present invention can be performed by the molding device described above, and will therefore be described with reference to FIG. 3.

[0263] A forming method according to one embodiment of the present invention comprises: a material placing step (S110) of placing a heated material (A-400) on a punch (A-100) having a forming portion and having a length longer in a first direction (2) than the punch (A-100); a first forming step (S120) of forming the material (A-400) into the shape of a main body forming portion (A-113, A-123, A-133, A-143) of the punch (A-100) through a pad (A-200) positioned above the punch (A-100); a second forming step (S130) of forming the material (A-400) to follow the shape of the forming portion of the punch (A-100) through a die (A-300) positioned outside the pad (A-200) in the first direction (2); The above material includes a cooling step (S140) in which the material is cooled to have a martensite structure by at least one of the punch and the die, and a trimming step (S150) in which the cooled molded product is cut into a bracket shape.

[0264] The material settling step (S110) is a step of feeding the material into a forming device and settling it on a punch (A-100). At this time, the material is a steel plate, and the material is settling on the punch (A-100) in an austenitic state, i.e., in a state heated to a temperature higher than AC3 of the material, so that a structural change can occur during or after forming. The material may be hot press forming steel, for example, 22MnB5.

[0265] In one embodiment of the present invention, the material may be the hot press forming plated steel sheet described above, and may have the alloy composition described above.

[0266] In addition, in order to form two brackets at a time in the present invention, the material (A-400) includes notches (A-410) formed on both sides toward the center of the material in the second direction (3). The notches (A-410) cause deformation to be concentrated during forming, thereby preventing cracks from occurring in areas other than the notches (A-410).

[0267] As shown in Fig. 7, the first forming step (S120) is a step in which the material (A-400) is formed into a curve through a pad (A-200) after the material (A-400) is settled. The material (A-400) is formed by pressing the pad (A-200) onto the punch (A-100).

[0268] As shown in FIGS. 8 to 9a and 9b, the secondary forming step (S130) is a step of forming a flange on a curved material through a die (A-300), which is a step of deforming the material by applying pressure to the die (A-300) on a portion of the material (A-400) that is not in contact with the pad (A-200) that is formed primarily by the pad (A-200). At this time, as described in FIG. 4, in the secondary forming step (S130), the die (A-300) forms the edge portion, the center portion, and the middle portion between the center and the edge portion of the material in that order in the second direction (3), so that the curved portion of the primarily formed material (A-400), i.e., the second and fourth punch forming portions (A-120, A-140), can be formed last, thereby forming a flange on the material (A-400). At this time, the shape of the forming part of the punch (A-100) and die (A-300) has been described through Figs. 3 and 4.

[0269] The cooling step (S140) is a step of cooling the material (A-400) during or after forming, and cools the material (A-400) having an austenite structure by circulating a cooling fluid through a cooling channel (A-170, A-370) formed in at least one of the punch and the die, thereby transforming the austenite structure into a martensite structure, thereby making the material (A-400) a high-strength steel having a tensile strength of 1200 MPa or more. In this embodiment, the cooling channels (A-170, A-370) are formed in both the punch (A-100) and the die (A-300). If the austenite structure can be transformed into a martensite structure, the cooling channels (A-170, A-370) may be provided in only one of them, and if necessary, the cooling channels (A-170, A-370) may also be provided in the pad (A-200).

[0270] After the cooling step (S140) is completed, a trimming step (S150) is performed to cut the formed material (A-400) along the cutting line (A-420) so that only the portions corresponding to the two brackets remain. The two brackets are cut around the second and fourth punch forming portions (A-120, A-140) of the punch (A-100).

[0271] A forming method according to one embodiment of the present invention enables forming a bracket having a curved portion and a flange from high-strength steel. Furthermore, by applying a hot press forming method, springback occurring during forming in high-strength steel can be prevented, and forming errors, such as wrinkles or thinning, caused by forming a flange on the curved portion can be prevented.

[0272] FIG. 12 shows a perspective view of a bracket manufactured using a molding method according to one embodiment of the present invention.

[0273] The bracket (A-20) of Fig. 12 has a main body (A-23) and flanges (A-21, A-22), and is curved overall with a curvature radius (Rp) of the molded portion. At this time, the flanges (A-21, A-22) are connected to the main body (A-23) by a curved surface (A-24) that is curved with a curvature radius (r). The surface of the main body (A-23), the flanges (A-21, A-22) of the bracket (A-20), and the curved surface (A-24) therebetween that is formed with the curvature radius (Rp) of the molded portion can be called a molded surface.

[0274] FIG. 13 shows a thickness reduction rate distribution diagram of a molded product manufactured by a molding method of one embodiment of the present invention (embodiment 1-1), FIG. 14 shows a thickness reduction rate distribution diagram of comparative example 1-1 manufactured by another molding method, and FIG. 15 shows a thickness reduction rate distribution graph in a cross section of the molded products of FIGS. 13 and 14.

[0275] The thickness reduction rate distribution diagram is a diagram showing how the thickness of the material (A-400, see Fig. 6) changes after molding. The thickness reduction rate is obtained by subtracting the thickness of the bracket (A-20) at the corresponding location from the initial thickness (tini) of the material (A-400) and dividing the result by the initial thickness (tini). A positive number means that the thickness has decreased, and a negative number means that the thickness has increased.

[0276] The example of Fig. 13 was manufactured using the molding device of Fig. 3, and a material heated to have a martensite structure with 22MnB5 steel was supplied and the cooling rate was adjusted, and the tensile strength of the bracket was 1500 MPa. At this time, the thickness of the material was 1.2 t, the bending radius of curvature (r) was 5 mm, and the forming portion curvature radius of curvature (Rp) was 22 mm.

[0277] As shown in FIGS. 13 and 15, since the thickness of the main body (A-23) in the bracket (A-20) is not different from the initial thickness (tini), the average thickness (tav) of the main body (A-23) of the bracket (A-20) can be regarded as the initial thickness (tini) of the material (A-400), and the value obtained by subtracting the thickness of each location from the average thickness (tav) of the main body (A-23) and dividing it by the average thickness (tav) can be regarded as the thickness reduction rate.

[0278] Comparative Example 1-1 is a product formed by supplying 1500 MPa mart steel as a material through the same forming device.

[0279] As shown in Fig. 15, when manufacturing a bracket using the molding device and molding method according to one embodiment (embodiment 1-1) of the present invention, the maximum thickness reduction rate, that is, the thickness reduction rate of the portion having the minimum thickness (tmin), does not exceed 0.2. However, in the case of Comparative Example 1-1, it can be confirmed that the thickness reduction rate of the portion with the thinnest thickness exceeds 0.2. When the thickness reduction rate exceeds 0.2, a height difference may occur at the flanges (A-21, A-22), which may deteriorate the sealing performance when manufacturing the battery case.

[0280] In addition, as shown in Fig. 15, even if the bracket is curved and elongation is dominant, shrinkage occurs in certain parts, and if buckling occurs due to this shrinkage, damage to the material may occur. In the case of the bracket according to the forming method according to one embodiment of the present invention, a thickness reduction rate of -0.3 or less did not occur even at the maximum thickness (tmax) position on the curved surface, and thus, it was confirmed that stable forming was achieved even in the curved portion.

[0281] However, in the case of Comparative Example 1-1, a thickness reduction rate of -0.8 occurs at the maximum thickness (tmax) position, and buckling occurs in that area. Such buckling leads to cracks, which not only harm the structural performance of the battery case, but also may allow water to flow into that area, so a bracket like Comparative Example 1-1 cannot be applied to a battery case. In order to maintain sealing properties, it is advantageous to maintain a thickness reduction rate of -0.4 or higher even in the curved area.

[0282] Meanwhile, the sum of the curvature radius (Rp) of the molded part and the bending curvature radius (r) had to be 25 mm or more to enable molding. However, when the curvature radius (r) of the molded part was less than 3 mm, it was difficult to mold a bracket applicable to a battery case even with the molding device and method according to an embodiment of the present invention. In addition, even if flange molding was possible when the curvature radius (r) of the molded part was 3 mm and the bending curvature radius (r) was less than 22 mm, molding was not properly performed at the flange of the curved part. Meanwhile, when the curvature radius (r) of the molded part and the curvature radius (Rp) of the molded part increased, the molding itself was not difficult, but there was a problem that the curvature radius increased in the battery case, resulting in a dead space, which was impractical. Therefore, it is preferable that the sum of the curvature radius (Rp) of the molded part and the bending curvature radius (r) be 30 mm or less for a bracket applicable to a battery case.

[0283] In addition, in the bracket (A-20), the angle (θ) at which the extension lines of the virtual contacts intersect at both ends of the molding surface may be between 95 and 135°. If the angle (θ) is less than 95°, the molding is not properly performed even if the conditions of the molding portion curvature radius (Rp) and the bending curvature radius (r) are satisfied. If the angle (θ) exceeds 135°, the battery case must be configured with an angle exceeding an octagon, resulting in dead space where the battery cells, which are roughly rectangular in shape, are not filled, making it impractical.

[0284] Meanwhile, Fig. 16 shows a side view showing the molding method of Comparative Example 1-2, and Fig. 17 shows a perspective view of a molded product manufactured using the molding method of Comparative Example 1-2.

[0285] The molding method of Fig. 16 is formed in the same order as the molding method of the present invention, but in the second molding step (S130), the flange molding is not performed in the order of edge-center-curved part in the second direction (3), but in the order of center-curved part-edge. In Comparative Example 1-2, the die (A-300) is formed so that the center has the lowest upper position (A-301a), and the molding is performed sequentially as it goes outward.

[0286] Even if the hot press forming process is applied in the same way in this case, as shown in Fig. 17, a folding area (B) is created, and a bracket that cannot be used as a battery case is produced.

[0287] Although the present invention has been described above with reference to embodiments thereof, it is to be understood that the present invention is not limited thereto and may be implemented in various modified forms.

[0288] Hereinafter, a hot press-formed part according to the third aspect of the present invention will be described.

[0289] FIG. 18 illustrates a perspective view of a molded part according to one embodiment of the present invention, and FIG. 19 illustrates a front view of a molded part according to one embodiment of the present invention.

[0290] A hot press-formed part according to one embodiment of the present invention includes a first wall (B-110) extending in a first direction (Y direction) and a second wall (B-120) extending in a direction intersecting the first wall (B-110), a curvature (B-160) is formed between the first wall (B-110) and the second wall (B-120), an angle between an arbitrary line perpendicular to the first direction (a line parallel to the Z direction) and the second wall (B-120) is 0° or more and 5° or less, and the first wall (B-110), the second wall (B-120) and the curvature (B-160) are formed integrally.

[0291] A hot press-formed part according to one embodiment of the present invention includes a first wall (B-110), a second wall (B-120), and a curved portion (B-160) positioned between the first wall (B-110) and the second wall (B-120). The first wall (B-110), the curved portion (B-160), and the second wall (B-120) are integrally formed in that order.

[0292] A hot press-formed part has the characteristic of being formed as a single body, including a first wall (B-110) formed parallel to a first direction, a curved portion (B-160) curved from the first wall (B-110), and a second wall (B-120) connected to one end of the curved portion (B-160).

[0293] Assuming an arbitrary line perpendicular to the first direction, the second wall (B-120) may have an angle of 0° or more and 5° or less with the arbitrary line.

[0294] In response to the demand for vehicle weight reduction and improved safety, many parts using high-strength steel are being produced. However, due to the poor bendability of high-strength steel, it is difficult to produce parts with a small curvature radius.

[0295] Hot press forming is a processing method that heats a blank, press-forms the heated blank into the desired shape, and then cools the blank with the mold closed to produce a high-strength molded part. This hot press forming method, which uses a hot press forming method that forms at high temperatures, has excellent characteristics such as an elongation of over 50% at the high temperature during forming, allowing for the formation of parts with a small curvature radius without cracks, making it possible to secure the shapes of molded parts that cannot be achieved with cold ultra-high strength.

[0296] One embodiment of the present invention relates to a molded part (B-10) formed as an integral part including a first wall (B-110), a curved portion (B-160), and a second wall (B-120) through a hot press forming method, wherein the second wall (B-120) has an angle of 0° or more and 5° or less with respect to the arbitrary line, which is smaller than a conventional angle. Accordingly, the first wall (B-110) and the second wall (B-120) have a shape close to a right angle, and thus can be efficiently used in the space surrounded by the first wall (B-110) and the second wall (B-120).

[0297] According to one embodiment of the present invention, the first wall (B-110), the second wall (B-120) and the curved portion (B-160) can be formed integrally by processing a plate material.

[0298] The first wall (B-110), the curved portion (B-160), and the second wall (B-120) can be integrally formed using a blank formed by joining a single plate or multiple plates in the thickness direction by a hot press forming method. Since the blank is integrally formed by hot press forming, processing is convenient, and processing problems or breakage due to stress concentration at joints such as welds can be prevented, while a molded part (B-10) having a relatively high tensile strength can be manufactured.

[0299] In one embodiment of the present invention, the plate may be the hot press forming plated steel plate described above and may have the alloy composition described above.

[0300] According to one embodiment of the present invention, the radius of curvature (r) of the curved portion (B-160) may be greater than or equal to 0.5 mm, and the limit bending (r / t), which is the ratio of the thickness (t) of the plate material and the radius of curvature (r), may be formed to be less than 2.5.

[0301] The ratio (r / t) of the thickness (t) of the sheet metal before processing to the radius of curvature (r) is generally determined by the limit bending value of the raw material. The limit bending can be viewed as a numerical value expressing the maximum radius of curvature without lag in relation to the thickness of the material. Since the thickness (t) of the sheet metal is usually set before processing, if the radius of curvature is reduced to a value lower than the ratio (r / t) that can be formed in the sheet metal, cracks will occur on the molded part (B-10).

[0302] According to one embodiment of the present invention, the ratio (r / t) of the thickness (t) of the plate and the radius of curvature (r) may be less than 2.5. In comparison, the limit bending of existing ultra-high strength materials with a tensile strength of 1500 MPa is known to be 2.5 or more. For example, this means that the minimum radius of curvature of a part that can be formed with an ultra-high strength of 1500 MPa from a material having a thickness of 1.0 mm is 2.5 mm or more. However, according to the present invention, even when forming with ultra-high strength, the ratio (r / t) may have a value less than 2.5, so that a product with a ratio (r / t) of less than 2.5 can be formed even from an ultra-high strength material with a tensile strength of 1500 MPa. Therefore, a molded part according to one embodiment of the present invention may be a part with excellent formability and high space utilization. According to one embodiment of the present invention, the third wall (B-130) and the fourth wall (B-140) are parallel to the first direction, and the fifth wall (B-150) is connected to the third wall (B-130) and the fourth wall (B-140), and the third wall (B-130) extends from the second wall (B-120), and the first wall (B-110) to the fifth wall (B-150) can be formed integrally.

[0303] According to the hot press forming process, a hat-shaped shape with multiple walls can be formed at once, resulting in excellent formability.

[0304] For example, a third wall (B-130) and a fourth wall (B-140) may be formed parallel to the first direction, and the first wall (B-110) and the fourth wall (B-140) may have the same height in a direction perpendicular to the first direction, but this is not limited thereto. In addition, the third wall (B-130) may have a different height. The fifth wall may be positioned between the third wall (B-130) and the fourth wall (B-140), the second wall (B-120) and the third wall (B-130) may be connected by a first connecting portion (B-170), the third wall (B-130) and the fifth wall (b-150) may be connected by a second connecting portion (B-180), and the fifth wall (B-150) and the fourth wall (B-140) may be connected by a third connecting portion (B-190). Accordingly, the first to fifth walls (B-150), the curved portion (B-160), and the first connecting portion (B-170) to the third connecting portion (B-190) may be integrally formed by processing a plate material.

[0305] Here, the first connecting portion (B-170) to the third connecting portion (B-190) can be formed into a shape having a radius of curvature like the curved portion (B-160), and at this time, the radius of curvature may have all the characteristics of the curved portion (B-160) of the first wall (B-110) and the second wall (B-120). However, it is not limited to this shape.

[0306] According to one embodiment of the present invention, the tensile strength of the molded part may be 1300 to 2100 MPa.

[0307] The tensile strength referred to as ultra-high strength is generally around 1500 MPa. According to the present invention, a molded part having a tensile strength of around 1300 to 2100 MPa, which can be considered high strength or ultra-high strength, can be manufactured. This is because the formability is improved by hot press forming, and thus the molded part according to one embodiment of the present invention can be manufactured as an integral part and have an ultra-high tensile strength while forming a part with a relatively small radius of curvature.

[0308] In addition, by utilizing the excellent formability at high temperatures for hot press forming at the strengths of 1800 MPa and 2000 MPa, parts with a small radius of curvature as described above can be formed. Therefore, according to the present invention, molded parts with a small radius of curvature having a tensile strength of 1700 MPa to 1900 MPa, or even 1900 MPa to 2100 MPa, can also be produced.

[0309] In addition, the microstructure forming the molded part (B-10) may be composed of martensite with an area fraction of 98% or more. The molded part (B-10) according to the present invention may be composed of martensite, a hard phase with high strength, occupying most of the area fraction, thereby forming a tensile strength of the ultra-high strength level as described above.

[0310] For example, more than 98% of the area fraction may be formed as martensite, and other phases such as trace amounts of ferrite or bainite may be included.

[0311] According to one embodiment of the present invention, when a third wall (B-130) is further included that is parallel to the first direction and connected to the second wall (B-120), and a length in a direction perpendicular to the first direction from the first wall (B-110) to the third wall (B-130) is defined as a wall height (hw), and an angle between an arbitrary line perpendicular to the first direction and the second wall (B-120) is defined as a wall angle (θw), the following relational expression 3 can be satisfied.

[0312] [Relationship 3]

[0313] hw ≤ 13.4 * θw + 182.4

[0314] Here, the unit of hw is mm, the unit of θw is degree, and the left and right sides are nondimensionalized and calculated.

[0315] A molded part processed by hot press forming that satisfies the above relational expression 3 can be manufactured with excellent quality without defects such as cracks.

[0316] Referring to Table 1 below, it can be seen that formability is excellent when the above formula is satisfied.

[0317] θw(°)hw(mm)Calculated value of the right sideRelationship 3 Satisfaction Formability Invention Example 2-10 180 182.4 Satisfactory Good Invention Example 2-21 190 195.8 Satisfactory Good Invention Example 2-33 220 222.6 Satisfactory Good Invention Example 2-45 240 249.4 Satisfactory Good Comparison Example 2-10 190 182.4 Unsatisfactory Poor Comparison Example 2-21 200 195.8 Unsatisfactory Poor Comparison Example 2-33 230 222.6 Unsatisfactory Poor Comparison Example 2-45 260 249.4 Unsatisfactory Poor

[0318] Comparative Examples 2-1 to 2-4 were formed identically to Invention Examples 2-1 to 2-4, except for the wall heights indicated above. However, the comparative examples had problems in that the forming results revealed defects in formability, such as cracks.

[0319] Fig. 20a is a drawing interpreted in the same manner as the conditions of Invention Example 2-1, and Fig. 20b is a drawing interpreted in the same manner as the conditions of Comparative Example 2-1. Comparing Figs. 20a and 20b, it can be seen that in Comparative Example 2-1, a crack occurs in the upper part of the second wall (B-120) or the fifth wall (B-150), indicated in red, and some parts are interpreted as parts at risk of crack occurrence, indicated in yellow.

[0320] Fig. 21a is a drawing interpreted in the same manner as the conditions of Invention Example 2-3, and Fig. 21b is a drawing interpreted in the conditions of Comparative Example 2-3. Comparing Figs. 21a and 21b, it can be seen that in Comparative Example 2-3, a crack, indicated in red, occurs in the lower part of the second wall (B-120) or the fifth wall (B-150), and some parts are interpreted as parts at risk of crack occurrence in yellow. In comparison, in Invention Example 2-3, there are some parts at risk of crack occurrence in yellow, but no cracks occur.

[0321] Hereinafter, another aspect of the present invention, a battery pack module, will be described.

[0322] The battery pack module below includes the molded part described above, and the description of the molded part is cited above.

[0323] FIG. 22 is a drawing illustrating a battery pack module according to one embodiment of the present invention, and FIG. 23 is a drawing expressing a cross-section of a portion of the battery pack module to show space utilization when the battery pack is positioned, where (a) illustrates a case where the radius of curvature of a hot press-formed part is small, and (b) illustrates a case where the radius of curvature is larger than that of (a).

[0324] A battery pack module (B-1) according to one embodiment of the present invention includes a battery case (B-20) formed to surround a battery pack, a base (B-30) positioned at a lower portion of the battery case (B-20) and connected to the battery case (B-20) to form a space in which the battery pack is positioned, and a hot press-molded part (B-10) positioned across the interior of the battery case (B-20) and connected to the battery case (B-20) and the base (B-30).

[0325] The battery case (B-20) is formed to surround the side of the battery pack, and the base (B-30) is formed of a general plate material or has curves or grooves as needed, and is formed to place the battery pack.

[0326] For example, a reinforcing member (B-40) may be further included to be bonded to the outer surface of the battery case (B-20) to prevent collision.

[0327] For example, a hot press-formed part (B-10) can serve as a cross member to reinforce rigidity against impact caused by collision of the battery frame and can be positioned inside the battery case (B-20).

[0328] For example, the hot press-formed parts (B-10) may be arranged in multiple numbers at regular intervals within the battery case (B-20).

[0329] The battery pack is positioned in the space formed between the base (B-30), the battery case (B-20), and the cross member, and the battery pack module (B-1) is intended to stably position the battery in the vehicle body, including the battery pack.

[0330] The radius of curvature within the battery pack is formed smaller than before, and high tensile strength molded parts are positioned, thereby increasing the rigidity of the battery pack module (B-1) itself, thereby preventing fires caused by damage to the battery due to impact.

[0331] In addition, since a plurality of cross members are generally provided within the battery case (B-20), the size of the battery pack can be increased according to the benefit of increased space utilization, and therefore, if the battery pack module (B-1) has the same volume, it provides the effect of increasing the battery capacity.

[0332] As an example of a case where it is used as a cross member, when the radius of curvature r2 of the lower end of the hot press-formed part (B-10b) of embodiment 2-2 of FIG. 23 (b) is formed to be larger than the radius of curvature r1 of the lower end of the hot press-formed part (B-10a) of embodiment 2-1 of FIG. 23 (a), the gap, which is the remaining space after the battery pack (b) is positioned, can be compared. It can be seen that the gap g2 of FIG. 23 (b) is formed to be larger than the gap g1 of FIG. 23 (a), and as the radius of curvature (r) increases, the space that cannot be used for mounting the battery pack (b) becomes larger.

[0333] And as the radius of curvature (r) decreases, the space utilization increases, which can be seen to have greater utility when multiple cross members are mounted within the same battery pack module (B-1).

[0334] Hereinafter, a hot press-formed part according to the fourth aspect of the present invention will be described.

[0335] Fig. 24 is a perspective view illustrating a press-molded part according to one embodiment of the present invention. Fig. 25 is a perspective view illustrating a press-molded part according to another embodiment of the present invention. Fig. 26 (a) is a graph showing the relationship between a preset length and a preset height of a press-molded part according to one embodiment of the present invention, and Fig. 26 (b) is a graph showing the relationship between a preset length and a preset height of a press-molded part according to another embodiment of the present invention. In addition, Fig. 27 (a) is an example showing a strain applied to a press-molded part manufactured using a conventional manufacturing method, and Fig. 27 (b) is an example showing a strain applied to a press-molded part manufactured using a manufacturing method according to embodiments of the present invention.

[0336] Referring to FIGS. 24 and 25, press-formed parts (C-10, C-10') according to embodiments of the present invention can be manufactured by performing press-forming processing on a metal plate. At this time, a hot press forming method can be used to manufacture the press-formed parts (C-10, C-10').

[0337] The press-formed part (C-10, C-10') may include a flat portion (C-110) that is not press-formed and thus has a flat shape, and a deformed portion (C-120) that is a portion that is convex in one direction due to press-forming. At this time, a plurality of deformed portions (C-120) may be formed. In this case, the flat portions (C-110) may be arranged between a plurality of deformed portions (C-120).

[0338] The deformation portion (C-120) may have a convex shape protruding upward (+Z) based on the drawing. At this time, the deformation portion (C-120) may include a top plate portion (C-121), a longitudinal wall portion (C-122), and a boundary portion (C-123).

[0339] The top plate (C-121) may be the upper end of a deformation portion (C-120) extending in a first direction. Here, the first direction may be, for example, a direction parallel to the longitudinal direction (Y) of the press-formed part (C-10, C-10').

[0340] The longitudinal wall portion (C-122) may be a side wall portion of the deformation portion (C-120) extending along a second direction. Here, the second direction may be a different direction from the first direction described above. For example, the second direction may be a direction inclined at a predetermined angle with respect to the first direction. As another example, the second direction may be a direction perpendicular to the first direction and parallel to the vertical direction (Z) in the drawing. Meanwhile, the vertical direction (Z) described above may be parallel to the height direction of the deformation portion (C-120).

[0341] The longitudinal wall portion (C-122) may be continuous with the top plate portion (C-121). More specifically, the longitudinal wall portion (C-122) may be arranged so that its upper end is continuous with one side end of the top plate portion (C-121). A pair of such longitudinal wall portions (C-122) may be provided. A pair of longitudinal wall portions (C-122) may be arranged so as to be continuous with each of the two side ends of the top plate portion (C-121), thereby forming two side wall portions of the deformation portion (C-120).

[0342] The portion (hereinafter, shoulder portion) (C-121a) where the side edge of the top plate portion (C-121) and the upper end of the longitudinal wall portion (C-122) are connected may have a round shape having a first radius of curvature. In this case, the shoulder portion (C-121a) may be convexly curved toward the outside of the deformation portion (C-120).

[0343] The boundary portion (C-123) may be a boundary between a deformation portion (C-120) and a flat portion (C-110) that are continuous along the longitudinal direction (Y) of the press-molded part (C-10, C-10'). One end of the boundary portion (C-123) may be continuous with the lower end of the longitudinal wall portion (C-122), and the other end of the boundary portion (C-123) may be continuous with one end of the flat portion (C-110). At this time, the other end of the flat portion (C-110) may be continuous with a boundary portion (C-123) provided in another deformation portion (C-120). A pair of such boundary portions (C-123) may be provided, and arranged to be continuous with each of the lower ends of the pair of longitudinal wall portions (C-122).

[0344] The boundary portion (C-123) may be rounded with a second radius of curvature. The boundary portion (C-123) may be concavely curved inwardly of the deformation portion (C-120). In this case, the second radius of curvature may be the same as or similar to the first radius of curvature.

[0345] As described above, the deformation portion (C-120) may have a shape in which a boundary portion (C-123), a longitudinal wall portion (C-122), a top plate portion (C-121), a longitudinal wall portion (C-122), and a boundary portion (C-123) are sequentially connected along the longitudinal direction (Y). Accordingly, the deformation portion (C-120) may have a shape like a hat or a similar shape.

[0346] As described above, a plurality of deformation sections (C-120) may be provided. More specifically, at least three deformation sections (C-120) may be provided. In this case, a flat section (C-110) may be placed between two adjacent deformation sections (C-120) among the plurality of deformation sections (C-120). In this case, the two adjacent deformation sections (C-120) may be connected by the flat section (C-110) located at the center thereof.

[0347] Accordingly, the press-formed part (C-10, C-10') may have a form in which three or more deformed parts (C-120) and a plurality of flat parts (C-110) are arranged alternately in a row along the longitudinal direction (Y). At this time, the flat parts (C-110) may be arranged on both outer sides of the press-formed part (C-10, C-10') based on the longitudinal direction (Y), but the present invention is not limited thereto.

[0348] The deformation portion (C-120) can be formed to a preset height (h). At this time, the preset height (h) is the height of the deformation portion (C-120), and may mean the length from the lower surface of the flat portion (C-110) to the upper surface of the top plate portion (C-121).

[0349] Two adjacent deformation sections (C-120) may be spaced apart by a preset length (w) along the longitudinal direction (Y). Here, the preset length (w) may refer to the length of the flat section (C-110) measured with respect to the longitudinal direction (Y). At this time, the preset length (w) may be measured with respect to the flat section (C-110) positioned between the two adjacent deformation sections (C-120).

[0350] As illustrated in FIG. 24, a press-formed part (C-10) according to one embodiment of the present invention (hereinafter, Embodiment 3-1) may include three deformed portions (C-120). Accordingly, the press-formed part (C-10) of Embodiment 3-1 may include at least two flat portions (C-110) so as to be arranged between the three deformed portions (C-120).

[0351] As illustrated in FIG. 25, a press-formed part (C-10') according to another embodiment of the present invention (hereinafter, Embodiment 3-2) may include four or more deformed portions (C-120). Accordingly, the press-formed part (C-10) of Embodiment 3-1 may include at least three flat portions (C-110) so as to be arranged between the four or more deformed portions (C-120).

[0352] Meanwhile, although the drawing only illustrates a case where the press-formed part (C-10') has four deformation sections (C-120), the present invention is not limited thereto. Although not illustrated in the drawing, as another example, the press-formed part (C-10') may have five or more deformation sections (C-120), and in this case, the upper limit of the number of deformation sections (C-120) is not limited.

[0353] Referring to FIGS. 26 and 27, in the case of the conventional hot press forming method, the deformation portion (C-120) is first formed, and then a separate flat metal plate is bonded to the lower end of the formed deformation portion (C-120). In this case, as the number of deformation portions (C-120) to be formed increases, as exemplarily illustrated in (a) of FIG. 27, the force (deformation force) (stress) is concentrated on the vertical wall portion (C-122) to which the flat metal plates are connected and its surrounding area [A1 and B1 of FIG. 27 (a)] during the manufacturing process. As a result, there is a disadvantage in that cracks, etc. occur in the deformation portion (C-120) of the press-formed part, causing damage. To prevent this, the distance between the connected deformation parts (C-120) must be increased, but since the size of the press-formed part (C-10, C-10') being manufactured is inevitably limited, there is a problem that the number of deformation parts (C-120) that can be included in it is also limited.

[0354] Accordingly, in one embodiment of the present invention, a press-formed part (C-10, C-10') capable of preventing damage to a deformation part (C-120) due to hot press forming is provided by utilizing the relationship between the height (preset height) (h) of a deformation part (C-120) and the distance (preset length) (w) between two adjacent deformation parts (C-120). At this time, the "relationship between the preset height (h) and the preset length (w)" can be determined based on the number of deformation parts (C-120) formed in the press-formed part (C-10, C-10').

[0355] In the case of the press-formed part (C-10) according to embodiment 3-1 of the present invention, since three deformation parts (C-120) are formed, the relationship between the “preset height (h)” of the deformation parts (C-120) and the “preset length (w)” of the distance between two adjacent deformation parts (C-120) can be defined by the following equation (1).

[0356] w min ≤w≤114.85e 0.0455h ... Formula (1)

[0357] Here, w may mean the preset length of embodiment 3-1, and h may mean the preset height of embodiment 3-1. And, w min may mean the minimum value (i.e., minimum interval) of the preset length (w) of embodiment 3-1.

[0358] As shown in the graph of Fig. 26 (a) and Fig. 27 (b), when three deformation sections (C-120) included in a press-formed part (C-10) are designed so that the distance (pre-set length) (w) apart from each other satisfies the formula (1), the occurrence of damage such as cracks in the deformation section (C-120) and its surrounding area [A2 and B2 in Fig. 27 (b)] during the hot press forming process can be minimized. At this time, the manufacturing method of the press-formed part (C-10) according to embodiment 3-1 will be described in detail below.

[0359] In addition, in the case of the press-formed part (C-10) according to embodiment 3-2 of the present invention, since four or more deformation parts (C-120) are formed, the relationship between the “preset height (h)” of the deformation parts (C-120) and the “preset length (w)” of the distance between two adjacent deformation parts (C-120) can be defined by the following equation (2).

[0360] w min ≤w≤46.309e 0.105h ... Formula (2)

[0361] Here, w may mean the preset length of embodiment 3-2, and h may mean the preset height of embodiment 3-2. And, w min may mean the minimum value of the preset length of embodiment 3-2.

[0362] As shown in the graph of Fig. 26 (b) and Fig. 27 (b), when three deformation sections (C-120) included in a press-formed part (C-10) are designed so that the distance (predetermined length) (w) apart from each other satisfies the formula (1), the occurrence of damage such as cracks in the deformation section (C-120) and its surrounding area [A2 and B2 in Fig. 27 (b)] can be minimized during the hot press forming process. At this time, the manufacturing method of the press-formed part (C-10) according to embodiment 3-1 will be described in detail below.

[0363] Meanwhile, in the above-described embodiment 3-1 and embodiment 3-2, the preset length (w) may be 20 mm or more. That is, the minimum distance (w) between two adjacent deformation parts (C-120) min ) may be 20 mm. This may be the minimum gap required to secure space for arranging cooling holes (not shown) between the first pressurizing parts (C-210) provided in the molds (C-200, C-400) and / or between the second pressurizing parts (C-410) and the intermediate pressurizing parts (C-300) in the manufacturing device (C-20, C-20') of the press-molded parts (C-10, C-10') to be described later.

[0364] Fig. 28 is a flowchart illustrating a method for manufacturing a press-formed part according to one embodiment of the present invention. Fig. 29 schematically illustrates a first step for manufacturing the press-formed part of Fig. 24. Fig. 30 schematically illustrates a second step for manufacturing the press-formed part of Fig. 24. Fig. 31 schematically illustrates a third step for manufacturing the press-formed part of Fig. 24. And, Fig. 32 schematically illustrates a fourth step for manufacturing the press-formed part of Fig. 24.

[0365] Referring to FIGS. 28 to 32, a manufacturing device (C-20) for manufacturing a press-molded part (C-10) according to embodiment 3-1 may include a first mold (C-200), an intermediate pressurizing part (C-300), and a second mold (C-400). In this case, one intermediate pressurizing part (C-300) may be provided. At this time, based on the vertical direction (Z), the first mold (C-200) may be an upper mold, and the second mold (C-400) may be a lower mold.

[0366] The first mold (C-200) and the second mold (C-400) may be arranged to face each other along the pressing direction (-Z). The first mold (C-200) may be arranged above the second mold (C-400). At this time, the first mold (C-200) may be installed on an upper support (not shown) that can be elevated. Accordingly, the first mold (C-200) may be lowered toward the second mold (C-400) or elevated away from the second mold (C-400). In addition, the second mold (C-400) may be arranged on a lower support (not shown) that is fixedly installed on the floor surface of a building where the manufacturing device (C-20) is installed, for example.

[0367] The first mold (C-200) may be provided with a first pressurizing portion (C-210). The first pressurizing portion (C-210) may pressurize the upper surface of a metal plate during press forming. Here, the metal plate may be a material used to manufacture a press-formed part (C-10). Before press forming, the metal plate may have, for example, a flat upper surface and a flat lower surface. At this time, the first pressurizing portion (C-210) may be configured to have a shape and size corresponding to the "upper surface of the deformed portion (C-120) of the press-formed part (C-10)" described above.

[0368] The manufacturing device (C-20) is for manufacturing the press-molded part (C-10) of embodiment 3-1, and may be provided with three first pressurizing portions (C-210). At this time, the three first pressurizing portions (C-210) may be spaced apart from each other by a first distance. The first distance may be the same distance as the preset length (w) described above. In addition, the first mold (C-200) may be provided with a first flat portion (C-220). The first flat portion (C-220) may be arranged between two adjacent first pressurizing portions (C-210). The first flat portion (C-220) may extend parallel to the longitudinal direction (Y) between the two first pressurizing portions (C-210), thereby connecting the first pressurizing portions (C-210). As described above, since three first pressurized portions (C-210) are provided, at least two first flat portions (C-220) may be provided.

[0369] Accordingly, the first mold (C-200) may be formed such that three first pressurizing portions (C-210) are spaced apart from each other by a first distance (i.e., a preset length) (W) along the longitudinal direction (Y), and a first flat portion (C-220) is arranged between them to connect the first pressurizing portions (C-210).

[0370] The second mold (C-400) may be provided with a second pressurizing portion (C-410) and a second flat portion (C-420a). At this time, the second pressurizing portion (C-410) may be formed in a shape and size corresponding to the lower surface of the press-molded part (C-10).

[0371] Unlike the first mold (C-200), the second mold (C-400) may be provided with only two second pressurizing portions (C-410). In this case, the two second pressurizing portions (C-410) may be arranged symmetrically with the two first pressurizing portions (C-210) located on both sides among the three first pressurizing portions (C-210) along the longitudinal direction (Y). Accordingly, in the second mold (C-400), the second pressurizing portion (C-410) may not exist in the area (hereinafter, the center area) facing the first pressurizing portion (C-210) in the middle among the three first pressurizing portions (C-210).

[0372] Accordingly, the second mold (C-400) may be a single structure having a form connected by two second pressurizing portions (C-410) and a second flat portion (C-420a) disposed therebetween. At this time, the flat portion (C-420a) may be provided with a penetrating portion (C-420aa). When press forming the outer region of the metal plate (C-10A), an intermediate pressurizing portion (C-300) may be inserted into the penetrating portion (C-420aa). The penetrating portion (C-420aa) may be formed by penetrating a portion of the flat portion (C-420a) along the vertical direction (Z). This penetrating portion (C-420aa) may have a cross-sectional shape and area corresponding to the shape and size of the intermediate pressurizing portion (C-300). Additionally, a second-second flat section (C-420b) may be further provided on each side of the first pressurized section (C-210).

[0373] The intermediate pressurizing portion (C-300) may be placed between the first mold (C-200) and the second mold (C-400). As illustrated in Fig. 38, the metal plate (C-10A), which is a press-molding target, may be placed on the lower side of the first mold (C-200). In this case, the intermediate pressurizing portion (C-300) is positioned between the metal plate (C-10A) and the second mold (C-400), and may pressurize a portion of the lower surface of the metal plate (C-10A) when the first mold (C-200) is lowered. The intermediate pressurizing portion (C-300) may be, for example, a pad for pressing and bending the lower surface of the metal plate (C-10A).

[0374] The intermediate pressurizing portion (C-300) may be positioned directly above the above-described central region of the second mold (C-400). At this time, the intermediate pressurizing portion (C-300) may have the same shape as the second pressurizing portion (C-410). That is, the intermediate pressurizing portion (C-300) may have a shape and size corresponding to the lower surface of the press-molded part (C-10). During press molding, the intermediate pressurizing portion (C-300), together with the middle first pressurizing portion (C-210) among the three first pressurizing portions (C-210), may pressurize the metal plate (C-10A) upward and downward to form the deformation portion (C-120) located in the center.

[0375] The intermediate pressurizing section (C-300) may be configured to be elevable. Accordingly, the intermediate pressurizing section (C-300) can descend along the pressing direction (-Z) during press forming. In addition, the intermediate pressurizing section (C-300) can rise in the opposite direction (Z) to the pressing direction after press forming is completed. This elevation of the intermediate pressurizing section (C-300) can be realized by an elastic member (not shown) installed in the intermediate pressurizing section (C-300).

[0376] The “manufacturing method of a press-molded part (C-10) according to embodiment 3-1” using the above manufacturing device (C-20) may be as follows.

[0377] First, a metal plate (C-10A) can be supplied to a manufacturing device (C-20) (S100). Before press forming begins, as illustrated in FIG. 29, the metal plate (C-10A) can be placed at a position (hereinafter referred to as a processing position) between the first mold (C-200) and the intermediate pressurizing portion (C-300). Meanwhile, the metal plate (C-10A) can be supplied to the manufacturing device (C-20) while being heated by a separate heating device (not illustrated).

[0378] For example, when the metal plate (C-10A) is the processing position, the upper surface of the metal plate (C-10A) may be positioned so that it contacts the lower surface of the first mold (C-200) or there is only a slight gap therebetween. At this time, the second mold (C-400) may be positioned symmetrically with the first mold (C-200), with the metal plate (C-10A) and the intermediate pressurizing portion (C-300) interposed therebetween.

[0379] In addition, when the metal plate (C-10A) is placed at the processing position (i.e., before press forming begins), the intermediate pressurizing portion (C-300) may be placed on the upper side of the second mold (C-400). Accordingly, a height difference (hi) may exist between the intermediate pressurizing portion (C-300) and the second pressurizing portion (C-410). Here, the height difference (hi) may mean the distance from the upper surface of the second pressurizing portion (C-410) to the upper surface of the intermediate pressurizing portion (C-300). In this case, the height difference (hi) between the intermediate pressurizing portion (C-300) and the second pressurizing portion (C-410) may be smaller than the “preset height (h)”, which is the height of the press-formed part (C-10). At this time, the height difference (hi) may be 65% or more of the preset height (h). When the manufacturing device (C-20) is configured to have such a height difference (hi), damage such as cracks in the deformed portion (C-120) formed through press forming can be minimized.

[0380] Next, the metal plate (C-10A) can be first press-formed by the first mold (C-200) and the intermediate pressurizing member (C-300) (S200). As illustrated in Fig. 30, the first mold (C-200) can be lowered along the pressing direction (-Z) to pressurize the upper surface of the metal plate (C-10A). In this case, the first mold (C-200) can be lowered to a position where the lower surface of the metal plate (C-10A) does not come into contact with the second mold (C-400). At this time, since the intermediate pressurizing member (C-300) is positioned higher than the second pressurizing member (C-410) by the height difference (hi), only the intermediate pressurizing member (C-300) is inserted into the first pressurizing member (C-210) and can pressurize the center region of the metal plate (C-10A). Accordingly, only the central region of the metal plate (C-10A) can be pressed in the vertical direction by the central first pressing portion (C-210) among the three first pressing portions (C-210) and the intermediate pressing portion (C-300). Accordingly, only the central region of the metal plate (C-10A) can be bent, thereby forming one deformed portion (C-120).

[0381] Next, the metal plate (C-10A) can be secondarily press-formed by the first mold (C-200) and the second mold (C-400) (S300). After the first press-formed is performed in step S200, the first mold (C-200) can be further lowered along the pressing direction (-Z), as illustrated in FIG. 31. In this process, the intermediate pressurizing portion (C-300) can be lowered together with the first mold (C-200) while being inserted into the central first pressurizing portion (C-210) together with the central region of the metal plate (C-10A). Accordingly, the outer region of the metal plate (C-10A) can come into contact with the upper surfaces of the two second pressurizing portions (C-410).

[0382] Thereafter, as the first mold (C-200) continues to descend, the second pressurizing portion (C-410) is introduced into the first pressurizing portion (C-210) and can pressurize both outer regions of the metal plate (C-10A). In this process, the intermediate pressurizing portion (C-300) can be accommodated into the through portion (C-420aa) of the second mold (C-400). Both outer regions of the metal plate (C-10A) can be simultaneously pressed in the vertical direction by the two outer first pressurizing portions (C-210) and the two outer second pressurizing portions (C-410). As a result, both outer regions of the metal plate (C-10A) are bent, so that two additional deformed regions (C-120) can be formed.

[0383] Next, the first mold (C-200) and the intermediate pressurizing portion (C-300) can be returned to their original positions (S400). After the "stepwise press forming" in steps S200 and S300 as described above, as illustrated in FIG. 32, the first mold (C-200) can be raised in the opposite direction (+Z) to the pressing direction (-Z). In this process, the deformation portions (C-120) can be separated from the first pressure portions (C-210). In addition, the intermediate pressurizing portion (C-300) can be separated from the central deformation portion (C-120) and returned to its original position. As a result, a press-formed part (C-10) having three deformation portions (C-120) having a preset height (h) and spaced apart from each other by a preset length (w) can be manufactured.

[0384] Then, the press-formed part (C-10) that has been manufactured can be discharged (S500). After being discharged from the manufacturing device (C-20), the press-formed part (C-10) can be transported for the next processing or manufacturing process. Thereafter, the next metal plate (C-10A) is supplied, so that the aforementioned manufacturing method can be repeatedly performed.

[0385] Fig. 33 schematically illustrates the first step of manufacturing the press-formed part of Fig. 25. Fig. 34 schematically illustrates the second step of manufacturing the press-formed part of Fig. 25. Fig. 35 schematically illustrates the third step of manufacturing the press-formed part of Fig. 25. And Fig. 36 schematically illustrates the fourth step of manufacturing the press-formed part of Fig. 25.

[0386] Referring to FIG. 28 and FIG. 33 to FIG. 36, a press-molded part (C-10) according to embodiment 3-2 can be manufactured through the following manufacturing method. A manufacturing apparatus (C-20') for a press-molded part can include a first mold (C-200), an intermediate pressurizing part (C-300), and a second mold (C-400). At this time, at least two intermediate pressurizing parts (C-300) can be provided. In this case, most of the features of the first mold (C-200), the intermediate pressurizing part (C-300), and the second mold (C-400) are the same or similar to those of the aforementioned embodiment 3-1, and therefore, a duplicate description thereof will be omitted.

[0387] Since the press-molded part (C-10') according to embodiment 3-2 is provided with four or more deformation sections (C-120), the first mold (C-200) may be provided with four or more first pressurizing sections (C-210). For convenience of explanation, the following description will focus on a case where four first pressurizing sections (C-210) are provided and are spaced apart from each other by a preset length (w). In this case, two first pressurizing sections (C-210) may be arranged in the center area of ​​the first mold (C-200), and one first pressurizing section (C-210) may be arranged on each side of the center.

[0388] The second mold (C-400) may be provided with two second pressurizing parts (C-410). At this time, the two second pressurizing parts (C-410) may be arranged to face the two first pressurizing parts (C-210) arranged on each side of the first mold (C-200).

[0389] When four first pressurizing sections (C-210) are provided, two intermediate pressurizing sections (C-300) may be provided. In this case, the two intermediate pressurizing sections (C-300) may be arranged to face the two first pressurizing sections (C-210) arranged in the center area of ​​the first mold (C-200). As in the case described above, the intermediate pressurizing sections (C-300) are arranged between the first mold (C-200) and the second mold (C-400).

[0390] In addition, in the case of embodiment 3-2, the second flat portion (C-420a) of the second mold (C-400) may be provided with two through-hole portions (C-420aa). Accordingly, when the outer region of the metal plate (C-10A) is press-formed by the first mold (C-200) and the second mold (C-400), the two intermediate pressurizing portions (C-300) can be accommodated in the through-hole portions (C-420aa), respectively.

[0391] In the case of the "method for manufacturing a press-molded part (C-10') according to Embodiment 3-2" using the above-described manufacturing device (C-20'), steps S100, S200, S300, and S400 can be sequentially performed, similarly to the method for manufacturing the press-molded part (C-10) of Embodiment 3-1. At this time, since the specific manufacturing method performed at each step is the same or similar to that of Embodiment 3-1, the description will focus on the differences.

[0392] First, in step S100, as illustrated in FIG. 33, the metal plate (C-10') may be supplied to the aforementioned processing position. In this case, the metal plate (C-10A) may be supplied to the manufacturing device (C-20') in a heated state by a separate heating device (not illustrated). When supplied to the processing position, two intermediate pressurizing parts (C-300) may be positioned below the center region of the metal plate (C-10'). At this time, the two intermediate pressurizing parts (C-300) may be arranged at the same height. In this case, the height difference (hi) between the intermediate pressurizing parts (C-300) and the second pressurizing parts (C-410) is the same as in the case of embodiment 3-1.

[0393] Next, in step S200, as illustrated in FIG. 34, as the first mold (C-200) is lowered, the intermediate pressurizing portions (C-300) are each introduced into the two first pressurizing portions (C-210) arranged in the central region of the first mold (C-200), and the central region of the metal plate (C-10') can be pressed. By this first press forming step, two deformation portions (C-120) can be formed in the central region of the metal plate (C-10A).

[0394] Next, in step S300, as illustrated in FIG. 35, the first mold (C-200) may be lowered further, and the second pressurizing portions (C-410) may be introduced into the two first pressurizing portions (C-210) arranged in the outer region of the first mold (C-200), respectively. Accordingly, the outer region of the metal plate (C-10') may be pressed in the vertical direction by the first pressurizing portions (C-210) and the second pressurizing portions (C-410). By this second press forming step, two deformation portions (C-120) may be additionally formed in the outer region of the metal plate (C-10A).

[0395] Next, in step S400, as illustrated in FIG. 36, the first mold (C-200) can be raised in the opposite direction (+Z) to the pressing direction (-Z). Accordingly, the press-formed part (C-10') in a press-formed state can be separated from the first mold (C-200), the intermediate pressurizing part (C-300), and the second mold (C-400). In this process, the two intermediate pressurizing parts (C-300) can be raised and returned to their original positions at the processing positions described above.

[0396] Then, after the manufactured press-formed part (C-10') is discharged from the manufacturing device (C-20'), the next press-formed process can begin as a new metal plate (C-10') is supplied.

[0397] Meanwhile, when the number of deformation parts (C-120) formed in the press-molded part (C-10') increases, the number of intermediate pressurized parts (C-300) may also increase accordingly.

[0398] For example, although not shown in the drawing, if five deformation sections (C-120) are formed in a press-molded part (C-10'), the first mold (C-200) must be provided with five first pressurizing sections (C-210). Accordingly, three intermediate pressurizing sections (C-300) may be provided, and may be arranged to face the three first pressurizing sections (C-210) arranged in the center area of ​​the first mold (C-200). In this case, the three intermediate pressurizing sections (C-300) may be arranged between the first mold (C-200) and the second mold (C-400).

[0399] Among the three intermediate pressurizing parts (C-300), one intermediate pressurizing part (hereinafter, the first intermediate pressurizing part) (C-300) arranged in the middle may be arranged at the highest position. The remaining two intermediate pressurizing parts (hereinafter, the second intermediate pressurizing parts) (C-300) may be arranged between the first intermediate pressurizing part (C-300) and the second mold (C-400). At this time, the two second intermediate pressurizing parts (C-300) may be arranged at the same height. The height difference between the first intermediate pressurizing part (C-300) and the second intermediate pressurizing part (C-300) may be the same as or similar to the height difference (hi) between the aforementioned intermediate pressurizing part (C-300) and the second pressurizing part (C-410).

[0400] In this arrangement, first press forming can be performed by the first mold (C-200) and the first intermediate press portion (C-300). When the first press forming is completed or immediately before completion, the first mold (C-200) is lowered further together with the first intermediate press portion (C-300), so that second press forming can be performed by the first mold (C-200) and the two second intermediate press portions (C-300). By these two press formings, forming of the center region of the metal plate (C-10A) can be performed first. Thereafter, after the second press forming is completed or immediately before completion, the first mold (C-200) is lowered further, so that third press forming of the outer region of the metal plate (C-10A) can be performed by the first mold (C-200) and the second mold (C-400).

[0401] As another example, although not shown in the drawing, if six deformation sections (C-120) are formed in a press-molded part (C-10'), the first mold (C-200) must be provided with six first pressurizing sections (C-210). Accordingly, four intermediate pressurizing sections (C-300) may be provided, and may be arranged to face the four first pressurizing sections (C-210) arranged in the center area of ​​the first mold (C-200). In this case, the four intermediate pressurizing sections (C-300) may be arranged between the first mold (C-200) and the second mold (C-400).

[0402] Among the four intermediate pressurizing parts (C-300), the two intermediate pressurizing parts (hereinafter, first intermediate pressurizing parts) (C-300) arranged in the middle may be arranged at the highest position. The remaining two intermediate pressurizing parts (hereinafter, second intermediate pressurizing parts) (C-300) may be arranged between the first intermediate pressurizing part (C-300) and the second mold (C-400). At this time, the two first intermediate pressurizing parts (C-300) may be arranged at the same height. And, the two second intermediate pressurizing parts (C-300) may also be arranged at the same height. The height difference between the first intermediate pressurizing part (C-300) and the second intermediate pressurizing part (C-300) may be the same as or similar to the height difference (hi) between the aforementioned intermediate pressurizing part (C-300) and the second pressurizing part (C-410).

[0403] In this arrangement, first press forming can be performed by the first mold (C-200) and the two first intermediate press portions (C-300). When the first press forming is completed, or immediately before completion, the first mold (C-200) is lowered further together with the first intermediate press portions (C-300), so that second press forming can be performed by the first mold (C-200) and the two second intermediate press portions (C-300). By these two press formings, forming of the central region of the metal plate (C-10A) can be performed first. Thereafter, after the second press forming is completed or just before completion, the first mold (C-200) is lowered further, whereby the third press forming can be performed on the outer area of ​​the metal plate (C-10A) by the first mold (C-200) and the second mold (C-400).

[0404] In addition, when the number of deformation sections (C-120) formed in the press-molded part (C-10') increases to 7 or more, the number of the first pressurizing sections (C-210) and the intermediate pressurizing sections (C-300) must be further increased similarly to the above. Accordingly, the number of penetration sections (C-420aa) in the second mold (C-400) can also be increased. With the manufacturing device configured in this manner, by adding a press-molding step, press-molding can be performed first on the center region of the metal plate (C-10A), and then press-molding can be performed on the outer region of the metal plate (C-10A).

[0405] The press-formed parts (C-10, C-10') and the manufacturing method (S10) thereof according to the embodiments of the present invention as described above can perform press forming on a metal plate (C-10, C-10') by arranging an intermediate press portion (C-300) having a height difference (hi) between upper / lower molds (C-200, C-400) and using three press portions (C-210, C-300, C-410). At this time, through a step-by-step forming process of first pressing the center region of the metal plate (C-10, C-10') and then sequentially pressing the outer region, it is possible to prevent deformation force from being concentrated at a specific location of the metal plate (C-10, C-10') during press working. As a result, the press-formed parts (C-10, C-10') can be prevented from being damaged during the manufacturing process and the quality of the parts can be improved.

[0406] Although the embodiments of the present invention have been described with reference to the attached drawings, those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics thereof. Therefore, the embodiments described above should be understood to be illustrative in all respects and not restrictive.

[0407] [Explanation of symbols]

[0408] A-1: Side Frame A-10: Frame

[0409] A-20: Bracket A-21, A-22: Flange

[0410] A-23: Body A-24: Curved surface

[0411] A-100: Punch

[0412] A-110, A-120, A-130, A-140, A-150: 1st to 5th punch forming sections

[0413] A-111, A-121, A-131, A-141, A-151: First to fifth extension surface forming parts

[0414] A-112, A-122, A-132, A-142, A-152: First to fifth curved forming sections

[0415] A-113, A-123, A-133, A-143: First to fourth main body molding parts

[0416] A-200: Pad

[0417] A-300: Die

[0418] A-310, A-320, A-330, A-340, A-350: 1st to 5th die forming sections

[0419] A-311, A-321, A-331, A-341, A-351: First to fifth die curved forming sections

[0420] A-312, A-322, A-332, A-342, A-352: 1st to 5th die flat forming sections

[0421] A-360: Vertical plane

[0422] A-400: Material A-410: Notch

[0423] B-1: Battery pack module B-10: Hot press molded part

[0424] B-20: Battery Case B-30: Base

[0425] B-40: Reinforcing member B-110: First wall

[0426] B-120: Second wall B-130: Third wall

[0427] B-140: 4th wall B-150: 5th wall

[0428] B-160: Curved portion B-170: First connecting portion

[0429] B-180: Second connection B-190: Third connection

[0430] b: battery pack r: radius of curvature

[0431] t: plate thickness θw: wall angle

[0432] hw: wall height

[0433] C-10, C-10': Press-formed parts

[0434] C-10A: Metal plate

[0435] C-110: Flatbed

[0436] C-120: Transformation section

[0437] C-20, C-20': Press forming device

[0438] C-200: Mold 1

[0439] C-210: First projection

[0440] C-220: First plane section

[0441] C-300: Intermediate pressurization section

[0442] C-400: Second mold

[0443] C-410: Second protrusion

[0444] C-420: Second plane

[0445] Hereinafter, the present invention will be described in detail through examples. However, it should be noted that the following examples are intended only to illustrate the present invention through examples and are not intended to limit the scope of the invention. This is because the scope of the invention is determined by the matters set forth in the patent claims and matters reasonably inferred therefrom.

[0446] (Example)

[0447] A cold-rolled steel sheet for hot press forming having the composition shown in Table 2 below was prepared as a base steel sheet. The base steel sheet was annealed by a conventional method and then subjected to molten aluminum plating. The plating bath had a composition consisting essentially of 9.5 wt% of Si, 4.0 wt% or less of Fe, and the balance Al, and the plating bath temperature was 660°C. After plating, the plating adhesion amount was adjusted based on one side using an air knife. At this time, each plating adhesion amount was measured using the sodium hydroxide-antimony trichloride hydrochloric acid stripping gravimetric method of KS D 3544: 2002, and the values ​​are shown in Table 3 below.

[0448] Afterwards, the condition of the surface of the plating layer of each plating steel sheet was controlled by subjecting each plating steel sheet to temper rolling with the pressing force shown in Table 3 using rolls having the Ra and RPc values ​​shown in Table 3.

[0449] Next, for each of the above-mentioned temper-rolled galvanized steel sheets, the steel sheets were heated and maintained in an air atmosphere under the conditions shown in Table 4, and then press-formed and rapidly cooled to obtain hot press-formed parts. Each of the obtained hot press-formed parts had a tensile strength of 1000 MPa or more, and it was confirmed that the internal structure was substantially composed of a hard phase of martensite and bainite.

[0450] In order to confirm the surface characteristics of each of the plated steel sheets and hot press-formed parts manufactured as described above, the maximum roughness (Rt) and the number of peaks per unit length (RPc, peak / cm) were measured for each plated layer surface. At this time, the Rt and RPc values ​​were measured at five locations according to the JIS B 0301 standard, and the average value of the values ​​was calculated and presented. Among the measurement results, the results for the plated steel sheets are shown together in Table 3 below, and the results for the hot press-formed parts are also shown in Table 3. In addition, the thickness (T) of the plated layer of each hot press-formed part was measured at five locations at equal intervals at 500x magnification using an optical microscope, and then the other five locations were measured at equal intervals at the same magnification, and the average value was calculated and presented.

[0451] And, the paint adhesion, friction coefficient, adhesive wear weight increase, and alloying degree of each hot press-formed part were evaluated by the following method, and the results are shown in Table 5.

[0452] First, the paint adhesion grade was determined by applying paint to a material obtained according to the GMW14829 method, forming grid scratches at 1 mm intervals, and evaluating the tape peeling. A grade of 0 or lower was evaluated as good.

[0453] The coefficient of friction was evaluated by strip drawing at 750°C for each specimen heated and maintained according to the heating conditions shown in Table 4 below, and the coefficient of friction value (μ) was calculated according to the equation below.

[0454] μ = F D / (2F N )

[0455] Here, FD is the force pulling the specimen, FN is the force applied by the mold to the specimen during friction, and the pressure during evaluation was 5 MPa, the pulling speed was 100 mm / sec, and the pulling distance was 280 mm. In addition, SKD11 tool steel surface-treated with chromium (Cr) was used as the mold, and the hardness value of this mold was 58.2±0.4 HRC. The mold size was 20×20×9 mm. 3 The shape was a hexahedron, and the end of the surface that rubs against the specimen was rounded to 1.5 mm. To ensure the reliability of the measurement value, the test was performed three times and the average value was calculated.

[0456] The increase in contact wear weight was expressed by measuring the weight of the attachment attached to the mold after 10 repetitions in the same manner as when measuring the coefficient of friction, and calculating the difference in weight increase after the test compared to the weight before the test.

[0457] The alloying degree was determined by collecting samples from five random locations for each hot-formed member, observing the cross-section of the plating layer of each sample with an optical microscope at 1000x magnification, calculating the area of ​​the entire plating layer where no Al plating layer remained and where the area was completely alloyed, and expressing the value (average value).

[0458] Steel alloy composition (weight %)CSiMnPSAlNTiNbBCrMoOtherA0.080.701.50.0100.01500.0800.00700.0300.030.00200.200Cu0.4Ni0.2Mg0.05B0.220.101.20.0120.01000.0200.00400.04000.00300.300W0.50Ca0.05Co0.30C0.311.001.80.0110.00500.0400.01200.15000.00500.100.15Sb0.03Sn0.04As 0.05D0.420.020.80.0070.00200.1200.00100.0010.1500.800V 0.5REM 0.1Zr 0.30Bi 0.03

[0459] Surface / bottom adhesion amount of galvanized steel sheet coated with temper rolling conditional on steel grade (g / m) 2 )Ra(㎛)RPc(peak / cm)Pressure(ton)Rt(㎛)RPc(peak / cm)Relationship 1AUpper75.91.0454003.22526.9Comparative Example 1Lower73.23.42426.1AUpper74.63.01141004.57527.1Invention Example 1Lower74.44.77427.2AUpper77.23.0481004.33427.9Invention Example 2Lower75.74.63827.5BUpper70.61.0451002.93225.0Comparative Example 2Lower64.52.83022.9BUpper72.33.01141008.68528.4Invention Example 3Ha69.08.28627.1BSang71.26.01065021.37834.4Comparative example 3Ha58.115.17826.9CSang81.63.011450014.16034.3Invention example 4Ha74.714.55632.2CSang81.56.06240021.44537.9Invention example 5Ha76.220.74635.8CSang90.12.011450010.15735.1Invention example 6Ha81.29.85732.0DSang82.63.04850014.83534.9Invention example 7Ha91.414.23537.6DSang80.46.010660026.17539.9Comparative Example 4Ha76.126.77538.7

[0460] As shown in Table 3, it can be confirmed that the surface properties of the plated steel sheet obtained by satisfying the plating conditions and temper rolling conditions proposed in one embodiment of the present invention satisfy the intention of the present invention.

[0461] On the other hand, when the conditions of the temper rolling roll or the reduction ratio conditions are outside the range according to one embodiment of the present invention, the surface properties of the plating layer could not satisfy at least one of the properties.

[0462] Steel grade, galvanized surface heating condition, hot press forming, member classification, temperature (℃), holding time (min), galvanized layer thickness (㎛), Rt (㎛), Rpc (peak / cm), relational expression 2A, top 930, 534.6, 6.25, 737.7, comparative example 1, bottom 33.45, 35, 836.1A, top 930, 536. 29. 4, 10, 140.9, invention example 1, bottom 36.19, 510, 040.9A, top 930, 540. 56. 96, 544.0, invention example 2, bottom 38.47, 067, 41.9B, top 930, 535. 76, 059, 38.7, comparative example 2, bottom 32.15, 85, 835.0B, top 930, 538. 01, 11, 71, 2643.9, invention example 3Ha35.111.612840.9BSang950538.019.513147.8Comparative example 3Ha24.718.413533.9CSang930543.214.19450.3Invention example 4Ha40.514.39147.7CSang930544.819.28554.4Invention example 5Ha41.518.48650.7CSang930549.015.19256.6Invention example 6Ha46.715.09254.2DSang900546.418.06155.4Invention example 7Ha48.117.56256.9DSang950548.226.813261.6Comparative example 4ha48.026.913461.5

[0463] ClassificationPlating surfaceFriction coefficientAlloying degreePaintingAdhesionAdhesionWearWeight increase (mg)Comparative example 1Phase 0.5310022Ha10022Invention example 1Phase 0.4910004Ha10004Invention example 2Phase 0.4710002Ha10001Comparative example 2Phase 0.5410012Ha10012Invention example 3Phase 0.4710005Ha10004Comparative example 3Phase 0.4410008Ha10009Invention example 4Phase 0.4310003Ha10002Invention example 5Phase 0.4210003Ha10003Invention example 6Phase 0.4110003Ha10003Invention example 7Phase 0.4110005Ha10005Comparative example 4th phase 0.379607th phase 9708th phase

[0464] As shown in Tables 4 and 5, it can be confirmed that the hot press-formed parts obtained by hot press-forming the plated steel sheet having the surface properties intended in the present invention satisfy the surface properties proposed in one embodiment of the present invention. From this, each of the hot press-formed parts had good or excellent friction coefficients, plating adhesion, adhesive wear properties, and alloying properties.

[0465] On the other hand, when hot press forming a plated steel sheet that does not have the surface properties intended in the present invention (comparative example), at least one of the surface properties of the obtained hot press formed parts did not satisfy what is proposed in one embodiment of the present invention.

[0466] In addition, these hot press-formed parts did not satisfy one or more of the properties shown in Table 5. Comparative Examples 1 and 2 had inferior coefficients of friction and paint adhesion, and Comparative Examples 3 and 4 had inferior adhesive wear characteristics.

[0467] Although the present invention has been described above with reference to examples, the present invention is not limited to the above-described examples, and it goes without saying that modifications can be made and implemented by those skilled in the art without changing the technical idea of ​​the present invention as claimed in the claims.

Claims

1. A steel plate; and an aluminum-based plating layer is included on one or both sides of the steel plate, and the maximum roughness (Rt) of the surface of the plating layer is 4.0 to 25.0 ㎛. A hot press forming galvanized steel sheet in which the relationship between the adhesion amount of the above-mentioned galvanized layer and Rt satisfies the following relational expression 1. [Relationship 1] 27.0 ≤ (ⓒ / 3)+(Rt / 2) ≤ 38.0 (The unit of relational expression 1 is ㎛, and ⓒ represents the amount of plating adhesion.) 2. In paragraph 1, The above aluminum-based plating layer is a hot press forming plating steel sheet having a peak number per unit length (RPc) of 30 to 90 peaks / cm.

3. In paragraph 1, A hot press forming galvanized steel sheet having a composition in which the aluminum-based plating layer contains, in weight %, silicon (Si): 5.0 to 11.0%, iron (Fe): 10.0% or less, the remainder aluminum (Al), and other unavoidable impurities.

4. In paragraph 1, The above steel sheet contains, in weight %, carbon (C): 0.02 to 0.60%, silicon (Si): 0.001 to 2.000%, aluminum (Al): 0.001 to 1.000%, manganese (Mn): 0.1 to 4.0%, phosphorus (P): 0.050% or less, sulfur (S): 0.0200% or less, nitrogen (N): 0.0200% or less, titanium (Ti): 0 to 1.0000%, niobium (Nb): 0 to 1.0000%, vanadium (V): 0 to 1.0000%, boron (B): 0 to 0.0100%, chromium (Cr): 0 to 1.00%, molybdenum (Mo): 0 to 1.00%, tungsten (W): 0 to 1.00%, copper (Cu): A hot press forming galvanized steel sheet having a composition containing 0~1.0% nickel (Ni), 0~1.0% antimony (Sb), 0~1.00% tin (Sn), 0~1.00% calcium (Ca), 0~0.10% magnesium (Mg), 0~0.10% cobalt (Co), 0~1.00% arsenic (As), 0~1.00% zirconium (Zr), 0~1.00% bismuth (Bi), 0~1.00% rare earth elements (REM), 0~0.3%, the remainder iron (Fe), and other unavoidable impurities.

5. Step for preparing the steel plate; A step of forming an aluminum-based plating layer on one or both sides of the above-mentioned steel plate to obtain a plated steel plate; and It includes a step of subjecting the above-mentioned galvanized steel sheet to temper rolling treatment, The above-mentioned temper rolling treatment is a method for manufacturing a galvanized steel sheet for hot press forming, which is performed with a pressing force of 100 to 500 tons using a roll having a surface of Ra: 2.0 to 8.0 ㎛ and RPc: 46 to 120 peak / cm.

6. In paragraph 5, The step of forming the above aluminum-based plating layer to obtain a plated steel sheet is as follows: A method for manufacturing a plated steel sheet for hot press forming, which is performed by immersing the above-mentioned steel sheet in an Al-based plating bath containing, by weight %, Si: 5.0 to 11.0%, Fe: 4.0% or less, the remainder Al, and other unavoidable impurities.

7. In paragraph 5, A method for manufacturing a plated steel sheet for hot press forming, further comprising a step of performing alloying heat treatment by heating the plated steel sheet on which the aluminum-based plated layer is formed at a temperature range of 670 to 900°C.

8. In paragraph 5, The above steel sheet contains, in weight %, carbon (C): 0.02 to 0.60%, silicon (Si): 0.001 to 2.000%, aluminum (Al): 0.001 to 1.000%, manganese (Mn): 0.1 to 4.0%, phosphorus (P): 0.050% or less, sulfur (S): 0.0200% or less, nitrogen (N): 0.0200% or less, titanium (Ti): 0 to 1.0000%, niobium (Nb): 0 to 1.0000%, vanadium (V): 0 to 1.0000%, boron (B): 0 to 0.0100%, chromium (Cr): 0 to 1.00%, molybdenum (Mo): 0 to 1.00%, tungsten (W): 0 to 1.00%, copper (Cu): A method for manufacturing a galvanized steel sheet for hot press forming having a composition including 0~1.0%, nickel (Ni): 0~1.0%, antimony (Sb): 0~1.00%, tin (Sn): 0~1.00%, calcium (Ca): 0~0.10%, magnesium (Mg): 0~0.10%, cobalt (Co): 0~1.00%, arsenic (As): 0~1.00%, zirconium (Zr): 0~1.00%, bismuth (Bi): 0~1.00%, rare earth elements (REM): 0~0.3%, the remainder being iron and other unavoidable impurities.

9. Includes a steel plate and an aluminum-based plating layer having a thickness (T) of 30.0 to 50.0 ㎛ formed on the steel plate, The maximum roughness (Rt) of the surface of the above plating layer is 6.0 to 26.0 ㎛, A hot-formed member in which the relationship between the thickness of the above-mentioned plating layer and Rt satisfies the following relational expression 2. [Relationship 2] 40.0 ≤ T + (Rt / 2) ≤ 57.0 (The unit of equation 2 is ㎛, and T represents the thickness of the plating layer.) 10. In paragraph 9, The above aluminum-based plating layer is a hot-formed member having a peak number per unit length (RPc) of 60 to 130 peaks / cm.

11. In paragraph 9, A hot-formed member, wherein the aluminum-based plating layer is made of an Al-Fe alloy in which the sum of the contents of Al and Fe is 89 wt% or more.

12. In paragraph 9, The above-mentioned member is a hot-formed member having a coefficient of friction of 0.50 or less.

13. In paragraph 9, The above steel sheet contains, in weight %, carbon (C): 0.02 to 0.60%, silicon (Si): 0.001 to 2.000%, aluminum (Al): 0.001 to 1.000%, manganese (Mn): 0.1 to 4.0%, phosphorus (P): 0.050% or less, sulfur (S): 0.0200% or less, nitrogen (N): 0.0200% or less, titanium (Ti): 0 to 1.0000%, niobium (Nb): 0 to 1.0000%, vanadium (V): 0 to 1.0000%, boron (B): 0 to 0.0100%, chromium (Cr): 0 to 1.00%, molybdenum (Mo): 0 to 1.00%, tungsten (W): 0 to 1.00%, copper (Cu): A hot-formed member having a composition containing 0~1.0% nickel (Ni), 0~1.0% antimony (Sb), 0~1.00% tin (Sn), 0~1.00% calcium (Ca), 0~0.10% magnesium (Mg), 0~0.10% cobalt (Co), 0~1.00% arsenic (As), 0~1.00% zirconium (Zr), 0~1.00% bismuth (Bi), 0~1.00% rare earth elements (REM), 0~0.3%, the remainder iron (Fe), and other unavoidable impurities.

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