Hot-press-formed member, hot-press-formed parts, and methods for manufacturing same, and forming device, forming method, bracket for battery case, and battery pack module

Abstract

The purpose of the present invention is to provide a hot-press-formed member having excellent coating-corrosion resistance and a method for manufacturing same, the hot-press-formed member comprising a base steel and an aluminum-based alloy plated layer, wherein the base steel comprises, by wt%, 0.015-0.10% of Sb, and the aluminum-based alloy plated layer comprises an intermediate layer and an outermost layer positioned on the upper portion of the intermediate layer.

Description

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

[0001] The present invention relates to a hot-formed member, a hot (press)-formed part, and a method for manufacturing the same.

[0002] 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.

[0003] 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, one way to improve fuel efficiency is to reduce the thickness of steel sheets used. However, reducing thickness can compromise vehicle safety, so increasing the strength of the steel sheets is essential.

[0004] 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.

[0005] Furthermore, as mentioned above, attempts have been made to reduce vehicle weight by utilizing aluminum (Al) to improve fuel efficiency. However, when using an outer panel primarily composed of aluminum and an inner panel primarily composed of iron, thermal deformation and distortion are unavoidable due to the difference in coefficient of thermal expansion between the inner and outer panels.

[0006] To address this issue, some methods involve changing the type of adhesive used to bond parts or lowering the paint temperature. While this approach increases vehicle manufacturing time and reduces productivity, it is an effective means for weight reduction, and is currently being implemented on some vehicle models.

[0007] In response to the issues mentioned above, steel companies support automobile manufacturers by developing and supplying products that can easily be applied to processes for forming steel for manufacturing parts, such as hot press forming (HPF) or hot stamping.

[0008] 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.

[0009] This hot press forming method, when using a hot press forming method that forms at high temperatures, has an excellent characteristic of having an elongation of 50% or more at the high temperature where forming is performed, so that even parts with a small curvature radius can be formed without cracks, and thus the shape of the formed part that cannot be secured with cold ultra-high strength can be secured.

[0010] In addition, hot press-formed parts manufactured by hot-working (hot stamping) blanks can be manufactured into parts of various shapes compared to conventional giga-grade cold-formed materials because they are formed at high temperatures with excellent general formability.

[0011] Due to these characteristics, hot press forming is mainly applied to materials suitable for parts that serve as the vehicle frame, such as the A-pillar, center pillar, and roof side panel.

[0012] However, in the case of the hot press forming method, since the steel sheet must be heated to a high temperature, there was a problem in that the surface of the steel sheet oxidized, and therefore a process for removing the oxide on the surface of the steel sheet had to be added after the press forming. Patent Document 1 has been proposed as a method for solving this problem. In the invention, a steel sheet plated with aluminum is used in a process of heating and rapidly cooling after hot press forming or room temperature forming (briefly, 'post-heat treatment'). Since the aluminum plating layer exists on the surface of the steel sheet, the steel sheet does not oxidize when heated.

[0013] To hot press-form the aluminum-plated steel sheet described above, a step of heating the steel sheet is performed. During this step, the temperature of the steel sheet increases, resulting in diffusion of iron (Fe) from the base iron of the steel sheet into the plating layer on the surface, thereby causing alloying in the plating layer.

[0014] When hot press forming such aluminum-plated steel sheets, cracks can occur in the plating layer at the points where it comes into close contact with the mold during the pressing process. Furthermore, where bending occurs due to the pressing process, strong tensile stress is applied to the outermost surface of the plating layer. Due to the nature of the fragile alloy layer, this tensile stress can cause cracks to form from the surface. However, if the aluminum-plated layer is thin and the crack penetrates the plating layer, exposing the surface of the base steel sheet, the corrosion resistance of the resulting hot press-formed part can be reduced.

[0015] Meanwhile, steel that can be suitably subjected to hot press forming is a typical galvanized steel sheet, and an example thereof is an aluminum-based galvanized steel sheet manufactured through aluminum (Al) plating. When joining parts (hot-formed parts, components) obtained by forming such galvanized steel sheets, welding is generally the method of joining, but due to the surface properties of galvanized steel sheets, a joining process using a bonding agent may also be employed.

[0016] When bonding components using adhesives, structural sealers and mastic sealers can be used, depending on the specific characteristics of the component. When using these adhesives, each automaker has its own standards to ensure the quality of the bonding.

[0017] In this way, the adhesion evaluation during the bonding process using adhesives is usually conducted on a clean surface, but since foreign substances may adhere to the surface during the parts assembly or transportation process, the evaluation can be conducted by taking into account cases where surface foreign substances exist. This evaluation method is called 'oiled surface adhesion evaluation', and after the surface is degreased (cleaned), the rust preventive oil applied when the steel was shipped from the steel factory to prevent corrosion is reapplied, and then the adhesive is applied over it to conduct the evaluation. At this time, the rust preventive oil is a mixture of mineral oil, base oil, rust preventive agent, lubricant, etc., and generally has a negative effect on the curing mechanism of the adhesive. In particular, the rust preventive oil inhibits the chemical reaction at the interface between the plating layer and the adhesive, resulting in a loss in bonding strength and fracture shape. Accordingly, adhesive manufacturers producing related adhesives use porous inorganic additives to solve the aforementioned problems. However, if the amount of this inorganic additive used is excessive, the shear and impact strength of the adhesive decreases, resulting in a deterioration in quality. Therefore, the amount used is preferably not to exceed 30% by weight (Patent Document 2). In addition, if the amount of rust-preventive oil used is excessive, or if the molecular structure of the rust-preventive oil does not match the porous structure of the inorganic additive, it causes a loss of adhesive strength. Adhesives that exhibit these characteristics include Acrylonitrile Butadiene Styrene (ABS) rubber and adhesives containing a large amount of phthalate plasticizer.

[0018] When the surface of the plating layer of a hot-formed part obtained by hot-forming a steel sheet for hot press forming, such as an aluminum-plated steel sheet, has unevenness such as cracks, pores, or micro-blemishes, the anti-rust oil applied on the plating layer easily seeps into the gaps between the unevenness. This is because the surface tension is designed to be low. In addition, the pores existing on the surface of the plating layer are formed in a shape similar to a water bottle during the rolling process during the steel manufacturing process, so the anti-rust oil that seeps into these pores has a structure that makes it difficult for it to volatilize and come out.

[0019] Meanwhile, when hot press forming a plated steel sheet with a plating layer, pores are sometimes formed on the surface of the plating layer to prevent destruction due to hydrogen embrittlement. These pores are widely distributed not only on the surface of the plating layer but also within the steel, and their size varies depending on the heat treatment conditions of the steel.

[0020] In this way, if the anti-rust oil seeps into the pores present on the surface of the plating layer of the hot-formed part, it is not sufficiently volatilized during the curing process of the adhesive, and remains at the interface, causing a loss of adhesive strength.

[0021] Accordingly, there is a need to develop a method to improve adhesive performance when bonding hot-formed parts (components) that require the use of adhesives.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] Fig. 14 is a schematic diagram of a side frame of a battery case, and Fig. 15 is a cross-sectional view taken along line AA' of Fig. 14. As shown in Figs. 14 and 15, the side frame (B-1) of the battery case must have flanges formed at the top and bottom of the frame (B-10) in order to be connected to the upper and lower plates, and the same applies to the bracket (B-20). That is, the bracket (B-20) also includes a main body (B-23) and flanges (B-21, B-22) formed by bending from the main body (B-23). ​​The bracket (B-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 top and bottom.

[0027] When a part includes a curvature or dimensional transition, a stretch flange or a shrink flange is formed on the flange (B-21, B-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 or folds can create uneven gaps in the battery pack, potentially compromising its watertightness.

[0028] Meanwhile, in the case of the bracket (B-20), in order to ensure uniformity of strength and collision safety performance, it must be formed of the same material as the frame (B-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.

[0029] In the case of conventional cold forming steel plates, when the tensile strength becomes ultra-high strength steel of 980 MPa or more, 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] (Patent Document 1) U.S. Patent Publication No. 6296805

[0034] (Patent Document 2) Korean Patent Publication No. 10-2022-0089675

[0035] (Patent Document 3) U.S. Patent Publication No. 2014-0056754

[0036] (Patent Document 4) Korean Patent Publication No. 10-2020-006635

[0037] (Patent Document 5) Korean Patent Publication No. 10-2023-0092430

[0038] The first aspect of the present invention is to provide a hot-formed member having excellent paint corrosion resistance and a method for manufacturing the same.

[0039] The second aspect of the present invention is to provide a plated steel sheet having a controlled surface structure and a method for manufacturing the same so as to improve the sealer adhesion of a member (part) manufactured by hot press forming, in providing a steel sheet suitable for hot press forming.

[0040] A third 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.

[0041] The fourth 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.

[0042] A fifth aspect of the present invention is to provide a press-formed part and a method for manufacturing the same, in which damage such as cracks is minimized during hot press forming to manufacture a part having a plurality of hat shapes.

[0043] 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.

[0044] 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 steel sheet for hot forming and / or the manufacturing method thereof according to the first aspect of the present invention can be usefully applied to the hot forming members according to the second to fifth aspects, various parts obtained therefrom, and the manufacturing methods thereof. In addition, the manufacturing method of the parts according to the second aspect of the present invention, or the heat treatment conditions used therefor, can be usefully applied in the process of manufacturing the brackets or molded parts for battery cases according to the third to fifth 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.

[0045] A hot-formed member according to a first aspect of the present invention comprises a base steel; an aluminum-based alloy plating layer, wherein the base steel contains Sb in an amount of 0.015 to 0.10 wt%, the aluminum-based alloy plating layer includes an intermediate layer and an outermost layer positioned on the intermediate layer, and the Cr increase / decrease ratio (%) derived from the following relational expression 1 may be 5% or more.

[0046] [Relationship 1]

[0047]

[0048] (In the above relational expression 1, A means Crmax of the outermost layer, and B means Crmax of the intermediate layer.)

[0049] The above-mentioned base steel contains, in wt%, C: 0.080 to 0.50%, Si: 0.050 to 1.0%, Mn: 0.50 to 4.0%, P: 0.0150% or less (excluding 0%), S: 0.0200% or less (excluding 0%), Al: 0.010 to 0.10%, N: 0.02000% or less (excluding 0%), and Cr: 0.01 to 1%, and the remainder may be made of Fe and unavoidable impurities.

[0050] The above-described steel may further include one or more elements selected from the following a) to f).

[0051] a) At least one selected from titanium (Ti), niobium (Nb), zirconium (Zr) and vanadium (V): 0.005 to 0.400 wt%,

[0052] b) Boron (B): 0.0001 to 0.0100 wt%,

[0053] c) At least one of molybdenum (Mo) and tungsten (W): 0.001 to 1.000 wt%,

[0054] d) At least one of copper (Cu) and nickel (Ni): 0.003 to 2.000 wt%,

[0055] e) One or more types of tin (Sn): 0.001 to 1.000 wt%

[0056] f) Rare earth elements (REM): 0.0200 wt% or less

[0057] The Simax of the above-described intermediate layer may be 5.5 wt% or more and 15 wt% or less.

[0058] The hot-formed member described above may have a total width of the left and right corrosion blisters of 5.0 mm or less after electroplating and coating corrosion resistance evaluation.

[0059] A method for manufacturing a hot-formed member according to another aspect of the present invention may include the steps of preparing a base steel containing 0.015 to 0.10 wt% of Sb; immersing the base steel in an aluminum-based plating bath to obtain an aluminum-based plated steel; heating and maintaining the aluminum-based plated steel at a temperature of Ae3 or higher to obtain an aluminum-based alloy-plated steel; and cooling the aluminum-based alloy-plated steel after hot forming, and may satisfy the following relational expression 2.

[0060] [Relationship 2]

[0061]

[0062] (In the above relational expression 2, t total is the total heating time (sec) in the furnace during the above heating, Ae3 is the equilibrium temperature (℃) at which transformation to austenite is completed, and T furnace refers to the set temperature (℃) inside the furnace during the above heating.)

[0063] The above-mentioned base steel contains, in wt%, C: 0.080 to 0.50%, Si: 0.050 to 1.0%, Mn: 0.50 to 4.0%, P: 0.0150% or less (excluding 0%), S: 0.0200% or less (excluding 0%), Al: 0.010 to 0.10%, N: 0.02000% or less (excluding 0%), and Cr: 0.01 to 1%, and the remainder may be made of Fe and unavoidable impurities.

[0064] The above-described steel may further include one or more elements selected from the following a) to f).

[0065] a) At least one selected from titanium (Ti), niobium (Nb), zirconium (Zr) and vanadium (V): 0.005 to 0.400 wt%,

[0066] b) Boron (B): 0.0001 to 0.0100 wt%,

[0067] c) At least one of molybdenum (Mo) and tungsten (W): 0.001 to 1.000 wt%,

[0068] d) At least one of copper (Cu) and nickel (Ni): 0.003 to 2.000 wt%,

[0069] e) One or more types of tin (Sn): 0.001 to 1.000 wt%

[0070] f) Rare earth elements (REM): 0.0200 wt% or less

[0071] The cooling rate in the above-described cooling step can be 10 to 1000°C / s.

[0072] Although not essential, the 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.

[0073] According to a second aspect of the present invention, a hot-formed member is provided, comprising: a base steel plate; and an aluminum (Al)-based plating layer formed on at least one surface of the base steel plate, wherein the aluminum (Al)-based plating layer has an oxide layer including aluminum oxide having a thickness of 100 nm or less from the surface.

[0074] In one embodiment of the present invention, the oxide layer has surface pores of 30 / 100㎛. 2 Exceeding ~80 / 100㎛ 2 Below, the distribution of aluminum oxide can be 90-100%.

[0075] In this way, by increasing the amount of aluminum oxide distributed in the pores present on the surface of the plating layer according to the number of pores, the adhesive performance of the hot-formed part can be improved.

[0076] In one embodiment of the present invention, the oxide layer has surface pores of 30 / 100㎛. 2 Below, the distribution of aluminum oxide may be 70% or more.

[0077] In one embodiment of the present invention, the steel sheet may contain, in wt%, carbon (C): 0.17 to 0.32%, silicon (Si): 0.50% or less, manganese (Mn): 1.0 to 2.3%, aluminum (Al): 0.010% or less, phosphorus (P): 0.030% or less, sulfur (S): 0.005% or less, boron (B): 0.0005 to 0.0040%, titanium (Ti): 0.020 to 0.055%, the remainder being Fe and other unavoidable impurities.

[0078] In one embodiment of the present invention, the aluminum-based plating layer may be composed of, in weight %, silicon (Si): 7.0 to 10.0%, iron (Fe): 5.0 to 15.0%, the remainder aluminum (Al), and other unavoidable impurities.

[0079] In one embodiment of the present invention, the aluminum-based plating layer may further include one or more elements selected from the group consisting of the following i) to iii).

[0080] i) One or more of chromium (Cr) and molybdenum (Mo): 2.5% or less

[0081] ii) One or more of niobium (Nb), zirconium (Zr), and vanadium (V): 0.1% or less

[0082] iii) Antimony (Sb): 0.02~0.03%

[0083] According to another aspect of the present invention, a method for manufacturing a hot-formed part is provided, comprising the steps of: preparing a plated steel sheet having an aluminum-based plated layer on at least one surface of a base steel sheet; heating the plated steel sheet to a temperature range of 900 to 960°C at a heating rate of 15 to 20°C / s; maintaining the heated plated steel sheet for 3 to 6 minutes; and forming and rapidly cooling the plated steel sheet after the maintaining step.

[0084] In this way, when performing high-temperature heating for hot forming on a plated steel sheet having an aluminum-based plating layer, the distribution of aluminum oxide according to the number of pores can be controlled as desired by controlling the heating rate, the range of the heating temperature, and the holding time.

[0085] In one embodiment of the present invention, the rapid cooling can be performed at a cooling rate of 0°C / s or more.

[0086] Although not necessarily essential, the hot-formed member according to the second aspect of the invention can secure improved performance when combined with the advantageous features of the other aspects described below.

[0087] A third aspect of the present invention provides a molding device. The molding device 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, It comprises 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 upper positions of the third body forming portion and 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.

[0088] 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).

[0089] 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.

[0090] In one embodiment of the present invention, the punch may include a support portion that supports the pre-molding material outside the first and fifth molding portions with the third punch molding portion as the center.

[0091] 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.

[0092] 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.

[0093] 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°.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] In one embodiment of the present invention, the material may be the aforementioned hot-forming steel sheet or a hot-formed member obtained by hot-forming the hot-forming steel sheet. As an example, the hot-forming steel sheet and the hot-formed member may have the aforementioned alloy composition and may be manufactured using the aforementioned manufacturing method.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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°.

[0105] A bracket for a battery case according to one embodiment of the present invention can be manufactured using the molding method described above.

[0106] 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.

[0107] Although not necessarily essential, the article according to the third aspect of the invention may achieve further improved performance when combined with the advantageous features of the other aspects described below.

[0108] A fourth aspect of the present invention provides a high-strength steel hot press-formed part. The high-strength steel hot press-formed part includes 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 formed integrally, and the following [Relational Expression 3] is satisfied.

[0109] [Relationship 3]

[0110] Wall height (hw) ≤ 13.4 * wall angle (θw) + 182.4

[0111] (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.)

[0112] In one embodiment of the present invention, the high-strength steel may be the hot-forming steel plate described above.

[0113] According to one embodiment of the present invention, a molded part having high tensile strength and small curvature can be provided.

[0114] 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.

[0115] In one embodiment of the present invention, the molded part may have a tensile strength of 1300 to 2100 MPa.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] In one embodiment of the present invention, a plurality of hot press-formed parts may be arranged at regular intervals within the battery case.

[0122] Although not necessarily essential, the components according to the fourth aspect of the invention can be combined with the advantageous features of the other aspects described below to achieve further improved performance.

[0123] A fifth aspect of the present invention provides a press-formed part. The press-formed part has 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 deformed portions having a preset height, and a flat plate portion arranged between the plurality of deformed portions, connecting two adjacent boundary portions, and having a preset length.

[0124] 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.

[0125] 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 [Relationship 4], where w≤114.85e 0.0455h ... [Relationship 4], in the above [Relationship 4], w may mean the preset length, and h may mean the preset height.

[0126] In one embodiment of the present invention, the deformation portion is provided in four or more, and the relationship between the preset length and the preset height is defined by the following [Relationship Expression 5], and w≤46.309e 0.105h ... [Relationship 5], in the above [Relationship 5], w may mean the preset length, and h may mean the preset height.

[0127] In one embodiment of the present invention, the preset length (w) may be 20 mm or more.

[0128] In one embodiment of the present invention, the press-formed part can be manufactured using a hot press forming method.

[0129] In one embodiment of the present invention, the hot press forming method may be the method described above.

[0130] 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.

[0131] In one embodiment of the present invention, the metal plate may be the hot forming steel plate described above.

[0132] In one embodiment of the present invention, the press forming step may use the above-described forming device.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] According to one aspect of the present invention, a hot-formed member having excellent paint corrosion resistance and a method for manufacturing the same can be provided.

[0141] According to another aspect of the present invention, in providing a hot-formed member, a hot-formed member with improved adhesive performance can be provided.

[0142] 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 weight reduction, watertightness, and collision safety performance of a battery pack.

[0143] According to another aspect of the present invention, it is possible to provide a molded part having high tensile strength, small curvature, and being easy to process because it can be manufactured at one time, and also to manufacture a part with high space utilization when manufacturing a module such as a battery pack.

[0144] According to another aspect of the present invention, a press forming process can be performed on a metal plate by placing an intermediate press portion having a height difference between upper and lower molds, and using three press portions. 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 on 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.

[0145] 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.

[0146] In order to more fully understand the drawings cited in the detailed description of the present invention, a brief description of each drawing is provided.

[0147] Fig. 1 is an SEM photograph of a hot-formed member of Invention Example A-3.

[0148] Fig. 2 is an SEM photograph of the hot-formed member of Invention Example A-4.

[0149] Figure 3 is an SEM photograph of the hot-formed member of Comparative Example A-2.

[0150] Figure 4 is a photograph of a corroded paint blister after the paint corrosion resistance evaluation of Invention Example A-6.

[0151] Figure 5 is a photograph of a corroded paint blister after the paint corrosion resistance evaluation of Comparative Example A-4.

[0152] Figure 6 is a graph showing the GDS observation results of invention example A-6.

[0153] Figure 7 is a graph showing the GDS observation results of Comparative Example A-4.

[0154] Fig. 8 is a photograph showing a cross-section of a plating layer of a hot-formed member (inventive steel) according to one embodiment of the present invention, and (b) is an enlarged photograph of (a).

[0155] FIG. 9 shows a photograph of the surface of a plating layer of a hot-formed member according to one embodiment of the present invention, and a photograph of a cross-section in the thickness direction (the numbers in the cross-sectional photograph of FIG. 9 indicate the thickness from the outermost layer to the base iron interface and the thickness of the diffusion layer).

[0156] Fig. 10 is a graph showing the number of pores present on the surface of a plating layer of a hot-formed member according to one embodiment of the present invention.

[0157] Fig. 11 is a graph showing the results of measuring the surface of a plating layer of a hot-formed part according to one embodiment of the present invention using XPS.

[0158] FIG. 12 shows photographs of the surfaces observed over time after applying anti-rust oil to each surface to evaluate the adhesiveness of a hot-formed member according to one embodiment of the present invention.

[0159] Fig. 13 shows the results of adhesive evaluation of a hot-formed part according to one embodiment of the present invention, showing the results of adhesive strength according to the amount of oil applied (a) and the results of observing adhesive surface residue according to the amount of oil applied (b).

[0160] Figure 14 is a schematic diagram of the side frame of the battery case.

[0161] Figure 15 is a cross-sectional view taken along line A-A' of Figure 10.

[0162] Figure 16 is an exploded perspective view of a molding device according to one embodiment of the present invention.

[0163] Figure 17 is a side view of a molding device according to one embodiment of the present invention.

[0164] Figure 18 is a flowchart of a molding method according to one embodiment of the present invention.

[0165] Figure 19 is a plan view of a material fed into a molding device according to one embodiment of the present invention.

[0166] FIG. 20 is a schematic perspective view showing a first molding step in a molding method according to one embodiment of the present invention.

[0167] Fig. 21 is a schematic perspective view showing a second forming step in a forming method according to one embodiment of the present invention.

[0168] FIG. 22a is a perspective view showing the second molding step in a molding method according to one embodiment of the present invention from another direction, and FIG. 22b is a front view showing the second molding step in a molding method according to one embodiment of the present invention.

[0169] Fig. 23 is a front view showing a cooling step in a molding method according to one embodiment of the present invention.

[0170] Fig. 24 is a perspective view showing a trimming step in a molding method according to one embodiment of the present invention.

[0171] Figure 25 is a perspective view of a bracket manufactured using a molding method according to one embodiment of the present invention.

[0172] Figure 26 is a thickness reduction rate distribution diagram of a molded product manufactured using a molding method according to one embodiment of the present invention.

[0173] Figure 27 is a thickness reduction rate distribution diagram of a molded product manufactured using the molding method of Comparative Example 1-1.

[0174] Fig. 28 is a graph of the thickness reduction rate distribution in the cross section of the molded products of Figs. 26 and 27.

[0175] Figure 29 is a side view showing the forming method of Comparative Example 1-2.

[0176] Figure 30 is a perspective view of a molded product manufactured using the molding method of Comparative Example 1-2.

[0177] Figure 31 is a perspective view of a molded part according to one embodiment of the present invention.

[0178] Figure 32 is a front view of a molded part according to one embodiment of the present invention.

[0179] FIGS. 33a, 33b, 34a, and 34b are drawings showing an interpretation according to an embodiment and a comparative example of the present invention. Referring to Table 1, FIG. 33a shows invention example 2-1, FIG. 33b shows comparative example 2-1, FIG. 34a shows invention example 2-3, and FIG. 34b shows comparative example 2-3.

[0180] Figure 35 is a perspective view of a battery pack module according to one embodiment of the present invention.

[0181] FIG. 36 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 the 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).

[0182] Fig. 37 is a perspective view illustrating a press-molded part according to one embodiment of the present invention.

[0183] Figure 38 is a perspective view illustrating a press-formed part according to another embodiment of the present invention.

[0184] Fig. 39 (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. 39 (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.

[0185] Fig. 40 (a) is an example showing a strain applied to a press-formed part manufactured using a conventional manufacturing method, and Fig. 40 (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.

[0186] Figure 41 is a flowchart showing a method for manufacturing a press-molded part according to one embodiment of the present invention.

[0187] Figure 42 schematically illustrates the first step of manufacturing the press-formed part of Figure 37.

[0188] Figure 43 schematically illustrates the second step of manufacturing the press-formed part of Figure 37.

[0189] Figure 44 schematically illustrates the third step of manufacturing the press-formed part of Figure 37.

[0190] Figure 45 schematically illustrates the fourth step of manufacturing the press-formed part of Figure 37.

[0191] Figure 46 schematically illustrates the first step of manufacturing the press-formed part of Figure 38.

[0192] Figure 47 schematically illustrates the second step of manufacturing the press-formed part of Figure 38.

[0193] Figure 48 schematically illustrates the third step of manufacturing the press-formed part of Figure 38.

[0194] Figure 49 schematically illustrates the fourth step of manufacturing the press-formed part of Figure 38.

[0195] Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0196] In this specification, the term "including" is used to indicate that other components may be included rather than excluding other components unless specifically stated to the contrary.

[0197] Additionally, unless otherwise specifically provided in the specification of the present invention, the % unit means weight%.

[0198] Hot-formed parts used as materials for automobiles, etc. need to ensure corrosion resistance, and the inventors of the present invention recognized that the chromium content in the plating layer is an important factor in improving the corrosion resistance of the hot-formed parts.

[0199] Accordingly, the inventors of the present invention have conducted in-depth research and have found that by adding antimony (Sb) to steel, a concentrated layer can be formed at the interface between the base steel and the aluminum-based plating layer during hot forming, and the diffusion rate of chromium within the plating layer can be controlled. This increases the chromium content of the outermost layer and reduces the chromium content of the intermediate layer, thereby preventing localized corrosion resistance degradation after alloying of the hot-formed member. As a result, the inventors have discovered that the phenomenon of corrosion sites being formed and corrosion accelerating due to the aforementioned localized corrosion resistance degradation can be prevented, and this has led to the completion of the present invention.

[0200] In addition, the inventors of the present invention have confirmed that a hot-formed member capable of improving sealer adhesion can be provided, and have thus provided the present invention.

[0201] Below, before describing in detail a hot-formed member according to an embodiment of the present invention, an aluminum-based plated steel material for hot pressing according to an embodiment of the present invention will first be described.

[0202] The aluminum-based plated steel for hot pressing of the present invention may have a base steel and an aluminum-based plated layer formed on the surface thereof.

[0203] In particular, as described above, the steel according to an example of the present invention may include Sb: 0.015 to 0.10% by weight.

[0204] Sb in the base steel can form a concentrated layer at the base steel-plating layer interface during hot forming, and can reduce the Cr content concentrated in the intermediate layer by changing the diffusion rate of Cr in the aluminum-based plating layer. As a result, as described above, the corrosion resistance of the hot-formed member can be improved. If the Sb content is less than 0.015%, the above-described effect cannot be obtained. As another example, the base steel of the present invention can contain 0.018% or more of the Sb, and as another example, it can contain 0.022% or more.

[0205] On the other hand, if the Sb content exceeds 0.10%, the hydrogen embrittlement resistance and bendability of the hot-formed member may deteriorate due to excessive grain boundary segregation of Sb. As another example, the base steel of the present invention may contain 0.097% or less of the Sb, and as another example, may contain 0.094% or less.

[0206] In addition, the alloy composition of the above-described base steel is not particularly limited, but according to a non-limiting example, the above-described base steel may include, in wt%, C: 0.080 to 0.50%, Si: 0.050 to 1.0%, Mn: 0.50 to 4.0%, P: 0.0150% or less (excluding 0%), S: 0.0200% or less (excluding 0%), Al: 0.010 to 0.10%, N: 0.02000% or less (excluding 0%), Cr: 0.01 to 1%, and the remainder may be made of Fe and unavoidable impurities. Hereinafter, each alloy component will be described in detail.

[0207] C: 0.080~0.50%

[0208] The above C is an essential element for increasing the strength of a hot-formed member and can be added in an appropriate amount. That is, in order to sufficiently secure the strength of a hot-formed member, the C can be added in an amount of 0.080% or more. Preferably, the lower limit of the C content can be 0.095% or more. However, if the content is too high, when producing a cold-rolled member, the strength of the hot-rolled member will be too high when cold-rolling the hot-rolled member, resulting in greatly inferior cold-rollability and greatly reduced spot weldability. Therefore, in order to secure sufficient cold-rollability and spot weldability, it can be added to 0.50% or less. In addition, the C content can be 0.45% or less, and more preferably, the content can be limited to 0.40% or less.

[0209] Si: 0.050~1.0%

[0210] The above-mentioned Si should not only be added as a deoxidizer in steelmaking, but also plays a role in suppressing the formation of carbides, which has the greatest influence on the strength of hot-formed parts. In the present invention, in order to secure retained austenite by concentrating carbon in the martensite lath grain boundaries after the formation of martensite in hot press forming, it may be added in a content of 0.050% or more. In addition, in order to secure sufficient plating properties when aluminum plating is performed on a steel sheet after rolling, the upper limit of the Si content may be set to 1.0%. Preferably, the Si content may be limited to 0.85% or less.

[0211] Mn: 0.50~4.0%

[0212] The above Mn can be added in an amount of 0.50% or more to not only secure a strengthening effect but also lower the critical cooling rate for securing martensite in hot-formed parts. In addition, the Mn content can be limited to 4.0% or less in order to secure the workability of the hot press forming process, reduce manufacturing costs, and improve spot weldability by appropriately maintaining the strength of the steel plate. Preferably, the Mn content can be 3.0% or less, and in some cases, it can be 2.0% or less.

[0213] P: 0.0150% or less (excluding 0%)

[0214] The above P exists as an impurity in the steel, and the lower its content is, the more advantageous it is. Therefore, in the present invention, the P content may be limited to 0.0150% or less, and preferably may be limited to 0.0130% or less. Since P is an impurity element that is advantageous the less it is, there is no need to specifically set an upper limit for its content. However, considering that the above P may inevitably be included in the base steel, a case where the above P is included at 0% may be excluded from the scope of the present invention.

[0215] S: 0.0200% or less (excluding 0%)

[0216] The above S is an impurity in steel and is an element that hinders the ductility, impact properties and weldability of the member, so the maximum content is limited to 0.0200%, and preferably limited to 0.0100% or less. Since the lower the content of the above S, the more advantageous it is for securing the ductility, impact properties and weldability of the member, the lower limit thereof is not specifically limited. However, considering that the above S may inevitably be included in the base steel, a case where the above S is not included at all may be excluded from the scope of the present invention.

[0217] Al: 0.010~0.10%

[0218] The above Al, together with Si, can improve the cleanliness of steel by performing a deoxidation function in steelmaking, and can be added in a content of 0.010% or more to achieve the above effect. In addition, the content of the above Al can be limited to 0.10% or less to prevent the Ac3 temperature from becoming too high and to allow the heating required for hot press forming to be performed within an appropriate temperature range.

[0219] N: 0.02000% or less (excluding 0%)

[0220] The above N is an element included as an impurity in steel, and in order to reduce the sensitivity to crack occurrence during continuous slab casting and to secure impact properties, the lower the content is, the more advantageous it is. Therefore, it can be included at 0.02000% or less. Since the lower the content of the above N, the more advantageous it is for securing impact properties, the lower the content is not specifically limited. However, considering that the above N may inevitably be included in the base steel, a case where the above N is not included at all can be excluded from the scope of the present invention.

[0221] Cr: 0.010~1.0%

[0222] The above Cr is an element that increases the hardenability of steel, and in order to achieve the effect of improving the corrosion resistance of the paint through the diffusion of the plating layer when manufacturing the cold-rolled steel sheet and member according to an example of the present invention, the Cr may be included in an amount of 0.010% or more. As another example, the Cr may be included in an amount of 0.050% or more. However, when the Cr is included in excess in the cold-rolled steel sheet, not only may the cost increase, but also the problem of deterioration of the physical properties due to excessive generation of Cr-based carbides may occur. Therefore, in an example of the present invention, the upper limit of the Cr content may be set to 1.0%. As another example, the Cr may be included in an amount of 0.90% or less, and as another example, the Cr may be included in an amount of 0.80% or less.

[0223] A cold rolled steel sheet according to an example of the present invention may optionally, if necessary, further include one or more elements selected from among the following a) to f) in addition to the steel composition described above.

[0224] a) At least one selected from titanium (Ti), niobium (Nb), zirconium (Zr), and vanadium (V): 0.00500 to 0.400 wt%

[0225] The above Ti, Nb, Zr and V are effective in improving the strength of steel plates for hot-formed parts by forming fine precipitates and in stabilizing retained austenite and improving impact toughness by refining crystal grains, so one or more of these may be added in a total content of 0.00500% or more. However, if the addition amount exceeds 0.400%, not only will the effect be saturated, but excessive addition of alloy iron may also result in an increase in cost.

[0226] b) Boron (B): 0.0001000~0.01000 wt%

[0227] The above B is an element that can not only improve hardenability even with a small amount of addition, but can also suppress embrittlement of hot-formed parts due to grain boundary segregation of P and / or S by segregating at the grain boundaries of old austenite. Therefore, B can be added in an amount of 0.0001000% or more. However, if it exceeds 0.01000%, not only will the effect be saturated, but it will also cause embrittlement in hot rolling, so the upper limit can be set to 0.01000%, and in one implementation example, the B content can be set to 0.005000% or less.

[0228] c) At least one of molybdenum (Mo) and tungsten (W): 0.0010 to 1.0 wt%

[0229] Since the above Mo and W can improve hardenability and secure strength and grain refinement through the precipitation strengthening effect, one or more of these can be added in an amount of 0.0010% or more based on the total content. In addition, the content can be limited to 1.0% or less to secure the weldability of the member.

[0230] d) At least one of copper (Cu) and nickel (Ni): 0.0030 to 2.0 wt%,

[0231] The above Cu and Ni are elements that enhance strength by forming fine precipitates. To achieve the above-described effects, the sum of one or more of these elements may be set to 0.0030% or more. However, since exceeding 2.0% would result in excessive cost increases, the upper limit may be set at 2.0%.

[0232] e) Tin (Sn): 0.0010~1.0 wt%

[0233] The above Sn can improve plating properties by concentrating on the surface during annealing heat treatment for Al-Si plating and suppressing the formation of Si or Mn oxides on the surface. To achieve this effect, it can be added in an amount of 0.0010% or more. However, if the amount added exceeds 1.0%, not only will it incur excessive alloying costs, but it can also be dissolved in slab grain boundaries, causing coil edge cracks during hot rolling. Therefore, the upper limit is set at 1.0%.

[0234] f) Rare earth elements (REM): 0.020 wt% or less

[0235] The above REM is an element that is inevitably included, and if the above REM is excessively included in the cold-rolled steel sheet, a problem of deterioration in the properties of the hot-formed member may occur. Therefore, in one example of the present invention, the upper limit of the REM content may be set to 0.020%.

[0236] Other than the components described above, the remaining components include iron (Fe) and unavoidable impurities. In addition, if the components can be included in the base steel of the aluminum-based plating steel for hot pressing, there are no special restrictions on additional additions.

[0237] The aluminum-based plated steel according to the embodiment may have an aluminum-based plated layer formed on the surface of the base steel.

[0238] In addition, but not necessarily limited thereto, as an example, the aluminum-based plating layer may include Si: 5.0 to 11% by weight, with the remainder being Al and other unavoidable impurities, when the remaining alloy composition excluding the Fe content diffused from the cold-rolled steel sheet is 100%.

[0239] Next, a method for manufacturing an aluminum-based plated steel according to an embodiment is described in detail.

[0240] The embodiment can be manufactured by preparing a steel having the above composition and then performing molten aluminum plating.

[0241] The type of the above-mentioned steel is not particularly limited to hot-rolled steel sheet, cold-rolled steel sheet, annealed steel sheet, etc., and any steel that can be applied in the technical field of the present invention is sufficient.

[0242] Meanwhile, the composition of the molten aluminum plating bath may include, in weight %, 5.0 to 11% of Si and 5.0% or less of Fe, with the remainder being Al and other unavoidable impurities.

[0243] Hereinafter, the hot-formed member of the present invention will be described in detail.

[0244] A hot-formed member according to one embodiment of the present invention may include a base steel; an aluminum-based alloy plating layer, and the base steel may include 0.015 to 0.10 wt% of Sb. In addition, the aluminum-based alloy plating layer may include an intermediate layer and an outermost layer positioned on the intermediate layer, and the Cr increase / decrease rate (%) derived from the following relational expression 1 may be 5% or more. Hereinafter, each component will be described in detail.

[0245] [Relationship 1]

[0246]

[0247] (In the above relational expression 1, A means Crmax of the outermost layer, and B means Crmax of the outermost layer.)

[0248] A hot-formed member according to one embodiment of the present invention may include a base steel, and the base steel may include Sb in an amount of 0.015 to 0.10 wt% as described above. In addition, although not necessarily limited thereto, the base steel may include C: 0.080 to 0.50 wt%, Si: 0.050 to 1.0 wt%, Mn: 0.50 to 4.0 wt%, P: 0.0150 wt% or less (excluding 0%), S: 0.0200 wt% or less (excluding 0%), Al: 0.010 to 0.10 wt%, N: 0.02000 wt% or less (excluding 0%), and Cr: 0.01 to 1 wt%, with the remainder being Fe and unavoidable impurities. In addition, as a non-limiting example, the base steel may further include one or more elements selected from the following a) to f).

[0249] a) At least one selected from titanium (Ti), niobium (Nb), zirconium (Zr) and vanadium (V): 0.005 to 0.400 wt%,

[0250] b) Boron (B): 0.0001 to 0.0100 wt%,

[0251] c) At least one of molybdenum (Mo) and tungsten (W): 0.001 to 1.000 wt%,

[0252] d) At least one of copper (Cu) and nickel (Ni): 0.003 to 2.000 wt%,

[0253] e) One or more types of tin (Sn): 0.001 to 1.000 wt%

[0254] f) Rare earth elements (REM): 0.0200 wt% or less

[0255] Since this has been described above in relation to aluminum-plated steel, it will be omitted.

[0256] Additionally, a hot-formed member according to a non-limiting example of the present invention may include an aluminum-based alloy plating layer.

[0257] Such an aluminum-based alloy plating layer can be obtained by performing an alloying heat treatment on the above-described aluminum-based plating layer, then heat-treating the obtained plated steel sheet at a temperature range of 880 to 950°C for 3 to 10 minutes, and then hot press forming.

[0258] That is, a hot-formed member according to a non-limiting example of the present invention may include an aluminum-based alloy plating layer obtained by alloying an aluminum-based plating layer with a component such as Fe of the base steel having the above-described composition on the surface of the base steel. The aluminum-based alloy plating layer may include an intermediate layer enriched with Si and an outermost layer positioned on the intermediate layer.

[0259] As illustrated in Fig. 1, the hot-formed member may include a diffusion layer, an intermetallic compound layer, an intermediate layer, and an outermost layer from the base steel. Here, the intermediate layer refers to a continuous or discontinuous layer containing concentrated Si.

[0260] As a non-limiting example, the Simax content of the intermediate layer may be 5.5 to 15 wt%. The Simax content of the intermediate layer refers to the maximum value of the Si content contained in the intermediate layer and can be measured by a Glow Discharge Spectrometer (GDS). The Si of the intermediate layer plays an important role in not only stabilizing the phase of the intermediate layer but also inhibiting grain growth. Therefore, it is difficult to expect the above effect when the Simax content is less than 5.5 wt%, and in order to exceed 15%, an excessive amount of Si content must be added to the plating bath, and the blank must be heat-treated at a very high temperature for a long time, which causes the diffusion layer to become excessively thick, which causes a problem of poor spot weldability.

[0261] In addition, but not necessarily limited thereto, as an example, the aluminum-based alloy plating layer may include Si: 5.0 to 11% by weight, with the remainder being Al and other unavoidable impurities, when the remaining alloy composition excluding the Fe content diffused from the base steel is 100%.

[0262] Meanwhile, a hot-formed member according to an example of the present invention may have a Cr increase / decrease rate (%) derived from the following relational expression 1 of 5% or more.

[0263] [Relationship 1]

[0264]

[0265] (In the above relational expression 1, A means Crmax of the outermost layer, and B means Crmax of the intermediate layer.)

[0266] In order to prevent the problem of localized reduction in corrosion resistance due to an increase in the chromium content in the intermediate layer formed after alloying of an aluminum-plated hot-formed member, a hot-formed member according to an example of the present invention essentially adds antimony (Sb) to the base steel, and the Cr increase / decrease rate (%) derived from the following relational expression 1 can be 5% or more.

[0267] The higher the Cr increase / decrease rate (%) described above, the more advantageous it is for achieving the purpose of the present invention, and therefore, the upper limit thereof is not specifically limited. However, in reality, the Cr increase / decrease rate (%) cannot increase indefinitely, and in one example of the present invention, the upper limit of the Cr increase / decrease rate (%) may be set to 50%.

[0268] As a result, the hot-formed member according to one embodiment of the present invention described above can secure excellent corrosion resistance after painting. More specifically, the hot-formed member according to one embodiment of the present invention can have a total left and right width of the corrosion blister after electrodeposition painting and paint corrosion resistance evaluation of 5.0 mm or less. In another example, it can be 4.8 mm or less, and in another example, it can be 4.5 mm or less.

[0269] Hereinafter, a method for manufacturing a hot-formed member of the present invention will be described in detail. However, the following method for manufacturing a hot-formed member is merely an example, and it is not necessary for the hot-formed member 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.

[0270] A method for manufacturing a hot-formed member according to one embodiment of the present invention may include a step of heating and maintaining the above-described aluminum-based plated steel to obtain an aluminum-based alloy plated steel; and a step of cooling the aluminum-based alloy plated steel after hot forming.

[0271] Below, each step is explained in detail.

[0272] First, a method for manufacturing a hot-formed member according to one embodiment of the present invention can prepare an aluminum-based plated steel material as described above in this specification, and heat and maintain the same to obtain an aluminum-based alloy plated steel material.

[0273] In addition, one embodiment of the present invention may set the temperature during the heating and maintenance to Ae3 or higher. This is to ensure sufficient strength by generating full austenite during heating and full martensite after hot forming. As another example, the lower limit of the temperature may be (Ae3+5)°C or (Ae3+10)°C.

[0274] At this time, the following equation can be applied to calculate Ae3, which is the equilibrium temperature at which the austenite transformation of each steel type is completed.

[0275] Ae3 = 912-370C-27.4Mn+27.3Si-6.35Cr+190Ti+72Al+332S+276P-900B+16.2CMn+32.3CSi+15.4CCr+4.32SiCr+174C 2 +2.46Mn 2 -6.86Si 2 +0.322Cr 2

[0276] In addition, a method for manufacturing a hot-formed member according to a non-limiting example of the present invention can satisfy the following relational expression 2 during the heating.

[0277] [Relationship 2]

[0278]

[0279] (In the above relational expression 2, t total is the total heating time (sec) in the furnace during the above heating, Ae3 is the equilibrium temperature (℃) at which transformation to austenite is completed, and T furnace refers to the set temperature (℃) inside the furnace during the above heating.)

[0280] One example of the present invention is that sufficient alloying of the aluminum-based plating layer can occur during the heating for hot forming through the above relationship 2, thereby obtaining an aluminum-based alloy plating steel. If the above relationship 2 is not satisfied during the heating, a problem may arise where a partially unalloyed region remains and the electrodeposition paintability is significantly reduced.

[0281] Next, one embodiment of the present invention may include a step of cooling an aluminum-based alloy plated steel after hot forming.

[0282] According to one example of the present invention, the cooling rate in the cooling step may be 10 to 1000°C / s.

[0283] If the cooling rate is less than 10°C / s, problems such as deterioration of tensile properties and bendability due to introduction of a ferrite phase during cooling may occur. Therefore, in one example of the present invention, the lower limit of the cooling rate may be set to 10°C / s. In another example, the lower limit of the cooling rate may be 15°C / s or 20°C / s.

[0284] On the other hand, if the cooling rate exceeds 1000°C / s, the shape of the molded part may be distorted, and there is a concern that the process cost for maintaining a high cooling rate may increase excessively. Therefore, in one example of the present invention, the cooling rate in the cooling step may be set to 1000°C / s or less. In another example, the upper limit of the cooling rate may be 900°C / s or 800°C / s.

[0285] Meanwhile, according to another aspect of the present invention, a hot-formed member including a steel plate and an aluminum (Al)-based plating layer formed on at least one surface of the steel plate can be provided.

[0286] In one embodiment of the present invention, the aluminum (Al)-based plating layer may include an oxide layer of 100 nm or less in the thickness direction from the surface.

[0287] A hot-formed part can be obtained by heating a hot-formed steel plate, or in one embodiment of the present invention, an aluminum-based plated steel plate, to a high temperature and then forming it. As will be described in detail later, according to one embodiment of the present invention, heating is performed at a relatively rapid temperature increase rate to a target temperature, then maintained for a certain period of time, and then rapid cooling is performed together with forming. As a result, an oxide layer may exist on the surface of the plated layer of the hot-formed part.

[0288] In one embodiment of the present invention, the oxide layer may mainly include aluminum oxide, as aluminum (Al), which is the main component constituting the plating layer, reacts with moisture, oxygen, etc. during a series of processes for hot forming to form oxide. Here, "mainly including" means including 50% or more of the total 100 wt% of components constituting the oxide layer. Meanwhile, the oxide layer is basically composed of aluminum oxide, but oxides due to oxidizing elements (e.g., Si, Mn, etc.) present in other plating layers may also be present.

[0289] In one embodiment of the present invention, the aluminum-based plating layer may sequentially include a diffusion layer (a), an alloy layer (b), an intermediate layer (c), and an outermost layer (d), which can be confirmed by the cross-sectional structure shown in Fig. 8 as an example. At this time, the layer forming an interface with the base steel plate is the diffusion layer (a), and the oxide layer may exist in the thickness direction from the surface of the outermost layer (d).

[0290] Meanwhile, in one embodiment of the present invention, the oxide layer present in the outermost layer (d) of the aluminum-based plating layer may have pores on its surface.

[0291] When using plated steel sheets with an aluminum plating layer as a material for automobiles, the hot-formed parts obtained by hot-forming the plated steel sheets may have pores on their surface, i.e., the surface of the plating layer. When applying a rust-preventive oil to the surface of such a hot-formed part, the rust-preventive oil may seep into the pores present on the surface of the plating layer, which may lower the performance of the adhesive applied for the subsequent bonding process. In addition, dust, foreign substances, etc. may easily enter the pores present on the surface of the plating layer, which may lower the adhesive strength of the adhesive. In particular, when the type of adhesive is a structural adhesive (structural sealer) or a mastic adhesive (mastic sealer), an epoxy resin is included for the purpose of improving the adhesive strength. However, this resin has low resistance to foreign substances, and if foreign substances remain in the pores, it will have a negative effect on the adhesiveness.

[0292] To solve the aforementioned problem, the inventors of the present invention conducted in-depth research on the influence of the relationship between pores present on the surface of the plating layer of a hot-formed part and the oxide layer formed on the surface of the plating layer, i.e., the outermost layer (d), on adhesive performance. As a result, they confirmed that adjusting the distribution of aluminum oxide according to the number of surface pores can improve adhesive performance, especially sealer adhesiveness, and therefore, the present invention has technical significance.

[0293] Accordingly, in a hot-formed member according to one embodiment of the present invention, the surface pores of the oxide layer present on the surface of the aluminum-based plating layer are 30 / 100㎛. 2 Exceeding ~80 / 100㎛ 2 Below, the distribution of aluminum oxide can be 90-100%. This means that even if the number of pores present on the surface of the oxide layer exceeds a certain amount per unit area, if the distribution of aluminum oxide increases, sealer adhesion can be secured.

[0294] The aforementioned types of adhesives include a coupling agent for adhesion to the surface to which they are applied, i.e., the surface of the plating layer. This coupling agent forms a covalent bond with the hydroxyl group of the oxide present on the surface of the plating layer. In view of this, a hot-formed member according to one embodiment of the present invention has surface pores of 30 / 100㎛ of the oxide layer present on the surface of the plating layer. 2 Exceeding ~80 / 100㎛ 2 Below, the distribution of aluminum oxide is suggested to be 90% or more. If 30 / 100㎛ are present on the surface of the oxide layer. 2 Exceeding ~80 / 100㎛ 2 When the distribution of aluminum oxide is less than 90% when pores are present, the coupling agent component of the adhesive does not have enough hydroxyl groups to form covalent bonds, preventing sufficient improvement in bond strength. Ultimately, the large number of pores causes a deterioration in bonding performance.

[0295] Here, the distribution of aluminum oxide may be 100%, which means that no Al metal is distributed on the surface of the plating layer. As will be described in detail below, as an example, when measuring the surface of the plating layer using XPS, no peak of Al metal may be observed.

[0296] Meanwhile, in the case where the number of pores present on the surface of the oxide layer present on the surface of the aluminum-based plating layer of the hot-formed member according to one embodiment of the present invention is smaller than the aforementioned case, the sealer adhesion at the target level can be secured even if the distribution of aluminum oxide is relatively low. Accordingly, in the hot-formed member according to one embodiment of the present invention, the number of surface pores of the oxide layer present on the surface of the plating layer is 30 / 100㎛. 2 When this is the case, the distribution of aluminum oxide is suggested to be 70% or more.

[0297] It is difficult to completely remove the pores present on the surface of the oxide layer, and rather, in order to suppress destruction due to hydrogen embrittlement, there are cases where pores are intentionally formed on the surface of the plating layer of a hot-formed part. Accordingly, regardless of the lower limit of the number of surface pores present on the surface of the oxide layer, 30 / 100㎛ 2 When the aluminum oxide distribution is less than 70%, the distribution of aluminum oxide described above can be applied. However, when the distribution of aluminum oxide on the surface of the oxide layer is less than 70%, the coupling agent in the adhesive as mentioned above will not have enough hydroxyl groups to bind, and thus, it will not be possible to improve the adhesive performance.

[0298] Here, the distribution of aluminum oxide can be obtained by measuring the surface of the plating layer of a hot-formed part in which an oxide layer exists.

[0299] As a non-limiting example, after analyzing the surface of the plating layer using XPS (X-ray Photoelectron Spectroscopy) equipment, which is effective in observing the surface structure of an object, the distribution of aluminum oxide can be measured from the relationship between aluminum oxide and aluminum metal present on the surface. Since the metal and the oxide of the metal have different binding energies (ev), peaks are generated at different locations during the XPS measurement.

[0300] Hereinafter, a more detailed explanation will be given with reference to the drawings.

[0301] First, Fig. 8 shows the results of measuring the surface of the plating layer of a hot-formed part according to an embodiment of the present invention using XPS. In this result graph, the metal content of elements, the oxide content, and the degree of their distribution can be confirmed from the position (x-axis, binding energy) and height (y-axis, intensity) where the peak occurs. In particular, in one embodiment of the present invention, the distribution of aluminum oxide can be calculated using the area under the peak representing aluminum metal and the area under the peak representing aluminum oxide. Specifically, the distribution of aluminum oxide is the ratio of the area under the aluminum oxide peak divided by [the area under the aluminum oxide peak + the area under the aluminum metal peak]. In this case, the area under the peak can be expressed as a value (area) obtained by multiplying the maximum height value (intensity value) of the corresponding peak and the value (binding energy) of the peak width at a point corresponding to the middle value (1 / 2 intensity value) of the maximum height. At this time, the value of the peak width is called FWHM, and the value of the base line is excluded when calculating the maximum height value of the peak.

[0302] For example, in the aluminum peak corresponding to 900℃ in Fig. 8, the lower area of ​​aluminum oxide is (96251Х2), and the lower area of ​​aluminum metal is (6616Х1.2), and the distribution of aluminum oxide calculated from this is 96.0%. In addition, it can be confirmed that the peak of aluminum metal does not appear in the aluminum peak corresponding to 930℃ in Fig. 8, which means that aluminum oxide exists at 100%.

[0303] In one embodiment of the present invention, the oxide layer mainly comprising aluminum oxide may have a thickness of 100 nm or less. If the thickness exceeds 100 nm, there is a risk that the plating layer may peel off due to excessive outflow of aluminum within the plating layer into the oxide. Meanwhile, there is no particular limitation on the lower limit of the thickness of the oxide layer, but in the case of a series of processes according to one embodiment of the present invention, the oxide layer may be formed to a thickness of approximately 30 nm or more.

[0304] Meanwhile, in one embodiment of the present invention, the base steel sheet may be any steel sheet capable of obtaining the plated steel sheet, when a plated steel sheet having an aluminum-based plating layer formed thereon is used as a steel sheet for hot forming. As an example, the base steel sheet may be carbon steel, and such carbon steel is widely known in the art, and thus there are no particular restrictions on the composition of alloying elements.

[0305] In particular, in one embodiment of the present invention, the alloy composition of the steel sheet may have the alloy composition of the steel sheet described above, and the description of each element is replaced with the aforementioned matters.

[0306] In addition, in one embodiment of the present invention, the aluminum-based plating layer is a plating layer containing aluminum (Al) as a main component, and the addition of elements other than Al is not excluded. As one example, elements other than Al may further include elements such as silicon (Si), magnesium (Mg), and zinc (Zn), and these elements may be included alone or in combination of two or more. A plating layer containing a mixture of these elements and Al may be referred to as an aluminum alloy plating layer.

[0307] A hot-formed member according to one embodiment of the present invention may include an Al-Si-based plating layer on at least one surface of a base steel sheet. In one embodiment of the present invention, the Al-Si-based plating layer may be composed of, in wt%, silicon (Si): 7.0 to 10.0%, iron (Fe): 5.0 to 15.0%, the remainder aluminum (Al), and other unavoidable impurities, but is not limited thereto. In this case, the content of each component in the plating layer refers to the plating layer composition of the plating steel sheet itself before hot-forming the aluminum-based plating steel sheet.

[0308] In one embodiment of the present invention, the aluminum-based plating layer can 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.

[0309] In one embodiment of the present invention, the silicon (Si) constituting the Al-Si-based plating layer suppresses excessive formation of an Al-Fe alloy phase generated by the reaction between Al in the plating bath and Fe of the base steel sheet during the plating process of the base steel sheet. To this end, the Al-Si-based plating layer may contain Si in an amount of 7% or more. However, if the content is excessive, exceeding 10%, the fluidity of the plating bath becomes excessively high, causing an increase in the plating bath temperature. In this case, a single structure of the Si eutectic phase (acid-like) that is not dissolved in Al may be formed, which may deteriorate the formability of the plated steel sheet. In addition, if the content of Si is less than 7%, there is a problem of reduced fluidity of the plating bath.

[0310] In one embodiment of the present invention, iron (Fe) contained in the plating layer may be introduced into the plating layer by Fe inevitably present in the plating bath, and may also be introduced into the plating layer by the dissolution of Fe from the base steel sheet during the plating process. The Fe introduced into the plating layer may form an alloy layer (b) as shown in Fig. 8, and this alloy layer serves to maintain adhesion between the plating layer and the base steel sheet. Due to this alloy layer, the hardness of the interface between the plating layer and the base steel sheet tends to be lower than that of the surface of the plating layer. If the content of Fe in the plating layer is less than 5%, the alloy layer may not be sufficiently formed, which may cause powdering, such as the plating layer being peeled off. On the other hand, if the content of Fe exceeds 15%, the plating layer becomes vulnerable to corrosion.

[0311] The components of the Al-Si plating layer, excluding Si and Fe, are Al and inevitable impurities. Al is a main component in obtaining an aluminum-plated steel sheet and is effective in improving the corrosion resistance of the plating steel sheet. Al may exist as a residual component in the Al-Si plating layer, but as an example, it may exist at 70 to 85%. As another example, the plating layer may contain 82% or less of Al.

[0312] During the manufacturing process of plated steel sheets with Al-Si plating, unavoidable impurities may be unintentionally introduced. It should be noted that the meaning of these unavoidable impurities will be readily understood by those skilled in the relevant field.

[0313] Meanwhile, the Al-Si-based plating layer according to one embodiment of the present invention may further include specific elements in addition to the aforementioned composition to improve the physical properties of the plating layer. As one example, the layer may further include one or more elements selected from the group consisting of the following:

[0314] i) One or more of chromium (Cr) and molybdenum (Mo): 2.5% or less

[0315] ii) One or more of niobium (Nb), zirconium (Zr), and vanadium (V): 0.1% or less

[0316] iii) Antimony (Sb): 0.02~0.03%

[0317] Among these, chromium (Cr) and molybdenum (Mo) can be added to improve the hardness of the plating layer, and if the content of at least one type exceeds 2.5%, the hardenability of the plating layer becomes excessively high, which may cause it to break easily. In addition, niobium (Nb), zirconium (Zr), and vanadium (V) can also be added to improve the hardness of the plating layer. Since these are expensive elements, the content of at least one type may be 0.1% or less for economic reasons. In addition, antimony (Sb) may be further included for the purpose of reducing hydrogen embrittlement of the plating layer, and to fully achieve the effect, it may be included in an amount of 0.02% or more. However, if the content exceeds 0.03%, excessive pores may be generated inside the plating layer, and these pores may further increase during high-temperature heating for hot forming, which may not only trap rust-preventive oil, but also cause excessive presence of dust and foreign substances in the plating layer.

[0318] Hereinafter, a method for manufacturing a hot-formed part according to one aspect of the present invention, specifically a method for manufacturing a hot-formed part with improved sealant adhesion, will be described in detail. However, it should be noted that the following manufacturing method is merely one example for manufacturing a hot-formed part.

[0319] In one embodiment of the present invention, a method for manufacturing a hot-formed part may include the steps of preparing a plated steel sheet having an aluminum-based plated layer on at least one surface of a base steel sheet; heating and maintaining the plated steel sheet at a high temperature; and forming and rapidly cooling the maintained plated steel sheet.

[0320] In one embodiment of the present invention, the base steel sheet for providing an aluminum-based plating layer on at least one surface may be any steel sheet capable of producing a plated steel sheet having an aluminum-based plating layer by plating treatment, and thus there is no particular limitation on its type. In addition, the content of the base steel sheet mentioned above may be replaced.

[0321] In one embodiment of the present invention, the aluminum-based plating layer may refer to, for example, an Al-Si-based plating layer. This Al-Si-based plating layer is a plating layer that contains aluminum (Al) as a main component, but also contains a certain amount of silicon. As an example, the Al-Si-based plating layer may be composed of, by weight %, silicon (Si): 7.0 to 10.0%, iron (Fe): 5.0 to 15.0%, the remainder aluminum (Al), and other unavoidable impurities. These compositions may be replaced with the description of the plating layer mentioned above.

[0322] Meanwhile, according to one embodiment of the present invention, the Al-Si plating layer may further include components other than the aforementioned components, and as one example, may further include one or more selected from the group consisting of the following. The description of the following elements may also be replaced with the preceding content.

[0323] i) One or more of chromium (Cr) and molybdenum (Mo): 2.5% or less

[0324] ii) One or more of niobium (Nb), zirconium (Zr), and vanadium (V): 0.1% or less

[0325] iii) Antimony (Sb): 0.02~0.03%

[0326] Meanwhile, a method for forming an aluminum-based plating layer, for example, an Al-Si-based plating layer, on at least one surface of a base steel sheet can utilize a hot-dip galvanizing process capable of obtaining a molten aluminum-plated steel sheet. As a non-limiting example, by immersing the base steel sheet in a hot-dip galvanizing bath containing Si, Fe, and Al in the aforementioned amounts, an Al-Si-based plating layer can be formed on both surfaces of the base steel sheet, and at this time, the Al-Si-based plating layer can be replaced with the content of the plating layer described above. In this way, an aluminum-plated steel sheet on which an Al-Si-based plating layer is formed on at least one surface of the base steel sheet can be referred to as an aluminum alloy-plated steel sheet.

[0327] In one embodiment of the present invention, hot forming can be performed on a plated steel sheet having an aluminum-based plated layer on at least one surface of the base steel sheet, and for this purpose, the plated steel sheet can be heated to a high temperature.

[0328] Coated steel sheets are mainly used as hot forming steel sheets for hot forming. When the coated steel sheet has an aluminum-based coating layer, during the high-temperature heating process for hot forming, iron (Fe) in the base steel sheet diffuses into the coating layer and reacts with aluminum (Al) within the coating layer to form an Fe-Al alloy phase. In addition, pores are created within the coating layer during the heating process.

[0329] As already mentioned, when a rust-preventive oil is applied to the surface of the plating layer of a hot-formed part, the rust-preventive oil is trapped in pores present on the surface of the plating layer, which acts as a factor that impairs the adhesive performance when applying an adhesive for the subsequent bonding process.

[0330] For this reason, the inventor of the present invention sought to induce Al to exist as an oxide rather than forming an alloy phase with Fe during the high-temperature heating of a plated steel sheet for hot forming. Accordingly, in one embodiment of the present invention, when heating a plated steel sheet to a target temperature for hot forming, conditions are provided for uniformly heating the surface of the plated layer of the plated steel sheet while simultaneously rapidly reaching the target temperature.

[0331] As a condition, according to one embodiment of the present invention, the plated steel sheet can be heated to a temperature range of 900 to 960°C at a heating rate of 15 to 20°C / s.

[0332] If the heating rate of the above-mentioned plated steel sheet is less than 15°C / s, the Al of the plated layer forms an alloy phase with the Fe diffused from the base steel sheet during the heating process, so that an oxide layer cannot be sufficiently formed on the surface of the plated layer. On the other hand, if the heating rate exceeds 20°C / s, the plated layer cannot be heated uniformly, and there is a concern that the surface may become uneven. In addition, if the heating temperature is less than 900°C when the above-mentioned plated steel sheet is heated, oxide may not be sufficiently formed on the surface of the plated layer, and on the other hand, if the temperature exceeds 960°C, there is a concern that the plated layer may melt.

[0333] Afterwards, a process of maintaining the heated galvanized steel sheet for a certain period of time can be performed. This process is intended to evenly distribute heat across the entire galvanized steel sheet, and can be performed for a minimum of 3 minutes and a maximum of 6 minutes.

[0334] If the holding time is less than 3 minutes, heat may not be evenly distributed across the entire steel sheet, potentially resulting in uneven shape during subsequent forming. Conversely, if the holding time exceeds 6 minutes, productivity declines, resulting in economic disadvantages. Furthermore, the intended oxide layer can only be formed within 6 minutes.

[0335] Once the above maintenance process is completed, the plated steel sheet can be formed and cooled at the same time, and the cooling can be performed by rapid cooling.

[0336] In one embodiment of the present invention, the heated and maintained plated steel sheet can be hot-formed into an intended shape using a mold or the like, and cooling (rapid cooling) can be performed simultaneously with the hot forming.

[0337] According to one embodiment of the present invention, the rapid cooling can prevent surface deviation according to the forming part by performing the rapid cooling at a cooling rate of 50°C / s or more. If the cooling rate during the rapid cooling is less than 50°C / s, time is given for the Fe diffused from the base steel sheet to react with Al, thereby preventing the formation of the intended oxide layer on the surface of the plating layer. In one embodiment of the present invention, the upper limit of the cooling rate during the rapid cooling is not particularly limited. However, in order to perform the cooling rate exceeding 1000°C / s, a separate cooling facility is required, and in this case, there is a problem of reduced economic feasibility.

[0338] Meanwhile, in performing the aforementioned cooling process, although not limited thereto, as one embodiment of the present invention, cooling may be terminated below Mf. If cooling is terminated at a temperature exceeding Mf, a process of cooling back to room temperature must be added, and in this case, it is difficult to ensure shape freezing of the hot-formed part. Here, Mf refers to the martensite transformation completion temperature.

[0339] By heating the plated steel sheet under the conditions described above, before the Al in the plated layer forms an alloy phase with Fe, an oxide layer can be advantageously formed on the surface of the plated layer by first reacting with moisture, oxygen, etc. in the air. This oxide layer mainly includes an aluminum oxide layer, and by forming a covalent bond with the coupling agent contained in the adhesive to the hydroxyl groups of this oxide, the adhesive strength can be effectively increased.

[0340] Hereinafter, a molding device according to a third aspect of the present invention and a molding method using the same will be described.

[0341] 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.

[0342] In one embodiment of the present invention, the high-strength steel material may be the aforementioned hot-forming steel plate and may have the aforementioned alloy composition. In addition, the material may be manufactured using the aforementioned manufacturing methods.

[0343] Figures 16 and 17 illustrate a molding apparatus according to one embodiment of the present invention. Specifically, Figure 16 illustrates an exploded perspective view of a molding apparatus according to one embodiment of the present invention, and Figure 17 illustrates a side view of a 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.

[0344] As shown in FIG. 16, a molding device according to one embodiment of the present invention includes a pad (B-200); a die (B-300) disposed outside the first direction (2) of the pad (B-200); and a punch (B-100) disposed below the pad (B-200) and including a body in which first to fifth punch forming portions (B-120, B-130, B-140, B-150, B-160) are formed. Although not shown in FIGS. 16 and 17, the molding device according to one embodiment of the present invention is a hot press forming device, and cooling channels (B-170, B-370; see FIG. 14) through which cooling water flows are disposed on the inside of the punch (B-100) and the die (B-300), so that the material can be hardened through heat treatment during or after molding.

[0345] The pad (B-200) and the die (B-300) are connected to the upper part of the press, and the punch (B-100) is connected to the lower part of the press, so that the material is formed while the pad (B-200) and the die (B-300) move in the third direction (4) that is the up-and-down direction toward the punch (B-100). Although not shown, the pad (B-200) and the die (B-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 (B-200), so that the pad (B-200) and the die (B-300) move together, and after the forming of the pad (B-200) is completed, a structure may be applied in which only the die (B-300) moves downward with respect to the pad (B-200) by the elastic member.

[0346] The punch (B-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 (B-100) includes, when viewed from the first direction (2), a first punch forming portion (B-110) that is linear, a second punch forming portion (B-120) that is curved and has a forming portion curvature radius (Rp) along a second direction (3) that is perpendicular to the first direction (2) on a horizontal plane, a third punch forming portion (B-130) that is linear, a fourth forming portion (B-140) that is curved and has the forming portion curvature radius (Rp), and a fifth punch forming portion (B-150) that is linear, and a support portion (B-160) that supports the material before forming is arranged on the outside of the first forming portion and the fifth forming portion (B-150).

[0347] The first and fifth punch forming parts (B-110, B-150) have a structure that is inclined toward the third punch forming part (B-130) as a whole, and the third punch forming part (B-130) has a structure that is parallel to a horizontal plane at the center, and the second and fourth punch forming parts (B-120, B-140) have a structure that connects the first and fifth punch forming parts (B-110, B-150) and the third punch forming part (B-130) by bending.

[0348] The first and second punch forming parts (B-110, B-120) and the fourth and fifth punch forming parts (B-140, B-150) have a symmetrical structure centered on the third punch forming part (B-130), and thus, one bracket is formed centered on the second punch forming part (B-120), and the other bracket is formed centered on the fourth punch forming part (B-140).

[0349] The first punch forming portion (B-110) includes a first extension surface forming portion (B-111) extending along the third direction (4) to form a flange (B-21, B-23; see FIG. 15) of a bracket (B-20; see FIG. 14) on both sides of the first direction (2), a first body forming portion (B-113) formed to form a body (B-23; see FIG. 15) of the bracket (B-20), and a first curved surface forming portion (B-112) having a bending radius of curvature (r) between the first extension surface forming portion (B-111) and the first body forming portion (B-113).

[0350] The second and third punch forming portions (B-120) and the third punch forming portions (B-130) also form the flanges (B-21, B-22) of the bracket (B-20) on both sides of the first direction (2), the second and third extension surface forming portions (B-121, B-131) extending along the third direction (4) to form the body (B-23) of the bracket (B-20), and the second and third body forming portions (B-123, B-133) arranged below the pad (B-200) and the second and third curved surfaces having the bending radius of curvature (r) between the second extension surface forming portion (B-121) and the second body forming portion (B-113) and between the third extension surface forming portion (B-131) and the third body forming portion (B-133) It includes a molding part (B-122, B-132). At this time, the third main body molding part (B-133) and the support part (B-160) can be parallel to the horizontal plane.

[0351] Since the fourth and fifth punch forming parts (B-140, B-150) have a structure symmetrical to the first and second punch forming parts (B-110, B-120), the fourth and fifth punch forming parts (B-140, B-150) also include the fourth and fifth extension surface forming parts (B-141, B-151), the fourth and fifth curved surface forming parts (B-142, B-152), and the fourth and fifth body forming parts (B-143).

[0352] Meanwhile, the pad (B-200) includes first to fifth pressing surfaces (B-210, B-220, B-230, B-240, B-250) having shapes corresponding to the first to fifth body forming portions (B-113, B-123, B-133, B-143) of the punch (B-100). The pad (B-200) presses the material toward the top of the punch (B-100) to primarily form the material to have an overall curved portion. The pad (B-200) may have a length from a length corresponding to the third body forming portion (B-133) in the first direction (2) to the third extension surface forming portion (B-131).

[0353] The die (B-300) is arranged on both sides of the first direction of the pad (B-200) and has a structure that forms flanges (B-21, B-22). In this embodiment, the die (B-300) is arranged on both sides to form the flanges (B-21, B-22) formed on both sides of the bracket (B-20), but is not limited thereto and may be arranged on only one side. Since the shapes of the two sides of the die (B-300) are symmetrical with respect to the pad (B-200), the description will be centered on one side of the die (B-300).

[0354] When viewed from the first direction (2), the die (B-300) includes a first die forming portion (B-310) having a straight shape, a second die forming portion (B-320) having a curved shape having a die curvature radius (Rd), a third die forming portion (B-330) having a straight shape, a fourth die forming portion (B-340) having a curved shape having the die curvature radius (Rd), and a fifth die forming portion (B-310) having a straight shape, corresponding to first to fifth forming portions (B-110, B-120, B-130, B-140, B-150) of the punch (B-100). The first to fifth die forming portions (B-310, B-320, B-330, B-340, B-350) are connected via a vertical plane (B-360).

[0355] Similar to the above punch (B-100), the first and second die forming sections (B-310, B-320) and the fourth and fifth die forming sections (B-340, B-350) in the die (B-300) have a structure that is symmetrical with respect to the third die forming section (B-330).

[0356] The first die forming portion (B-310) is adjacent to the punch (B-100) and includes a first die curved forming portion (B-311) formed into a curved surface at a position relatively close to the punch (B-100) in the first direction and a first flat forming portion (B-312) at a position relatively far from the punch (B-100).

[0357] Similarly, the second to fifth die forming sections (B-320, B-330, B-340, B-350) include second to fifth die curved forming sections (B-321, B-331, B-341, B-351) and second to fifth flat forming sections (B-322, B-332, B-342, B-352). The curved surfaces of the first to fifth die curved forming sections (B-311, B-321, B-331, B-341, B-351) increase in height as they get closer to the punch (B-100).

[0358] In this embodiment, the radius of curvature (Rd) in the second and fourth die forming portions (B-320, B-340) refers to the radius of curvature at the upper portion (B-321a, B-341a) closest to the punch (B-100) in the second and fourth curved forming portions (B-321, B-341) when viewed in the first direction (2).

[0359] As shown in Fig. 17, in this embodiment, the die (B-300) is configured so that when forming a flange, the first and fifth die forming sections (B-310, B-350) come into contact with the material first, the third die forming section (B-330) comes into contact with the material next, and the second and fourth die forming sections (B-320, B-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 (B-320, B-340) and the second and fourth punch forming sections (B-120, B-140) is secured so that stretching / contraction occurs, thereby preventing wrinkles or tears from occurring during the forming process.

[0360] Specifically, when the third body forming part (B-133) and the upper part (B-331a) of the third die forming part (B-330) are positioned (a) on the same plane, when viewed in the first direction (2), the first body forming part (B-113) is positioned (c) above the upper part (B-311a) of the first die forming part (B-310), and the second body forming part (B-123) is positioned (b) below the upper part (B-321a) of the second die forming part (B-320). The relationship between the symmetrical fourth and fifth die forming parts (B-340, B-350) and the fourth and fifth body forming parts (B-143, B-153) is also the same.

[0361] That is, when the third die forming section (B-330) starts flange forming the material, the first die forming section (B-310) is already performing flange forming, and the second die forming section (B-320), which is a curved section, is not yet performing forming.

[0362] In this embodiment, the length (lp) of the third body forming part (B-133) is longer than the length (ld) of the third die forming part (B-330), and the forming part curvature radius (Rp) of the second body forming part (B-123) is configured to be smaller than the die curvature radius (Rd) of the second die forming part (B-320), so that the above-described relationship can be achieved.

[0363] 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 (B-330). Accordingly, the centers of the die curvature radii (Rd) of the second die forming part (B-320) and the fourth die forming part (B-340) can be located at the same position, but are not limited thereto.

[0364] At this time, when viewed from the first direction, the angle (θ) at which the extension lines of the imaginary tangents of both ends intersect in the fourth punch forming section (B-143) may be 90° or more, and specifically, may be between 95 and 135°, and of course, the same applies to the second punch forming section (B-123).

[0365] 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.

[0366] 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 the radius of curvature in the battery case is 3 mm, whether forming is possible or not is determined depending on the radius of curvature (Rp) of the forming portion. This will be explained again when explaining the bracket for the battery case.

[0367] FIGS. 18 to 24 illustrate a molding method according to an embodiment of the present invention, wherein FIG. 18 is a flowchart of a molding method according to an embodiment of the present invention, FIG. 19 is a plan view of a material input into a molding device according to an embodiment of the present invention, FIG. 20 is a schematic perspective view showing a first molding step in a molding method according to an embodiment of the present invention, and FIGS. 21, 22a, and 22b are 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, and FIG. 23 is a front view showing a cooling step in a molding method according to an embodiment of the present invention, and FIG. 24 is a perspective view showing a trimming step in a molding method according to an embodiment of the present invention.

[0368] 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. 16.

[0369] A forming method according to one embodiment of the present invention comprises: a material placing step (S110) of placing a heated material (B-400) on a punch (B-100) having a forming portion and having a length longer in a first direction (2) than the punch (B-100); a first forming step (S120) of forming the material (B-400) into the shape of a main body forming portion (B-113, B-123, B-133, B-143) of the punch (B-100) through a pad (B-200) positioned above the punch (B-100); a second forming step (S130) of forming the material (B-400) to follow the shape of the forming portion of the punch (B-100) through a die (B-300) positioned outside the pad (B-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.

[0370] The material settling step (S110) is a step of feeding the material into a forming device and settling it on a punch (B-100). At this time, the material is a steel plate, and the material is settling on the punch (B-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.

[0371] In one embodiment of the present invention, the material may be the hot forming steel sheet described above and may have the alloy composition described above.

[0372] In addition, in order to form two brackets at a time in the present invention, the material (B-400) includes notches (B-410) formed on both sides toward the center of the material in the second direction (3). The notches (B-410) cause deformation to be concentrated during forming, thereby preventing cracks from occurring in areas other than the notches (B-410).

[0373] As shown in Fig. 20, the first forming step (S120) is a step of forming the material (B-400) into a curve through the pad (B-200) after the material (B-400) is settled, and the material (B-400) is formed by pressing the material (B-400) with the pad (B-200) from above the punch (B-100).

[0374] As shown in FIGS. 21 to 22a and 22b, the secondary forming step (S130) is a step of forming a flange on a curved material through a die (B-300), which is a step of deforming the material by applying pressure to the die (B-300) on a portion of the material (B-400) that is not in contact with the pad (B-200) that is formed primarily by the pad (B-200). At this time, as described in FIG. 17, in the secondary forming step (S130), the die (B-300) forms the edge portion, the center portion, and the middle portion between the center and the edge of the material in that order in the second direction (3), so that the curved portion of the primarily formed material (B-400), i.e., the second and fourth punch forming portions (B-120, B-140), can be formed last, thereby forming a flange on the material (B-400). At this time, the shape of the forming part of the punch (B-100) and die (B-300) is described through Figs. 16 and 17.

[0375] The cooling step (S140) is a step of cooling the material (B-400) during or after forming, and cools the material (B-400) having an austenite structure by circulating a cooling fluid through a cooling channel (B-170, B-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 (B-400) a high-strength steel having a tensile strength of 1200 MPa or more. In this embodiment, the cooling channels (B-170, B-370) are formed in both the punch (B-100) and the die (B-300). If the austenite structure can be transformed into a martensite structure, the cooling channels (B-170, B-370) may be provided in only one of them, and if necessary, the cooling channels (B-170, B-370) may also be provided in the pad (B-200).

[0376] After the cooling step (S140) is completed, a trimming step (S150) is performed to cut the formed material (B-400) along the cutting line (B-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 (B-120, B-140) of the punch (B-100).

[0377] 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.

[0378] FIG. 25 shows a perspective view of a bracket manufactured using a molding method according to one embodiment of the present invention.

[0379] The bracket (B-20) of Fig. 25 has a main body (B-23) and flanges (B-21, B-22), and is curved overall with a curvature radius (Rp) of the molded portion. At this time, the flanges (B-21, B-22) are connected to the main body (B-23) by a curved surface (B-24) that is curved with a curvature radius (r). The surface of the main body (B-23), the flanges (B-21, B-22) of the bracket (B-20), and the curved surface (B-24) therebetween that is formed with the curvature radius (Rp) of the molded portion can be called a molded surface.

[0380] FIG. 26 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. 27 shows a thickness reduction rate distribution diagram of comparative example 1-1 manufactured by another molding method, and FIG. 28 shows a thickness reduction rate distribution graph in a cross section of the molded products of FIGS. 26 and 27.

[0381] The thickness reduction rate distribution diagram is a diagram showing how the thickness of the material (B-400, see Figure 19) changes after molding. The thickness reduction rate is obtained by subtracting the thickness of the bracket (B-20) at the corresponding location from the initial thickness (tini) of the material (B-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.

[0382] The embodiment of Fig. 26 was manufactured using the molding device of Fig. 16, and a material heated to have a martensite structure of 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's curvature radius of curvature (Rp) was 22 mm.

[0383] As shown in Figs. 26 and 28, since the thickness of the main body (B-23) in the bracket (B-20) is not different from the initial thickness (tini), the average thickness (tav) of the main body (B-23) of the bracket (B-20) can be regarded as the initial thickness (tini) of the material (B-400), and the value obtained by subtracting the thickness of each position from the average thickness (tav) of the main body (B-23) and dividing it by the average thickness (tav) can be regarded as the thickness reduction rate.

[0384] Comparative Example 1-1 is a product formed by supplying 1500 MPa mart steel as a material through the same forming device.

[0385] As shown in Fig. 28, when manufacturing a bracket using the molding device and molding method according to one embodiment of the present invention (embodiment 1-1), 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 (B-21, B-22), which may deteriorate the sealing performance when manufacturing the battery case.

[0386] In addition, as shown in Fig. 28, 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.

[0387] However, in the case of Comparative Example 1-1, a thickness reduction rate of -0.8 occurs at the maximum thickness (tmax) position, indicating buckling in that area. Such buckling not only leads to cracks that compromise the structural performance of the battery case, but also potentially allows water to enter that area, making brackets like Comparative Example 1-1 inapplicable to battery cases. To maintain sealing properties, it is advantageous to maintain a thickness reduction rate of -0.4 or higher even in the curved area.

[0388] 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, if the curvature radius (r) of the molded part is less than 3 mm, it is 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. Even if flange molding is possible because the curvature radius (r) of the molded part is 3 mm, molding was not properly performed at the flange of the curved part when the curvature radius (Rp) of the molded part was less than 22 mm. Meanwhile, if the curvature radius (r) of the molded part and the curvature radius (Rp) of the molded part increased, there was no difficulty in molding itself, but there was a problem that the curvature radius of the battery case increased, creating a dead space, which made it impractical. Therefore, it is preferable that the sum of the curvature radius (Rp) of the molded part and the curvature radius (r) of the bending part be 30 mm or less for a bracket applicable to a battery case.

[0389] In addition, in the bracket (B-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 a dead space where the battery cells, which are roughly rectangular in shape, are not filled, making it impractical.

[0390] Meanwhile, Fig. 29 shows a side view showing the molding method of Comparative Example 1-2, and Fig. 30 shows a perspective view of a molded product manufactured using the molding method of Comparative Example 1-2.

[0391] The molding method of Fig. 29 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 (B-300) is formed so that the center has the lowest upper position (B-301a), and the molding is performed sequentially toward the outside.

[0392] Even if the hot press forming process is applied in the same way in this case, as shown in Fig. 30, a folding area (B) is created, and a bracket that cannot be used as a battery case is produced.

[0393] 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.

[0394] Hereinafter, a hot press-formed part according to the fourth aspect of the present invention will be described.

[0395] FIG. 31 illustrates a perspective view of a molded part according to one embodiment of the present invention, and FIG. 32 illustrates a front view of a molded part according to one embodiment of the present invention.

[0396] A hot press-formed part according to one embodiment of the present invention includes a first wall (C-110) extending in a first direction (Y direction) and a second wall (C-120) extending in a direction intersecting the first wall (C-110), a curvature (C-160) is formed between the first wall (C-110) and the second wall (C-120), an angle between an arbitrary line perpendicular to the first direction (a line parallel to the Z direction) and the second wall (C-120) is 0° or more and 5° or less, and the first wall (C-110), the second wall (C-120) and the curvature (C-160) are formed integrally.

[0397] A hot press-formed part according to one embodiment of the present invention includes a first wall (C-110), a second wall (C-120), and a curved portion (C-160) positioned between the first wall (C-110) and the second wall (C-120). The first wall (C-110), the curved portion (C-160), and the second wall (C-120) are integrally formed in that order.

[0398] A hot press-formed part has the characteristic of being formed as a single body, including a first wall (C-110) formed parallel to a first direction, a curved portion (C-160) curved from the first wall (C-110), and a second wall (C-120) connected to one end of the curved portion (C-160).

[0399] Assuming an arbitrary line perpendicular to the first direction, the second wall (C-120) may have an angle of 0° or more and 5° or less with the arbitrary line.

[0400] 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.

[0401] 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.

[0402] One embodiment of the present invention relates to a molded part (C-10) formed as an integral part including a first wall (C-110), a curved portion (C-160), and a second wall (C-120) through a hot press forming method, wherein the second wall (C-120) has an angle of 0° to 5° with respect to the arbitrary line, which is smaller than a conventional angle. Accordingly, the first wall (C-110) and the second wall (C-120) have a shape close to a right angle, so that the space surrounded by the first wall (C-110) and the second wall (C-120) can be efficiently used.

[0403] According to one embodiment of the present invention, the first wall (C-110), the second wall (C-120) and the curved portion (C-160) can be formed integrally by processing a plate material.

[0404] The first wall (C-110), the curved portion (C-160), and the second wall (C-120) can be formed as a single body using a blank formed by joining a single body or multiple bodies in the thickness direction using a hot press forming method. Since the blank is formed as a single body using a hot press, processing is convenient, and processing problems or breakage due to stress concentration at joints such as welds can be prevented, while a molded part (C-10) having a relatively high tensile strength can be manufactured.

[0405] In one embodiment of the present invention, the plate may be the hot forming steel plate described above and may have the alloy composition described above.

[0406] According to one embodiment of the present invention, the radius of curvature (r) of the curved portion (C-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.

[0407] 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 (C-10).

[0408] 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 (C-130) and the fourth wall (C-140) are parallel to the first direction, and the fifth wall (C-150) is connected to the third wall (C-130) and the fourth wall (C-140), and the third wall (C-130) extends from the second wall (C-120), and the first wall (C-110) to the fifth wall (C-150) can be formed integrally.

[0409] According to the hot press forming process, a hat-shaped shape with multiple walls can be formed at once, resulting in excellent formability.

[0410] For example, a third wall (C-130) and a fourth wall (C-140) may be formed parallel to the first direction, and the first wall (C-110) and the fourth wall (C-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 (C-130) may have a different height. The fifth wall may be positioned between the third wall (C-130) and the fourth wall (C-140), the second wall (C-120) and the third wall (C-130) may be connected by a first connecting portion (C-170), the third wall (C-130) and the fifth wall (C-150) may be connected by a second connecting portion (C-180), and the fifth wall (C-150) and the fourth wall (C-140) may be connected by a third connecting portion (C-190). Accordingly, the first to fifth walls (C-150), the curved portion (C-160), and the first connecting portion (C-170) to the third connecting portion (C-190) may be integrally formed by processing a plate material.

[0411] Here, the first connecting portion (C-170) to the third connecting portion (C-190) can be formed into a shape having a curvature radius like the curved portion (C-160), and at this time, the curvature radius may have all the characteristics of the curved portion (C-160) of the first wall (C-110) and the second wall (C-120). However, it is not limited to this shape.

[0412] According to one embodiment of the present invention, the tensile strength of the molded part may be 1300 to 2100 MPa.

[0413] 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.

[0414] 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.

[0415] In addition, the microstructure forming the molded part (C-10) may be composed of martensite with an area fraction of 98% or more. The molded part (C-10) according to the present invention may form a tensile strength of the ultra-high strength level as described above by having martensite, a hard phase with high strength, occupying most of the area fraction.

[0416] 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.

[0417] According to one embodiment of the present invention, when a third wall (C-130) is further included that is parallel to the first direction and connected to the second wall (C-120), and a length in a direction perpendicular to the first direction from the first wall (C-110) to the third wall (C-130) is defined as a wall height (hw), and an angle between an arbitrary line perpendicular to the first direction and the second wall (C-120) is defined as a wall angle (θw), the following [Relational Expression 3] can be satisfied.

[0418] [Relationship 3]

[0419] hw ≤ 13.4 * θw + 182.4

[0420] Here, the unit of hw is mm, the unit of θw is degree, and the left and right sides are nondimensionalized and calculated.

[0421] A molded part processed by hot press forming that satisfies the above [Relationship 3] can be manufactured with excellent quality without defects such as cracks.

[0422] Referring to Table 1 below, it can be seen that formability is excellent when the above formula is satisfied.

[0423] Division θw (°) hw (mm) Calculated value of the right side [Relationship 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

[0424] 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.

[0425] Fig. 33a is a drawing interpreted in the same manner as the conditions of Invention Example 2-1, and Fig. 33b is a drawing interpreted in the same manner as the conditions of Comparative Example 2-1. Comparing Figs. 33a and 33b, it can be seen that in Comparative Example 2-1, a crack occurs in the upper part of the second wall (C-120) or the fifth wall (C-150), indicated in red, and some parts are interpreted as parts at risk of crack occurrence, indicated in yellow.

[0426] Fig. 34a is a drawing interpreted in the same manner as the conditions of Invention Example 2-3, and Fig. 34b is a drawing interpreted in the conditions of Comparative Example 2-3. Comparing Figs. 34a and 34b, it can be seen that in Comparative Example 2-3, a crack, indicated in red, occurs in the lower part of the second wall (C-120) or the fifth wall (C-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.

[0427] Hereinafter, another aspect of the present invention, a battery pack module, will be described.

[0428] The battery pack module below includes the molded part described above, and the description of the molded part is cited above.

[0429] FIG. 35 is a drawing illustrating a battery pack module according to one embodiment of the present invention, and FIG. 36 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).

[0430] A battery pack module (C-1) according to one embodiment of the present invention includes a battery case (C-20) formed to surround a battery pack, a base (C-30) positioned at a lower portion of the battery case (C-20) and connected to the battery case (C-20) to form a space in which the battery pack is positioned, and a hot press-molded part (C-10) positioned across the interior of the battery case (C-20) and connected to the battery case (C-20) and the base (C-30).

[0431] The battery case (C-20) is formed to surround the side of the battery pack, and the base (C-30) is formed of a general plate or has a curve or groove as needed, and is configured to place the battery pack.

[0432] For example, a reinforcing member (C-40) may be further included to be bonded to the outer surface of the battery case (C-20) to prevent collision.

[0433] For example, a hot press-formed part (C-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 (C-20).

[0434] For example, the hot press-formed parts (C-10) may be arranged in multiple numbers at regular intervals within the battery case (C-20).

[0435] The battery pack is positioned in the space formed between the base (C-30), the battery case (C-20), and the cross member, and the battery pack module (C-1) is intended to stably position the battery in the vehicle body, including the battery pack.

[0436] 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 (C-1) itself, thereby preventing fires caused by damage to the battery due to impact.

[0437] In addition, since a plurality of cross members are generally provided within the battery case (C-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 (C-1) has the same volume, it provides the effect of increasing the battery capacity.

[0438] 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 (C-10b) of embodiment 2-2 of FIG. 36 (b) is formed to be larger than the radius of curvature r1 of the lower end of the hot press-formed part (C-10a) of embodiment 2-1 of FIG. 36 (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. 36 (b) is formed to be larger than the gap g1 of FIG. 36 (a), and as the radius of curvature (r) increases, the space that cannot be used for mounting the battery pack (b) becomes larger.

[0439] 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 (C-1).

[0440] Hereinafter, a hot press-formed part according to the fifth aspect of the present invention will be described.

[0441] Fig. 37 is a perspective view illustrating a press-molded part according to one embodiment of the present invention. Fig. 38 is a perspective view illustrating a press-molded part according to another embodiment of the present invention. Fig. 39 (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. 39 (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. 40 (a) is an example showing a strain applied to a press-molded part manufactured using a conventional manufacturing method, and Fig. 40 (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.

[0442] Referring to FIGS. 37 and 38, press-formed parts (D-10, D-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 (D-10, D-10').

[0443] The press-formed part (D-10, D-10') may include a flat portion (D-110) that is not press-formed and thus has a flat shape, and a deformed portion (D-120) that is a portion that is convex in one direction due to press-forming. At this time, a plurality of deformed portions (D-120) may be formed. In this case, the flat portions (D-110) may be arranged between a plurality of deformed portions (D-120).

[0444] The deformation portion (D-120) may have a convex shape protruding upward (+Z) based on the drawing. At this time, the deformation portion (D-120) may include a top plate portion (D-121), a longitudinal wall portion (D-122), and a boundary portion (D-123).

[0445] The top plate (D-121) may be the upper end of a deformation portion (D-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 (D-10, D-10').

[0446] The longitudinal wall portion (D-122) may be a side wall portion of a deformation portion (D-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 (D-120).

[0447] The longitudinal wall portion (D-122) may be continuous with the top plate portion (D-121). More specifically, the longitudinal wall portion (D-122) may be arranged so that its upper end is continuous with one side end of the top plate portion (D-121). A pair of such longitudinal wall portions (D-122) may be provided. A pair of longitudinal wall portions (D-122) may be arranged so as to be continuous with each of the two side ends of the top plate portion (D-121), thereby forming two side wall portions of the deformation portion (D-120).

[0448] The portion (hereinafter, shoulder portion) (D-121a) where the side end of the top plate portion (D-121) and the upper end of the longitudinal wall portion (D-122) are connected may have a round shape having a first radius of curvature. In this case, the shoulder portion (D-121a) may be convexly curved toward the outside of the deformation portion (D-120).

[0449] The boundary portion (D-123) may be a boundary between a deformation portion (D-120) and a flat portion (D-110) that are continuous along the longitudinal direction (Y) of the press-molded part (D-10, D-10'). One end of the boundary portion (D-123) may be continuous with the lower end of the longitudinal wall portion (D-122), and the other end of the boundary portion (D-123) may be continuous with one end of the flat portion (D-110). At this time, the other end of the flat portion (D-110) may be continuous with a boundary portion (D-123) provided in another deformation portion (D-120). A pair of such boundary portions (D-123) may be provided, and arranged to be continuous with each of the lower ends of the pair of longitudinal wall portions (D-122).

[0450] The boundary portion (D-123) may be rounded with a second radius of curvature. The boundary portion (D-123) may be concavely curved inwardly of the deformation portion (D-120). In this case, the second radius of curvature may be the same as or similar to the first radius of curvature.

[0451] As described above, the deformation portion (D-120) may have a shape in which a boundary portion (D-123), a longitudinal wall portion (D-122), a top plate portion (D-121), a longitudinal wall portion (D-122), and a boundary portion (D-123) are sequentially connected along the longitudinal direction (Y). Accordingly, the deformation portion (D-120) may have a shape like a hat or a similar shape.

[0452] As described above, a plurality of deformation sections (D-120) may be provided. More specifically, at least three deformation sections (D-120) may be provided. In this case, a flat section (D-110) may be arranged between two adjacent deformation sections (D-120) among the plurality of deformation sections (D-120). In this case, the two adjacent deformation sections (D-120) may be connected by the flat section (D-110) located at the center thereof.

[0453] Accordingly, the press-formed part (D-10, D-10') may have a form in which three or more deformed parts (D-120) and a plurality of flat parts (D-110) are arranged alternately in a row along the longitudinal direction (Y). At this time, the flat parts (D-110) may be arranged on both outer sides of the press-formed part (D-10, D-10') based on the longitudinal direction (Y), but the present invention is not limited thereto.

[0454] The deformation portion (D-120) can be formed with a preset height (h). At this time, the preset height (h) is the height of the deformation portion (D-120), and may mean the length from the lower surface of the flat portion (D-110) to the upper surface of the top plate portion (D-121).

[0455] Two adjacent deformation sections (D-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 (D-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 (D-110) positioned between the two adjacent deformation sections (D-120).

[0456] As illustrated in FIG. 37, a press-formed part (D-10) according to one embodiment of the present invention (hereinafter, Embodiment 3-1) may include three deformed portions (D-120). Accordingly, the press-formed part (D-10) of Embodiment 3-1 may include at least two flat portions (D-110) so as to be arranged between the three deformed portions (D-120).

[0457] As illustrated in FIG. 38, a press-formed part (D-10') according to another embodiment of the present invention (hereinafter, Embodiment 3-2) may include four or more deformed portions (D-120). Accordingly, the press-formed part (D-10) of Embodiment 1 may include at least three flat portions (D-110) so as to be arranged between the four or more deformed portions (D-120).

[0458] Meanwhile, although the drawing only illustrates a case where the press-formed part (D-10') has four deformation sections (D-120), the present invention is not limited thereto. Although not illustrated in the drawing, as another example, the press-formed part (D-10') may have five or more deformation sections (D-120), and in this case, the upper limit of the number of deformation sections (D-120) is not limited.

[0459] Referring to FIGS. 39 and 40, in the case of the conventional hot press forming method, the deformation portion (D-120) is first formed, and then a separate flat metal plate is bonded to the lower end of the formed deformation portion (D-120). In this case, as the number of deformation portions (D-120) to be formed increases, as exemplarily illustrated in (a) of FIG. 40, the force (deformation force) (stress) is concentrated on the vertical wall portion (D-122) to which the flat metal plates are connected and its surrounding area [A1 and B1 of FIG. 40 (a)] during the manufacturing process. As a result, there is a disadvantage in that cracks, etc. occur in the deformation portion (D-120) of the press-formed part, causing damage. To prevent this, the distance between the connected deformation parts (D-120) must be increased, but since the size of the press-formed part (D-10, D-10') to be manufactured is inevitably limited, there is a problem that the number of deformation parts (D-120) that can be included in it is also limited.

[0460] Accordingly, in one embodiment of the present invention, a press-formed part (D-10, D-10') capable of preventing damage to a deformation part (D-120) due to hot press forming is provided by utilizing the relationship between the height (preset height) (h) of a deformation part (D-120) and the distance (preset length) (w) between two adjacent deformation parts (D-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 (D-120) formed in the press-formed part (D-10, D-10').

[0461] In the case of the press-formed part (D-10) according to embodiment 3-1 of the present invention, since three deformation parts (D-120) are formed, the relationship between the “preset height (h)” of the deformation parts (D-120) and the “preset length (w)” of the distance between two adjacent deformation parts (D-120) can be defined by the following [Relational Expression 4].

[0462] w min≤w≤114.85e 0.0455h ... [Relationship 4]

[0463] 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.

[0464] As shown in the graph of Fig. 39 (a) and Fig. 40 (b), when three deformation sections (D-120) included in a press-formed part (D-10) are designed so that the distance (predetermined length) (w) apart from each other satisfies [Relationship 4], the occurrence of damage such as cracks in the deformation sections (D-120) and their surroundings [A2 and B2 in Fig. 40 (b)] during the hot press forming process can be minimized. At this time, the manufacturing method of the press-formed part (D-10) according to embodiment 3-1 will be described in detail below.

[0465] In addition, in the case of the press-formed part (D-10) according to embodiment 3-2 of the present invention, since four or more deformation parts (D-120) are formed, the relationship between the “preset height (h)” of the deformation parts (D-120) and the “preset length (w)” of the distance between two adjacent deformation parts (D-120) can be defined by the following [Relational Expression 5].

[0466] w min ≤w≤46.309e 0.105h ... [Relationship 5]

[0467] 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.

[0468] As shown in the graph of Fig. 39 (b) and Fig. 40 (b), when three deformation sections (D-120) included in a press-formed part (D-10) are designed so that the distance (predetermined length) (w) apart from each other satisfies [Relationship 5], the occurrence of damage such as cracks in the deformation sections (D-120) and their surroundings [A2 and B2 in Fig. 40 (b)] can be minimized during the hot press forming process. At this time, the manufacturing method of the press-formed part (D-10) according to embodiment 3-1 will be described in detail below.

[0469] Meanwhile, in the above-described embodiments 3-1 and 3-2, the preset length (w) may be 20 mm or more. That is, the minimum distance (w) between two adjacent deformation parts (D-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 (D-210) provided in the molds (D-200, D-400) and / or between the second pressurizing parts (D-410) and the intermediate pressurizing parts (D-300) in the manufacturing device (D-20, D-20') of the press-molded parts (D-10, D-10') to be described later.

[0470] FIG. 41 is a flowchart illustrating a method for manufacturing a press-formed part according to one embodiment of the present invention. FIG. 42 schematically illustrates a first step for manufacturing the press-formed part of FIG. 37. FIG. 43 schematically illustrates a second step for manufacturing the press-formed part of FIG. 37. FIG. 44 schematically illustrates a third step for manufacturing the press-formed part of FIG. 37. And FIG. 45 schematically illustrates a fourth step for manufacturing the press-formed part of FIG. 37.

[0471] Referring to FIGS. 41 to 45, a manufacturing device (D-20) for manufacturing a press-molded part (D-10) according to embodiment 3-1 may include a first mold (D-200), an intermediate pressurizing part (D-300), and a second mold (D-400). In this case, one intermediate pressurizing part (D-300) may be provided. At this time, based on the vertical direction (Z), the first mold (D-200) may be an upper mold, and the second mold (D-400) may be a lower mold.

[0472] The first mold (D-200) and the second mold (D-400) may be arranged to face each other along the pressing direction (-Z). The first mold (D-200) may be arranged above the second mold (D-400). At this time, the first mold (D-200) may be installed on an upper support (not shown) that can be elevated. Accordingly, the first mold (D-200) may be lowered toward the second mold (D-400) or elevated away from the second mold (D-400). In addition, the second mold (D-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 (D-20) is installed, for example.

[0473] The first mold (D-200) may be provided with a first pressurizing portion (D-210). The first pressurizing portion (D-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 (D-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 (D-210) may be configured to have a shape and size corresponding to the "upper surface of the deformed portion (D-120) of the press-formed part (D-10)" described above.

[0474] The manufacturing device (D-20) is for manufacturing the press-molded part (D-10) of embodiment 3-1, and may be provided with three first pressurizing parts (D-210). At this time, the three first pressurizing parts (D-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 (D-200) may be provided with a first flat part (D-220). The first flat part (D-220) may be arranged between two adjacent first pressurizing parts (D-210). The first flat part (D-220) may extend parallel to the longitudinal direction (Y) between the two first pressurizing parts (D-210), thereby connecting the first pressurizing parts (D-210). As described above, since three first pressurized portions (D-210) are provided, at least two first flat portions (D-220) may be provided.

[0475] Accordingly, the first mold (D-200) may be formed such that three first pressurizing portions (D-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 (D-220) is arranged between them to connect the first pressurizing portions (D-210).

[0476] The second mold (D-400) may be provided with a second pressurizing portion (D-410) and a second flat portion (D-420a). At this time, the second pressurizing portion (D-410) may be formed in a shape and size corresponding to the lower surface of the press-molded part (D-10).

[0477] Unlike the first mold (D-200), the second mold (D-400) may be provided with only two second pressurizing portions (D-410). In this case, the two second pressurizing portions (D-410) may be arranged symmetrically with the two first pressurizing portions (D-210) located on both sides among the three first pressurizing portions (D-210) along the longitudinal direction (Y). Accordingly, in the second mold (D-400), the second pressurizing portion (D-410) may not exist in the area (hereinafter, the center area) facing the first pressurizing portion (D-210) located in the middle among the three first pressurizing portions (D-210).

[0478] Accordingly, the second mold (D-400) may be a single structure having a form connected by two second pressurizing portions (D-410) and a second flat portion (D-420a) disposed therebetween. At this time, the flat portion (D-420a) may be provided with a penetrating portion (D-420aa). When press forming the outer region of the metal plate (D-10A), an intermediate pressurizing portion (D-300) may be inserted into the penetrating portion (D-420aa). The penetrating portion (D-420aa) may be formed by penetrating a portion of the flat portion (D-420a) along the vertical direction (Z). This penetrating portion (D-420aa) may have a cross-sectional shape and an area corresponding to the shape and size of the intermediate pressurizing portion (D-300). Additionally, a second-second flat portion (D-420b) may be further provided on each side of the first pressurized portions (D-210).

[0479] The intermediate pressurizing portion (D-300) may be placed between the first mold (D-200) and the second mold (D-400). As illustrated in Fig. 42, the metal plate (D-10A), which is a press-molding target, may be placed on the lower side of the first mold (D-200). In this case, the intermediate pressurizing portion (D-300) is positioned between the metal plate (D-10A) and the second mold (D-400), and may pressurize a portion of the lower surface of the metal plate (D-10A) when the first mold (D-200) is lowered. The intermediate pressurizing portion (D-300) may be, for example, a pad for pressing and bending the lower surface of the metal plate (D-10A).

[0480] The intermediate pressurizing portion (D-300) may be positioned directly above the above-described central region of the second mold (D-400). At this time, the intermediate pressurizing portion (D-300) may have the same shape as the second pressurizing portion (D-410). That is, the intermediate pressurizing portion (D-300) may have a shape and size corresponding to the lower surface of the press-molded part (D-10). During press molding, the intermediate pressurizing portion (D-300), together with the middle first pressurizing portion (D-210) among the three first pressurizing portions (D-210), may pressurize the metal plate (D-10A) upward and downward to form the deformation portion (D-120) located in the center.

[0481] The intermediate pressurizing section (D-300) may be configured to be elevable. Accordingly, the intermediate pressurizing section (D-300) can descend along the pressing direction (-Z) during press forming. In addition, the intermediate pressurizing section (D-300) can rise in the opposite direction (Z) to the pressing direction after press forming is completed. This elevation of the intermediate pressurizing section (D-300) can be realized by an elastic member (not shown) installed in the intermediate pressurizing section (D-300).

[0482] The “manufacturing method of a press-molded part (D-10) according to embodiment 3-1” using the above manufacturing device (D-20) may be as follows.

[0483] First, a metal plate (D-10A) can be supplied to a manufacturing device (D-20) (S100). Before press forming begins, as illustrated in Fig. 42, the metal plate (D-10A) can be placed at a position (hereinafter referred to as a processing position) between the first mold (D-200) and the intermediate pressurizing portion (D-300). Meanwhile, the metal plate (D-10A) can be supplied to the manufacturing device (D-20) while being heated by a separate heating device (not illustrated).

[0484] For example, when the metal plate (D-10A) is the processing position, the upper surface of the metal plate (D-10A) may be positioned so that it contacts the lower surface of the first mold (D-200) or there is only a slight gap therebetween. At this time, the second mold (D-400) may be positioned symmetrically with the first mold (D-200), with the metal plate (D-10A) and the intermediate pressurizing portion (D-300) interposed therebetween.

[0485] In addition, when the metal plate (D-10A) is placed at the processing position (i.e., before press forming begins), the intermediate pressurizing portion (D-300) may be placed on the upper side of the second mold (D-400). Accordingly, a height difference (hi) may exist between the intermediate pressurizing portion (D-300) and the second pressurizing portion (D-410). Here, the height difference (hi) may mean the distance from the upper surface of the second pressurizing portion (D-410) to the upper surface of the intermediate pressurizing portion (D-300). In this case, the height difference (hi) between the intermediate pressurizing portion (D-300) and the second pressurizing portion (D-410) may be smaller than the “preset height (h)”, which is the height of the press-formed part (D-10). At this time, the height difference (hi) may be 65% or more of the preset height (h). When the manufacturing device (D-20) is configured to have such a height difference (hi), damage such as cracks in the deformed portion (D-120) formed through press forming can be minimized.

[0486] Next, the metal plate (D-10A) can be first press-formed by the first mold (D-200) and the intermediate pressurizing portion (D-300) (S200). As illustrated in Fig. 43, the first mold (D-200) can be lowered along the pressing direction (-Z) to pressurize the upper surface of the metal plate (D-10A). In this case, the first mold (D-200) can be lowered to a position where the lower surface of the metal plate (D-10A) does not come into contact with the second mold (D-400). At this time, since the intermediate pressurizing portion (D-300) is positioned higher than the second pressurizing portion (D-410) by the height difference (hi), only the intermediate pressurizing portion (D-300) is introduced into the first pressurizing portion (D-210) and can pressurize the center region of the metal plate (D-10A). Accordingly, only the central region of the metal plate (D-10A) can be pressed in the vertical direction by the central first pressing portion (D-210) among the three first pressing portions (D-210) and the intermediate pressing portion (D-300). Accordingly, only the central region of the metal plate (D-10A) can be bent, thereby forming one deformed portion (D-120).

[0487] Next, the metal plate (D-10A) can be secondarily press-formed by the first mold (D-200) and the second mold (D-400) (S300). After the first press-formed is performed in step S200, the first mold (D-200) can be further lowered along the pressing direction (-Z), as illustrated in FIG. 44. In this process, the intermediate pressing portion (D-300) can be lowered together with the first mold (D-200) while being inserted into the central first pressing portion (D-210) together with the central region of the metal plate (D-10A). Accordingly, the outer region of the metal plate (D-10A) can come into contact with the upper surfaces of the two second pressing portions (D-410).

[0488] Thereafter, as the first mold (D-200) continues to descend, the second pressurizing portion (D-410) is introduced into the first pressurizing portion (D-210) and can pressurize both outer regions of the metal plate (D-10A). In this process, the intermediate pressurizing portion (D-300) can be accommodated into the through portion (D-420aa) of the second mold (D-400). Both outer regions of the metal plate (D-10A) can be simultaneously pressed in the vertical direction by the two outer first pressurizing portions (D-210) and the two outer second pressurizing portions (D-410). As a result, both outer regions of the metal plate (D-10A) are bent, so that two additional deformed regions (D-120) can be formed.

[0489] Next, the first mold (D-200) and the intermediate pressurizing portion (D-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. 45, the first mold (D-200) can be raised in the opposite direction (+Z) to the pressing direction (-Z). In this process, the deformation portions (D-120) can be separated from the first pressure portions (D-210). In addition, the intermediate pressurizing portion (D-300) can be separated from the central deformation portion (D-120) and returned to its original position. As a result, a press-formed part (D-10) having three deformation portions (D-120) having a preset height (h) and spaced apart from each other by a preset length (w) can be manufactured.

[0490] Then, the press-formed part (D-10) that has been manufactured can be discharged (S500). After being discharged from the manufacturing device (D-20), the press-formed part (D-10) can be transported for the next processing or manufacturing process. Thereafter, the next metal plate (D-10A) is supplied, so that the aforementioned manufacturing method can be repeatedly performed.

[0491] Fig. 46 schematically illustrates the first step of manufacturing the press-formed part of Fig. 38. Fig. 47 schematically illustrates the second step of manufacturing the press-formed part of Fig. 38. Fig. 48 schematically illustrates the third step of manufacturing the press-formed part of Fig. 38. And Fig. 49 schematically illustrates the fourth step of manufacturing the press-formed part of Fig. 38.

[0492] Referring to FIG. 41 and FIG. 46 to FIG. 49, a press-molded part (D-10) according to embodiment 3-2 can be manufactured through the following manufacturing method. A manufacturing device (D-20') for a press-molded part can include a first mold (D-200), an intermediate pressurizing part (D-300), and a second mold (D-400). At this time, at least two intermediate pressurizing parts (D-300) can be provided. In this case, most of the features of the first mold (D-200), the intermediate pressurizing part (D-300), and the second mold (D-400) are the same or similar to those of the aforementioned embodiment 3-1, and therefore, a duplicate description thereof will be omitted.

[0493] Since the press-molded part (D-10') according to embodiment 3-2 is provided with four or more deformation sections (D-120), the first mold (D-200) may be provided with four or more first pressurizing sections (D-210). For convenience of explanation, the following description will focus on a case where four first pressurizing sections (D-210) are provided and are spaced apart from each other by a preset length (w). In this case, two first pressurizing sections (D-210) may be arranged in the center area of ​​the first mold (D-200), and one first pressurizing section (D-210) may be arranged on each side of the center.

[0494] The second mold (D-400) may be provided with two second pressurizing parts (D-410). At this time, the two second pressurizing parts (D-410) may be arranged to face the two first pressurizing parts (D-210) arranged on each side of the first mold (D-200).

[0495] When four first pressurizing parts (D-210) are provided, two intermediate pressurizing parts (D-300) may be provided. In this case, the two intermediate pressurizing parts (D-300) may be arranged to face the two first pressurizing parts (D-210) arranged in the center area of ​​the first mold (D-200). As in the case described above, the intermediate pressurizing parts (D-300) are arranged between the first mold (D-200) and the second mold (D-400).

[0496] In addition, in the case of embodiment 3-2, the second flat portion (D-420a) of the second mold (D-400) may be provided with two through-hole portions (D-420aa). Accordingly, when the outer region of the metal plate (D-10A) is press-formed by the first mold (D-200) and the second mold (D-400), the two intermediate pressurizing portions (D-300) can be accommodated in the through-hole portions (D-420aa), respectively.

[0497] In the case of the "method for manufacturing a press-molded part (D-10') according to Embodiment 3-2" using the above-described manufacturing device (D-20'), steps S100, S200, S300, and S400 can be sequentially performed, similarly to the method for manufacturing the press-molded part (D-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.

[0498] First, in step S100, as illustrated in FIG. 46, the metal plate (D-10') may be supplied to the aforementioned processing position. In this case, the metal plate (D-10A) may be supplied to the manufacturing device (D-20') in a heated state by a separate heating device (not illustrated). When supplied to the processing position, two intermediate pressurizing portions (D-300) may be positioned below the center region of the metal plate (D-10'). At this time, the two intermediate pressurizing portions (D-300) may be arranged at the same height. In this case, the height difference (hi) between the intermediate pressurizing portions (D-300) and the second pressurizing portions (D-410) is the same as in embodiment 3-1.

[0499] Next, in step S200, as illustrated in FIG. 47, as the first mold (D-200) is lowered, the intermediate pressurizing portions (D-300) are each introduced into the two first pressurizing portions (D-210) arranged in the central region of the first mold (D-200), and the central region of the metal plate (D-10') can be pressed. By this first press forming step, two deformation portions (D-120) can be formed in the central region of the metal plate (D-10A).

[0500] Next, in step S300, as illustrated in FIG. 48, the first mold (D-200) may be lowered further, and the second pressurizing portions (D-410) may be introduced into the two first pressurizing portions (D-210) arranged in the outer region of the first mold (D-200), respectively. Accordingly, the outer region of the metal plate (D-10') may be pressed in the vertical direction by the first pressurizing portions (D-210) and the second pressurizing portions (D-410). By this second press forming step, two deformation portions (D-120) may be additionally formed in the outer region of the metal plate (D-10A).

[0501] Next, in step S400, as illustrated in FIG. 49, the first mold (D-200) can be raised in the opposite direction (+Z) to the pressing direction (-Z). Accordingly, the press-formed part (D-10') in a press-formed state can be separated from the first mold (D-200), the intermediate pressurizing part (D-300), and the second mold (D-400). In this process, the two intermediate pressurizing parts (D-300) can be raised and returned to their original positions at the processing positions described above.

[0502] Then, after the manufactured press-formed part (D-10') is discharged from the manufacturing device (D-20'), the next press-formed process can begin as a new metal plate (D-10') is supplied.

[0503] Meanwhile, when the number of deformed parts (D-120) formed in the press-molded part (D-10') increases, the number of intermediate pressurized parts (D-300) may also increase accordingly.

[0504] For example, although not shown in the drawing, if five deformation portions (D-120) are formed in a press-molded part (D-10'), the first mold (D-200) must be provided with five first pressurizing portions (D-210). Accordingly, three intermediate pressurizing portions (D-300) may be provided, and may be arranged to face the three first pressurizing portions (D-210) arranged in the center area of ​​the first mold (D-200). In this case, the three intermediate pressurizing portions (D-300) may be arranged between the first mold (D-200) and the second mold (D-400).

[0505] Among the three intermediate pressurizing parts (D-300), one intermediate pressurizing part (hereinafter, the first intermediate pressurizing part) (D-300) arranged in the middle may be arranged at the highest position. The remaining two intermediate pressurizing parts (hereinafter, the second intermediate pressurizing parts) (D-300) may be arranged between the first intermediate pressurizing part (D-300) and the second mold (D-400). At this time, the two second intermediate pressurizing parts (D-300) may be arranged at the same height. The height difference between the first intermediate pressurizing part (D-300) and the second intermediate pressurizing part (D-300) may be the same as or similar to the height difference (hi) between the aforementioned intermediate pressurizing part (D-300) and the second pressurizing part (D-410).

[0506] In this arranged state, first press forming can be performed by the first mold (D-200) and the first intermediate press portion (D-300). When the first press forming is completed or immediately before completion, the first mold (D-200) is lowered further together with the first intermediate press portion (D-300), so that second press forming can be performed by the first mold (D-200) and the two second intermediate press portions (D-300). By these two press formings, forming of the center region of the metal plate (D-10A) can be performed first. Thereafter, after the second press forming is completed or immediately before completion, the first mold (D-200) is lowered further, so that third press forming of the outer region of the metal plate (D-10A) can be performed by the first mold (D-200) and the second mold (D-400).

[0507] As another example, although not shown in the drawing, if six deformation portions (D-120) are formed in the press-molded part (D-10'), the first mold (D-200) must be provided with six first pressurizing portions (D-210). Accordingly, four intermediate pressurizing portions (D-300) may be provided, and may be arranged to face the four first pressurizing portions (D-210) arranged in the center area of ​​the first mold (D-200). In this case, the four intermediate pressurizing portions (D-300) may be arranged between the first mold (D-200) and the second mold (D-400).

[0508] Among the four intermediate pressurizing parts (D-300), the two intermediate pressurizing parts (hereinafter, first intermediate pressurizing parts) (D-300) arranged in the middle may be arranged at the highest position. The remaining two intermediate pressurizing parts (hereinafter, second intermediate pressurizing parts) (D-300) may be arranged between the first intermediate pressurizing part (D-300) and the second mold (D-400). At this time, the two first intermediate pressurizing parts (D-300) may be arranged at the same height. And, the two second intermediate pressurizing parts (D-300) may also be arranged at the same height. The height difference between the first intermediate pressurizing part (D-300) and the second intermediate pressurizing part (D-300) may be the same as or similar to the height difference (hi) between the aforementioned intermediate pressurizing part (D-300) and the second pressurizing part (D-410).

[0509] In this arrangement, first press forming can be performed by the first mold (D-200) and two first intermediate press portions (D-300). When the first press forming is completed, or immediately before completion, the first mold (D-200) is lowered further together with the first intermediate press portions (D-300), so that second press forming can be performed by the first mold (D-200) and two second intermediate press portions (D-300). By these two press formings, forming of the central region of the metal plate (D-10A) can be performed first. Thereafter, after the second press forming is completed or just before completion, the first mold (D-200) is lowered further, whereby the third press forming can be performed on the outer area of ​​the metal plate (D-10A) by the first mold (D-200) and the second mold (D-400).

[0510] In addition, when the number of deformation sections (D-120) formed in the press-molded part (D-10') increases to 7 or more, the number of first press sections (D-210) and intermediate press sections (D-300) must be further increased similarly to the above. Accordingly, the number of penetration sections (D-420aa) in the second mold (D-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 (D-10A), and then press-molding can be performed on the outer region of the metal plate (D-10A).

[0511] The press-formed parts (D-10, D-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 (D-10, D-10') by arranging an intermediate press portion (D-300) having a height difference (hi) between upper / lower molds (D-200, D-400) and using three press portions (D-210, D-300, D-410). At this time, through a step-by-step forming process of first pressing the center region of the metal plate (D-10, D-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 (D-10, D-10') during press working. As a result, the press-formed parts (D-10, D-10') can be prevented from being damaged during the manufacturing process, and the quality of the parts can be improved.

[0512] 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.

[0513] [Explanation of symbols]

[0514] B-1: Side Frame B-10: Frame

[0515] B-20: Bracket B-21, B-22: Flange

[0516] B-23: Body B-24: Curved surface

[0517] B-100: Punch

[0518] B-110, B-120, B-130, B-140, B-150: 1st to 5th punch forming sections

[0519] B-111, B-121, B-131, B-141, B-151: First to fifth extension surface forming parts

[0520] B-112, B-122, B-132, B-142, B-152: First to fifth curved forming sections

[0521] B-113, B-123, B-133, B-143: First to fourth main body molding parts

[0522] B-200: Pad

[0523] B-300: Die

[0524] B-310, B-320, B-330, B-340, B-350: 1st to 5th die forming sections

[0525] B-311, B-321, B-331, B-341, B-351: 1st to 5th die curved forming sections

[0526] B-312, B-322, B-332, B-342, B-352: 1st to 5th die flat forming sections

[0527] B-360: Vertical plane

[0528] B-400: Material B-410: Notch

[0529] C-1: Battery pack module C-10: Hot press molded part

[0530] C-20: Battery Case C-30: Base

[0531] C-40: Reinforcing member C-110: First wall

[0532] C-120: Second wall C-130: Third wall

[0533] C-140: 4th wall C-150: 5th wall

[0534] C-160: Curved section C-170: First connecting section

[0535] C-180: Second connection C-190: Third connection

[0536] b: battery pack r: radius of curvature

[0537] t: plate thickness θw: wall angle

[0538] hw: wall height

[0539] D-10, D-10': Press-formed parts

[0540] D-10A: Metal plate

[0541] D-110: Reputation Department

[0542] D-120: Transformation section

[0543] D-20, D-20': Press forming device

[0544] D-200: Mold 1

[0545] D-210: First projection

[0546] D-220: First plane section

[0547] D-300: Intermediate pressurization section

[0548] D-400: Second mold

[0549] D-410: Second protrusion

[0550] D-420: Second plane

[0551] Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are intended only to illustrate and further illustrate the present invention 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.

[0552] (Example 1)

[0553] Steel slabs having an alloy composition shown in Table 2 below and a thickness of 80 mm were manufactured through vacuum melting. Each steel slab was heated to 1250°C, then final hot-rolled at 900°C, cooled at a cooling rate of 30°C / s, and coiled at 600°C to obtain a hot-rolled steel sheet with a final thickness of 3.0 mm. Thereafter, each of the hot-rolled steel sheets was pickled and then cold-rolled at a cold reduction ratio of 50% to manufacture a cold-rolled steel sheet. Thereafter, the cold-rolled steel sheet was annealed at an annealing temperature of 780°C in a 5% hydrogen-95% nitrogen atmosphere, and then cooled to manufacture annealed cold-rolled steel sheets.

[0554] Using the above cold rolled steel sheet, one side is coated with 75 g / m of Al plating bath containing 9% Si by weight. 2 Double-sided plating was performed with the plating amount, and an aluminum-based plated steel sheet manufactured according to the above conditions was made into a blank, and then the blank was transferred into a heating furnace, and heat treatment conditions according to the conditions shown in Table 3 below were applied using a hot forming mold, and hot forming and cooling were performed to obtain a hot-formed part. At this time, the cooling rate during the cooling was 20 to 200°C / s.

[0555] The required heat treatment time threshold (Ttotal) was calculated by applying the calculated Ae3 temperature and heating condition values ​​to Equation 2, and whether Equation 2 was satisfied is shown in Table 3.

[0556] In addition, in order to confirm whether the plating layer of each hot-formed member was alloyed, the microstructure of the aluminum-based alloy plating layer was evaluated by observing it with an optical microscope (OM) and a scanning electron microscope (SEM), and the alloying was determined and shown in Table 3 below.

[0557] For fully alloyed parts among the hot-formed parts manufactured through Table 3, the Cr content of the intermediate layer and the outermost layer within the aluminum alloy plating layer was evaluated through GDOES (Glow Discharge Optical Emission Spectrometry), and the maximum Cr value (Crmax) of each layer was measured, and the Cr increase / decrease rate (%) according to this was indicated in Table 4 below.

[0558] In order to evaluate the paint corrosion resistance of the obtained hot-formed part, a diagonal scribe with a size of w 0.5 x L 100 was formed on the part subjected to electrodeposition painting, and 63 cycles were applied while the CCT conditions were exposed under the following corrosive atmosphere, and the left / right widths of the diagonal scribe of the corroded paint blister were measured and added together.

[0559] CCT cycle: Salt spray application (35 degrees, 3 hours) -> drying (60 degrees, 2 hours) -> moistening (50 degrees, 95% relative humidity, 3 hours)

[0560] Steel grade CSiMnPSAlCrTiBSbA0.3450.331.10.010.0030.040.240.0270.00250.094B0.0920.270.70.010.0010.030.200.0220.00250.053C0.3150.411.20.010.0020.040.230.0250.00250.022D0.2070.301.90.010.0030.030.210.0170.00250.014E0.2210.251.30.010.0020.030.180.0300.00250.003

[0561] Classification Steel grade Sb content Ae3 Heating furnace condition [Relationship 1] T total Critical relationship 1 Satisfaction status 100% alloying of plating layer T furnace (℃)T total(sec) Invention example A-1A0.094807.9915300158.6OO Invention example A-2A0.094807.9900270166.2OO Comparative example A-1A0.094807.9885180184.3XX Invention example A-3B0.053871.3930240206.6OO Invention example A-4B0.053871.3900270243.3OO Comparative example A-2B0.053871.3885300385.6XX Invention example A-5C0.022817.1920210161.7OO Invention example A-6C0.022817.1900270178.5OO Comparative example A-3C0.022817.1890180188.8XXComparison Example A-4D0.014826.7900270188.3OOComparison Example A-5E0.003833.3900270196.0OO

[0562] As shown in Table 3, Comparative Examples A-1 to A-3, which did not satisfy Equation 2 during heating for hot forming, did not completely alloy the aluminum-based plating layer. Figures 1 to 3 are SEM photographs of the hot-formed members of Invention Examples A-3 and A-4 and Comparative Example A-2. Looking at these, it can be confirmed that in the case of Comparative Example A-2, the aluminum-based plating layer was not completely alloyed compared to Invention Examples A-3 and A-4.

[0563] For this reason, in the case of the comparative examples A-1 to A-3, the electrodeposition coating was not sufficiently prepared during the preparation of the electrodeposition coating for the corrosion resistance evaluation, so the coating corrosion resistance evaluation was not possible.

[0564] ClassificationSb content (wt.%)Cr content (wt.%) and increase rateCoating corrosion resistance (sum of left / right blister width, mm)Maximum value in the outermost layer (A)Maximum value in the middle layer (B){(AB)*100} / B (%)Invention example A-10.0940.1620.11146.02.1Invention example A-20.0940.1480.11726.52.9Invention example A-30.0530.1600.13023.13.6Invention example A-40.0530.1580.13120.63.9Invention example A-50.0220.1400.1316.84.8Invention example A-60.0220.1360.1277.14.5Comparative example A-40.0140.1070.138-22.55.9 Comparative example A-50.0030.1120.159-29.66.6

[0565] In the case of Comparative Examples A-4 and A-5, where the Sb content is below the range proposed in the present invention, it can be confirmed that the Crmax value in the middle layer is significantly higher than the Crmax value in the outermost layer, and thus the corrosion resistance is significantly reduced after the electrodeposition coating evaluation.

[0566] On the other hand, in invention examples A-1 to A-6, in which Sb was sufficiently added to the steel, the Cr increase / decrease rate (%) value derived by equation 1 was 5% or more, and thus, as a result of conducting a corrosion resistance evaluation after electrodeposition painting, it was confirmed that the corrosion blister width was significantly reduced.

[0567] The following Figures 4 and 5 are photographs of corroded painted blisters after the paint corrosion resistance evaluation of Invention Example A-6 and Comparative Example A-4, respectively. Inspection thereof shows that in the case of Invention Example A-6, the left-right widths of the corroded painted blisters after the paint corrosion resistance evaluation are 2.1 mm and 2.4 mm, respectively, and the total is only 4.5 mm, whereas in the case of Comparative Example A-4, the total left-right widths of the corroded painted blisters after the same paint corrosion resistance evaluation are 5.9 mm. Thus, it can be confirmed that the hot-formed member of Invention Example A-6 was able to secure excellent corrosion resistance by controlling the Cr increase / decrease rate (%) between the outermost layer and the middle layer.

[0568] In addition, FIGS. 6 and 7 are graphs showing the GDS observation results of Invention Example A-6 and Comparative Example A-4. Looking at the drawings, it can be seen that, compared to Invention Example A-6, Comparative Example A-4 has a higher Cr content in the middle layer than in the outermost layer. As a result, Comparative Example A-4 locally exhibited reduced corrosion resistance, and the corresponding area acted as a corrosion site, accelerating corrosion.

[0569] (Example 2)

[0570] Example 2-1. Analysis of the number of pores and aluminum oxide distribution in the plating layer of a hot-formed part.

[0571] A plated steel sheet was prepared in which the aluminum-based plating layer was composed of Si: 8.5% by weight, Fe: 10%, the remainder Al, and unavoidable impurities. Thereafter, the plated steel sheet was heated and maintained at a high temperature under the conditions shown in Table 5 below, and then cooled along with forming to manufacture a hot-formed part.

[0572] The surface of each hot-formed part manufactured in this way was measured by XPS to derive the Al oxide distribution. In addition, the number of pores present on the surface of each hot-formed part was observed. At this time, 20 randomly selected areas on the surface of the plating layer were then 10×10㎛ each. 2 The number of pores within the area was measured and the average value was calculated and displayed.

[0573] Steel grade heat treatment conditions Surface characteristics of plating layer Heating rate (℃ / s) Heating temperature (℃) Holding time (min) Cooling rate (℃ / s) Al oxide distribution (%) A Comparative example B-114.587066074.3 BI invention example B-115.090066096.0 C invention example B-215.5930660100 A Comparative example B-28.096056057.2 BI invention example B-316.0960560100

[0574] As shown in Table 5 and Fig. 10, it can be confirmed that as the heat treatment (heating) temperature for hot press forming increases, the number of pores present on the surface of the plating layer after hot forming increases.

[0575] Fig. 9 shows photographs of the surface and thickness-direction cross-section of the plating layer of Comparative Example B-1 and Inventive Examples B-1 and B-2 observed by SEM, and Fig. 10 shows the results of measuring the number of pores present on the surface of each plating layer per unit area. The area corresponding to '×' in Fig. 10 is the average value.

[0576] As shown in Fig. 9, it can be confirmed that as the heat treatment temperature increases, pores on the surface of the plating layer increase, which can also be confirmed from the results of Fig. 10. In addition, the tendency of pores to increase is similar to the cross-section of the plating layer, and it can be seen that the size of the pores also gradually increases.

[0577] In particular, fine cracks in a checkerboard pattern occur on the surface of the plating layer, and these cracks may be connected to pores existing inside the plating layer, so it may be easy for anti-rust oil or moisture to enter.

[0578] Meanwhile, these results were also identical / similar in Comparative Example B-2 and Invention Example B-3, which were not shown separately.

[0579] Figure 11 shows the results of measuring the surfaces of Comparative Example B-1 and Invention Examples B-1 and B-2 using XPS.

[0580] As shown in Fig. 11, it can be confirmed that peaks of aluminum oxide and metal are measured. Using the values ​​of intensity and bonding energy of each peak, the distribution of Al oxide on the surface was calculated, and the values ​​are as shown in Table 5.

[0581] In addition, for comparative example B-2 and invention example B-3, which were not shown separately, the Al oxide distribution was calculated after XPS measurement and shown together in Table 5.

[0582] Example 2-2. Evaluation of adhesive strength of hot-formed parts

[0583] After producing specimens from the hot-formed parts corresponding to Comparative Example B-1 of Example 2-1 and Inventive Examples B-1 and B-2, the surface of each specimen was cleaned with isopropanol, and then rust preventive oil was applied. At this time, as shown in Fig. 12, four specimens were prepared and rust preventive oil was applied in amounts of 10 uL, 20 uL, 50 uL, and 100 uL, respectively. For comparison, specimens without rust preventive oil were also prepared.

[0584] After applying the above-mentioned anti-rust oil, the surface condition after 24 hours of curing was checked, and the results are shown in Fig. 12. As can be seen in Fig. 12, the gloss tends to decrease as the number of pores on the surface increases, and for example, it can be seen that the gloss of Inventive Example B-2 decreases compared to Comparative Example B-1.

[0585] For the specimens to which a certain amount of anti-rust oil was applied as described above, an adhesive (mastic sealer) was applied over the anti-rust oil, and then cured at 155°C for 15 minutes. At this time, the curing temperature was set based on the minimum curing temperature of the adhesive used, and since it corresponds to the minimum temperature at which the adhesive exhibits adhesive properties, discrimination can be secured based on this standard.

[0586] Adhesion was then evaluated through shear tensile testing. Specifically, tensile testing was performed at a rate of 10 mm / min. Spacers were used to prevent stress loss, taking into account the difference between the thickness of the adhesive applied and the thickness of the specimen. The evaluation criteria were based on the automotive industry's standard of 0.2 MPa.

[0587] The results are shown in Figure 13.

[0588] First, as shown in (a) of Fig. 13, as the amount of applied anti-rust oil increases, the adhesive strength of the adhesive tends to decrease. In addition, as the number of pores increases, the adhesive strength tends to decrease, but it can be confirmed that the adhesive strength of Invention Example B-2, which has a high distribution of Al oxide on the surface, is higher than that of Invention Example B-1. This is evaluated to be due to maximizing direct contact between the Al oxide present on the surface of the plating layer and the adhesive.

[0589] Furthermore, Fig. 14 (b) is a result of observing the surface of each specimen to which adhesive has been applied, and it can be visually confirmed that the amount of adhesive remaining on the surface is greater in Invention Example B-2 than in Comparative Example B-1 even though the amount of anti-rust oil applied is increased.

[0590] In conclusion, even if a large number of pores exist on the surface of the plating layer of a hot-formed part, if the surface is mainly composed of aluminum oxide, the bonding strength is not reduced and the bonding property is maintained. In addition, when manufacturing a hot-formed part, the heating time to the target temperature can be reduced, which not only provides economic benefits such as improved productivity, but also provides environmentally friendly effects by reducing CO2 emissions generated during the parts manufacturing process. Therefore, the present invention has remarkable technical advantages.

Claims

1. Sojigang; Contains an aluminum alloy plating layer, The above steel contains Sb in an amount of 0.015 to 0.10% by weight. The above aluminum alloy plating layer includes an intermediate layer and an outermost layer located above the intermediate layer, A hot-formed member having a Cr increase / decrease rate (%) derived from the following relational expression 1 of 5% or more. [Relationship 1] (In the above relational expression 1, A means Crmax of the outermost layer, and B means Crmax of the intermediate layer.) 2. In paragraph 1, The above-mentioned steel is a hot-formed member comprising, in weight%, C: 0.080 to 0.50%, Si: 0.050 to 1.0%, Mn: 0.50 to 4.0%, P: 0.0150% or less (excluding 0%), S: 0.0200% or less (excluding 0%), Al: 0.010 to 0.10%, N: 0.02000% or less (excluding 0%), and Cr: 0.01 to 1%, with the remainder being Fe and unavoidable impurities.

3. In paragraph 1, A hot-formed member, wherein the above-mentioned steel further contains at least one element selected from the following a) to f). a) At least one selected from titanium (Ti), niobium (Nb), zirconium (Zr) and vanadium (V): 0.005 to 0.400 wt%, b) Boron (B): 0.0001 to 0.0100 wt%, c) At least one of molybdenum (Mo) and tungsten (W): 0.001 to 1.000 wt%, d) At least one of copper (Cu) and nickel (Ni): 0.003 to 2,000 wt%, e) One or more types of tin (Sn): 0.001 to 1.000 wt% f) Rare earth elements (REM): 0.0200 wt% or less 4. In paragraph 1, A hot-formed member having Simax of the intermediate layer of 5.5% to 15% in weight%.

5. In paragraph 1, A hot-formed member that satisfies the requirement that the total width of the left and right corrosion blisters after electroplating and coating corrosion resistance evaluation is 5.0 mm or less.

6. A step for preparing a base steel containing 0.015 to 0.10% Sb by weight; A step of immersing the above-mentioned steel in an aluminum-based plating bath to obtain an aluminum-based plated steel; A step of heating and maintaining the above aluminum-based plating steel to a temperature of Ae3 or higher to obtain an aluminum-based alloy plating steel; and It includes a step of cooling the above aluminum-based alloy plated steel after hot forming, A method for manufacturing a hot-formed member satisfying the following relational expression 2. [Relationship 2] (In the above relational expression 2, t total is the total heating time (sec) in the furnace during the above heating, Ae3 is the equilibrium temperature (℃) at which transformation to austenite is completed, and T furnace refers to the set temperature (℃) inside the furnace during the above heating.) 7. In paragraph 1, A method for manufacturing a hot-formed member, wherein the above-mentioned steel contains, in wt%, C: 0.080 to 0.50%, Si: 0.050 to 1.0%, Mn: 0.50 to 4.0%, P: 0.0150% or less (excluding 0%), S: 0.0200% or less (excluding 0%), Al: 0.010 to 0.10%, N: 0.02000% or less (excluding 0%), and Cr: 0.01 to 1%, with the remainder being Fe and unavoidable impurities.

8. In paragraph 1, A method for manufacturing a hot-formed member, wherein the above-mentioned steel further contains at least one element selected from the following a) to f). a) At least one selected from titanium (Ti), niobium (Nb), zirconium (Zr) and vanadium (V): 0.005 to 0.400 wt%, b) Boron (B): 0.0001 to 0.0100 wt%, c) At least one of molybdenum (Mo) and tungsten (W): 0.001 to 1.000 wt%, d) At least one of copper (Cu) and nickel (Ni): 0.003 to 2,000 wt%, e) One or more types of tin (Sn): 0.001 to 1.000 wt% f) Rare earth elements (REM): 0.0200 wt% or less 9. In paragraph 1, A method for manufacturing a hot-formed member, wherein the cooling speed in the above cooling step is 10 to 1000°C / s.

Images