Aluminized steel sheet, thermal-molded component using same, and method for producing same

Abstract

The present invention relates to an aluminized steel sheet for automobiles and the like, a hot-formed member manufactured using the aluminized steel sheet, and methods for manufacturing the aluminized steel sheet and the hot-formed member.

Description

Technical Field

[0001] The present invention relates to an aluminum-plated steel sheet used for automobiles and the like, a hot-formed component produced using the aluminum-plated steel sheet, and methods thereof. Background Art

[0002] In recent years, fuel efficiency has been improved by reducing the weight of automobiles. To achieve this, the thickness of steel can be reduced, but reducing the thickness may cause problems with automobile stability, so the strength of steel must be increased as a support. For this reason, the demand for high-strength steel is growing, and various types of steel have been developed. However, this steel has high strength, so there are problems with poor workability such as springback.

[0003] In order to solve this problem, a hot forming process has been proposed. The hot forming process is also called hot press forming, hot working, etc. The hot forming process is a method in which steel is processed at a high temperature suitable for processing (above 800°C), then stamped in a mold, and quickly cooled to a low temperature, thereby forming a low-temperature structure such as martensite in the steel, thereby improving the strength of the final product. In the case as described above, the problem of processability can be minimized when manufacturing parts with high strength.

[0004] When such hot forming is used, not only can complex shapes be easily formed, but also the manufactured parts (hot-formed parts) have the advantage of ensuring high strength, so its usability has been increasing in recent years. In particular, by using plated steel using aluminum, zinc, etc. on the surface of the steel, high corrosion resistance can also be ensured. As an example, Patent Document 1 discloses the use of aluminum-plated steel sheets in hot forming processes.

[0005] When a steel material plated with aluminum, zinc, etc. is heated for hot forming, Fe in the base iron diffuses into the plated layer and reacts with the plated layer of aluminum, zinc, etc. to form an alloy. In this case, the plated layer becomes brittle and alloy layer powder may be generated on the surface. This alloy layer powder continues to accumulate in the die during stamping processing in the die, eventually causing the problem of die adhesion (die pollution).

[0006] When the alloy layer powder is stacked on the mold and causes metal adhesion, an indentation is generated on the hot-formed part formed in the mold. The indentation caused by mold adhesion is different from the surrounding part. The thickness of the steel material is relatively thin, and when it is applied to a car body that requires high strength, it is subjected to stress concentration and causes a problem that it may be easily damaged. This problem is directly related to the safety when applied to automobiles, so it is necessary to eliminate this problem.

[0007] The mold sticking phenomenon is unavoidable for automobile parts manufacturers, so automobile parts manufacturers confirm the state of the mold and use an air blower to blow off and remove the alloy layer powder stacked on the mold before mold sticking occurs, or when mold sticking occurs, stop the hot forming production line and remove it with a grinder or the like.

[0008] The problems and inconveniences caused by the mold sticking as described above have the problem of lowering the quality and productivity of products, and thus there is a growing demand for improvement of the situation.

[0009] (Patent Document 1) U.S. Patent No. 6296805 Summary of the invention

[0010] 1. Technical issues to be resolved

[0011] One aspect of the present invention relates to an aluminum-plated steel sheet that can be used for hot forming or the like, an aluminum-plated steel sheet having excellent anti-die sticking properties, a hot-formed component using the aluminum-plated steel sheet, and methods for producing the same.

[0012] The technical problems of the present invention are not limited to the above contents. Those skilled in the art in the technical field to which the present invention belongs can easily understand the additional technical problems of the present invention based on the full text of the specification of the present invention.

[0013] (II) Technical solution

[0014] One embodiment of the present invention relates to an aluminum-plated steel plate, which includes a base steel plate and an Al-plated layer formed on the base steel plate. From the GDOES analysis results of the surface of the Al-plated layer along the thickness direction, the Fe concentration gradient in the range of 40-90 wt % in the Al-plated layer is 13-26 wt % / μm, and the Fe content of the Al-plated layer is 8-24 wt %.

[0015] The Al-plated layer may include an alloy layer formed at an interface between the Al-plated layer and the base steel plate, and the thickness of the alloy layer may be 2-6 μm.

[0016] The Fe concentration gradient may be 13.5-23 wt % / μm.

[0017] The Fe content of the Al-plated layer may be 8.5-23 wt %.

[0018] In order to ensure the sufficient corrosion resistance and to ensure the mold sticking resistance, the thickness of the Al plating layer may be 3-30 μm.

[0019] The base steel plate may include, by weight%, C: 0.02-0.6%, Si: 0.001-2%, Al: 0.001-1%, Mn: 0.1-4%, P: 0.05% or less, S: 0.02% or less, N: 0.02% or less, Ti: 0-0.1%, B: 0.0001-0.01%, Cu: 0-1.00%, Mo: 0-1.00%, Cr: 0-1.00%, Ni: 0-1.00%, V: 0-1.00%, Ca: 0-0.01%, Nb: 0-0.1%, Sn: 0-1%, W: 0-1%, Sb: 0-1%, Mg: 0-0.1%, Co: 0-1%, As: 0-1%, Zr: 0-1%, Bi: 0-1%, REM: 0-0.3%, and the balance of Fe and impurities.

[0020] Another embodiment of the present invention relates to a method for manufacturing an aluminum-plated steel sheet, which includes the following steps: immersing a base steel sheet in an aluminum (Al) plating bath containing silicon (Si) and allowing the plating solution to adhere to the surface of the base steel sheet; adjusting the plating adhesion amount on the surface of the base steel sheet with an air knife (AirKnife, A / K); and transferring the base steel sheet with the plating solution adhered to a cooling device and cooling it, wherein the K value of the following (Formula 2) satisfies the condition of 200 to 400.

[0021] (Formula 2)

[0022] Where a: Si content in the plating bath (wt%), b: line speed (meters per minute (mpm)), c: A / K interval (mm), d: A / K pressure (kPa), A / K height (mm)

[0023] In order to ensure the coating quality and suppress the generation of dross, the coating bath introduction temperature of the base steel sheet may be 600-680°C.

[0024] The coating adhesion can be 8-80g / m 2 .

[0025] The plating bath may include silicon (Si): 6-12 wt %, iron (Fe): 1-4 wt %, and the balance of aluminum (Al) and inevitable impurities.

[0026] The plating bath may contain 5-13 wt % silicon (Si), 15-35 wt % zinc (Zn), 0.01-5 wt % magnesium (Mg), 0-5 wt % iron (Fe), 0.01-5 wt % manganese (Mn), 0.01-7 wt % chromium (Cr), the balance of aluminum (Al) and inevitable impurities.

[0027] In order to ensure the fluidity of the plating bath and suppress the generation of scum, the temperature of the plating bath may be 600-680°C.

[0028] Another embodiment of the present invention relates to a hot-formed component, which includes a base iron, an Fe-Al alloy plating layer formed on the base iron, and a diffusion layer formed between the base iron and the Fe-Al alloy plating layer, and the hard layer ratio defined by the following (Formula 3) is 50-75%.

[0029] (Formula 3)

[0030] Another embodiment of the present invention relates to a method for manufacturing a hot-formed component, which includes the following steps: using the aluminum-coated steel sheet to manufacture a blank; heating the blank; and forming and cooling the heated blank in a mold.

[0031] (III) Beneficial effects

[0032] When the aluminum-plated steel sheet as an example of the present invention is hot-formed, the adhesion of the mold caused by the coating powder generated by the alloying of the coating can be reduced. Therefore, the quality of the hot-formed parts can be prevented from being reduced, and the stability of the product can be ensured. In addition, the removal operation of the coating powder can be omitted, so the productivity of the product can be improved and the cost can be reduced.

[0033] The multiple beneficial advantages and effects of the present invention are not limited to the above contents, and can be more easily understood in the process of describing the specific embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the result of Fe depth profile of GDOES of Invention Example 2 in the Examples.

[0035] Figure 2 This is a photograph of the test piece observed after the V-bending test in the example.

[0036] Figure 3 This is the measurement result of the amount of powder generated after the V bending test in the example.

[0037] Figure 4 It is the measurement result of the hard layer ratio in Example. Best Mode for Carrying Out the Invention

[0038] Hereinafter, the present invention will be described in detail.

[0039] The terms used in the present invention are used to illustrate the present invention and are not intended to limit the present invention. In addition, unless the relevant definition shows an obviously opposite meaning, the singular form used in this specification also includes the plural form.

[0040] The meaning of “comprising” used in the specification is to specifically describe a configuration, and does not exclude the existence or addition of other configurations.

[0041] Unless otherwise defined, all terms used in this specification, including technical terms and scientific terms, have the same meanings as those generally understood by those skilled in the art. Terms defined in dictionaries are interpreted as meanings consistent with relevant technical documents and currently disclosed contents.

[0042] In the present invention, the component refers to a component or a material for a component manufactured by hot forming. In addition, the steel plate refers to a material before hot forming, and also includes forms such as rolled plates.

[0043] When using coated steel for hot forming, coating powder generated by alloying of the coating is the main cause of die sticking, so it is recognized that it is important to develop a material that minimizes the coating powder during hot forming.

[0044] When the aluminum-plated steel is heated, the Fe of the base iron diffuses to the Al-plated layer to form a Fe-Al alloy coating, and a diffusion layer is formed between the base iron and the Fe-Al alloy coating. In the diffusion layer and the Fe-Al alloy coating, according to the Fe content, starting from the α-Fe with a high Fe content in the base iron part, Fe diffuses in the form of Fe3Al→FeAl→Fe2Al5→FeAl3 and forms a Fe-Al alloy. The part where a large amount of α-Fe, Fe3Al and FeAl with a high Fe content are formed is called a diffusion layer, and the part where a large amount of Fe2Al5 and FeAl3 with a relatively high Al content are formed is called a Fe-Al alloy coating. The hardness of Fe2Al5 and FeAl3 in the Fe-Al alloy is higher than that of α-Fe, Fe3Al, and FeAl, and has a brittle characteristic, so a large amount of powder is generated during hot pressing, which becomes the main cause of the mold adhesion problem during hot forming.

[0045] Therefore, in order to improve the mold adhesion problem, the inventors conducted in-depth research on the following scheme and completed the present invention: that is, when hot forming aluminum-plated steel sheets, the contents of α-Fe, Fe3Al, and FeAl with high Fe content in the Fe-Al alloy can be increased in the alloying of the coating layer, and on the other hand, the ratio of Fe2Al5 and FeAl3 can be reduced.

[0046] First, a specific embodiment of the aluminum-plated steel sheet of the present invention is described in detail.

[0047] The aluminum-plated steel sheet includes a base steel sheet and an Al-plated layer formed on the base steel sheet, and the Al-plated layer includes an alloy layer formed at an interface between the Al-plated layer and the base steel sheet. The alloy layer refers to a layer alloyed by the reaction of the base steel sheet and the Al-plated layer. As an example of forming the alloy layer, when the base steel sheet is immersed in an Al-plating bath, the base steel sheet and the Al-plating bath components may react first and be formed.

[0048] In the Glow Discharge Optical Emission Spectrometry (GDOES) analysis result from the surface of the Al-plated layer along the thickness direction of the base steel plate, the Fe concentration gradient in the range of 40-90 wt % in the Al-plated layer includes 13-26 wt % / μm. Preferably, the Fe concentration gradient in the range of 40.0-90.0 wt % in the Al-plated layer may include 13.0-26.0 wt % / μm.

[0049] As described above, in order to improve mold adhesion, when heating for hot forming, the Fe content is low during the alloying process of the Al-plated layer, so the formation of Fe2Al5 and FeAl3, which have relatively brittle characteristics, is suppressed, and the content of α-Fe, Fe3Al, and FeAl, which have relatively high Fe content, needs to be increased. For this reason, during the hot forming, Fe must be fully diffused into the Al-plated layer in a short time and alloyed.

[0050] According to the first diffusion law (Fick's first law) shown in the following (Formula 1), diffusion occurs from a region with a high concentration to a region with a low concentration, and the higher the concentration gradient, the greater the amount of diffusion.

[0051] (Formula 1)

[0052]

[0053] J B : Flux is the number of atoms passing through a unit area per unit time.

[0054] D B : Diffusion coefficient of B atoms

[0055] C: Concentration

[0056] x: direction

[0057] dC B / dx: Concentration change rate along the x direction

[0058] That is, according to the (Formula 1), the greater the concentration gradient of Fe formed between the Al-plated layer and the base steel sheet in the Al-plated steel sheet, the more feasible the method of increasing the Fe diffusion amount or flux of the base steel sheet in a short time during hot forming. The steeper the Fe concentration gradient, the more the Fe diffusion amount can be increased in a short time during hot forming, and a large amount of alloy phases with a high Fe content are formed in the diffusion layer and alloy layer of the hot-formed part, and the proportion of the brittle alloy phase is reduced.

[0059] In the GDOES analysis results along the thickness direction of the base steel plate from the surface of the Al-plated layer, the Fe concentration gradient in the range of 40-90 wt% in the Al-plated layer is 13-26 wt% / μm, preferably 13.5-23 wt% / μm. Figure 1 , for detailed explanation. Figure 1 This is a graph showing the Fe concentration depth profile from the surface of the plated steel sheet of Inventive Example 2 produced in the following Examples by glow discharge optical emission spectroscopy (GDOES).

[0060] like Figure 1 As shown, when the Fe concentration gradient is analyzed by GDOES depth profiling from the Al-plated layer surface along the thickness direction inside the base steel plate, the Fe content gradient observed from the Al-plated layer surface changes in a pattern of first being gentle, then rapidly increasing, and then being gentle again. Thus, an alloy layer formed at the interface with the base steel plate was confirmed, and it can be confirmed that the thickness of the alloy layer is about 2-6 μm. That is, the inflection point where the Fe gradient of the alloy layer and the Fe gradient in the plating layer change was confirmed in the GDOES distribution (refer to Figure 1 The inflection point can be considered as an indicator that can distinguish the AlSi coating layer and the alloy layer (AlSiFe) in the Al coating layer, and the alloy layer can be distinguished by the inflection point. In the GDOES distribution, the position of the inflection point where the Fe gradient changes in the Fe content (weight %) distribution diagram mainly exists between 30 weight % and 60 weight %. Therefore, in order to define the concentration gradient of the Fe in more detail, the concentration gradient value of the Fe is limited to between 40 weight % and 90 weight %, and the concentration gradient value of the Fe interval of 40-90 weight % is measured.

[0061] When the Fe content in the Al-plated layer is in the range of 40-90 wt% and the Fe concentration gradient is less than 13 wt% / μm, it is the characteristic of a conventional Al-plated steel sheet, and is not the Al-plated steel sheet with improved mold adhesion to be developed by the present invention. When the Fe concentration gradient exceeds 26 wt% / μm, since the thickness of the alloy layer in the Al-plated steel sheet is too thin, the Fe of the base material iron can easily destroy the thin alloy layer during hot forming of the Al-plated steel sheet, resulting in rapid diffusion, thereby forming an uneven alloy layer, which may lead to reduced corrosion resistance.

[0062] It is effective when the Fe content of the Al-plated layer is 8-24 wt %, preferably 8.0-24.0 wt %, and more preferably 8.5-23 wt %.

[0063] As an example of a method for measuring the content of Fe in the Al-plated layer, a circular coating with a radius of 25 mm is melted and measured by inductively coupled plasma (ICP). As a specific method, a circular Al-plated layer with a radius of 25 mm is dissolved once in a 20% NaOH solution, and the coating is dissolved twice in a solution to which HCl and an inhibitor are added at a ratio of 1:3, and then the solution containing the primary dissolution solution and the secondary dissolution solution is analyzed by ICP to measure the content of Al, Si and Fe. The content of Fe at this time should be 8-24% by weight in the present invention, and more preferably 8.5-23% by weight is effective.

[0064] The Fe content in the Fe profile of GDOES can also be obtained by integrating the Fe profile, but the GDOES profile represents the Fe content at the corresponding position along the thickness direction, so it is somewhat difficult to observe the content of the components contained in the entire coating. In contrast, ICP analysis performs component analysis on the sample of the dissolved coating, and the Fe content contained in the entire coating including the Al alloy layer can be obtained, so the content measurement data is highly reliable.

[0065] In addition, when the Fe content of the Al-plated layer is less than 8 wt %, it has the characteristics of a conventional Al-plated steel sheet, and is not the Al-plated steel sheet with improved mold adhesion to be developed by the present invention. When the Fe content of the Al-plated layer exceeds 24 wt %, when the difference between the Fe content in the coating and the Fe content in the base steel sheet is large enough, the Fe diffusion during hot forming can be promoted. However, when the Fe content in the coating exceeds 24 wt %, there is no large difference between the Fe content in the base steel sheet and the Fe content in the coating, which may cause the problem of slow diffusion of Fe in the base iron into the Al-plated steel sheet during hot forming.

[0066] The Al-plated layer may be an Al-based plating widely used in hot-formed plated steel sheets by a person skilled in the art of the hot-formed plated steel sheets to which the present invention belongs, and the content or type of the component is not particularly limited. It includes not only pure Al plating, but also plating in which Al contains part of Si, plating in which Al contains part of Zn, plating in which Al contains part of Si, Mg, Zn, Fe, etc., or more.

[0067] The Al-plated layer is effective when the thickness is 3 μm to 30 μm, preferably 3.0-30.0 μm, and more preferably 4 μm to 26 μm.

[0068] When the thickness of the Al-plated layer is less than 3 μm, a large amount of unplated areas occur on the surface of the Al-plated steel sheet due to the excessively thin thickness of the coating, which may affect the corrosion resistance of the component after hot forming. When the thickness of the Al-plated layer exceeds 30 μm, even if the Fe of the base material iron diffuses rapidly during hot forming, due to the thick thickness of the coating and the high fraction of the brittle phase, it may be difficult to improve the mold adhesion.

[0069] In addition, the base steel plate is not particularly limited as long as it is a steel plate that can be used for hot forming. There are no particular restrictions on the classification of hot-rolled steel plates, cold-rolled steel plates, etc. according to the manufacturing process, and there are no particular restrictions on the steel types and alloy component systems such as dual phase steel (DP), composite steel, TRIP steel, and TWIP steel.

[0070] As a specific example, 22MnB5 steel is represented, which may contain, by weight % (wt.%): carbon (C): 0.1-0.3%, manganese (Mn): 1.0-2.0%, silicon (Si): 0.02-0.30%, boron (B): 5-45ppm, and the rest includes inevitable impurities and iron (Fe).

[0071] In addition, the base steel plate may have a chemical composition of, by weight%, carbon (C): 0.02-0.6%, silicon (Si): 0.001-2%, aluminum (Al): 0.001-1%, manganese (Mn): 0.1-4%, phosphorus (P): 0.05% or less, sulfur (S): 0.02% or less, nitrogen (N): 0.02% or less, titanium (Ti): 0-0.1%, boron (B): 0.0001-0.01%, copper (Cu): 0-1.00%, molybdenum (Mo): 0-1.00%, chromium (Cr): : 0-1.00%, nickel (Ni): 0-1.00%, vanadium (V): 0-1.00%, calcium (Ca): 0-0.01%, niobium (Nb): 0-0.1%, tin (Sn): 0-1%, tungsten (W): 0-1%, antimony (Sb): 0-1%, magnesium (Mg): 0-0.1%, cobalt (Co): 0-1%, arsenic (As): 0-1%, zirconium (Zr): 0-1%, bismuth (Bi): 0-1%, rare earth metal (REM): 0-0.3%, and the remainder of Fe and impurities.

[0072] Next, a specific embodiment of a method for manufacturing an aluminum-plated steel sheet according to an example of the present invention is described in detail. The method for manufacturing an aluminum-plated steel sheet comprises the following steps: immersing a base steel sheet in a plating bath and attaching the plating solution to the surface of the base steel sheet; adjusting the amount of plating attached to the surface of the base steel sheet; and transferring the base steel sheet to which the plating solution is attached to a cooling device. Each step is described in detail below.

[0073] First, the base steel sheet is immersed in a plating bath and the plating solution is attached to the surface of the base steel sheet.

[0074] As described above, the base steel plate has no particular restrictions on the object, steel type, etc. as long as it can be used as a hot-formed component. Before immersing the base steel plate in the plating bath, the base steel plate can be heated to a certain temperature (introduction temperature). At this time, an introduction temperature of 600-680°C is effective. Preferably, it is more effective when it is 600.0-680.0°C. Heating the base steel plate to the introduction temperature allows the molten aluminum to solidify rapidly on the surface of the steel plate, which can prevent deviations in the amount of plating adhesion or problems with unplating due to reduced fluidity. However, excessive heating may promote the melting of the steel plate and may accelerate the generation of slag.

[0075] The plating bath may be an Al-based plating bath for forming an Al-plated layer, and any plating bath may be used without limitation in the present invention as long as it can be applied to plating of a plated steel sheet for hot forming.

[0076] As an example, the plating bath composition may include: silicon (Si): 6-12 wt%, iron (Fe): 1-4 wt%, the balance of aluminum (Al) and inevitable impurities. As another example, the plating bath composition may include: 5-13 wt% silicon (Si), 15-35 wt% zinc (Zn), 0.01-5 wt% magnesium (Mg), 0-5 wt% iron (Fe), 0.01-5 wt% manganese (Mn), 0.01-7 wt% chromium (Cr), the balance of aluminum (Al) and inevitable impurities.

[0077] The temperature of the plating bath is effective when it is 600-680° C., preferably 600.0-680.0° C. It is more effective. When the temperature of the plating bath is too low, the fluidity of the plating solution in the plating bath may decrease, and on the other hand, when the temperature of the plating bath is too high, the generation of scum in the plating bath may increase.

[0078] Next, the coating adhesion amount of the base steel plate is adjusted. The device or method for adjusting the coating adhesion amount is not particularly limited and can be performed by a method commonly performed in the technical field to which the present invention belongs. As an example, an air knife (Air Knife, A / K) is used.

[0079] The coating adhesion is 8-80g / m based on one side. 2 , the coating thickness is 3-30 μm, which is effective. Preferably, the coating adhesion is 8.0-80.0 g / m based on a single side. 2 , it is more effective when the coating thickness is 3.0-30.0μm. The coating adhesion of Al plating can usually be converted to the coating adhesion when the coating thickness is x 2.7. When the coating thickness of 3-30μm is converted into the coating adhesion, it is about 8-80g / m 2 The more preferred thickness is 4-26 μm and the plating adhesion is 10-70 g / m 2 .

[0080] The base steel sheet with the adjusted coating amount is transferred to a cooling device and cooled. When the base steel sheet with the coating solution enters the cooling device, rapid cooling begins, and the reaction of the alloy layer in the Al-plated layer may stop. An example of the cooling device includes a cooling tower.

[0081] The manufacturing method is effective when the K value defined by the following formula 2 is 200 to 400.

[0082] The formula 2 can be calculated as follows.

[0083] (Formula 2)

[0084] Wherein a: Si content in the plating bath (weight %), b: line speed (m / min), c: A / K interval (mm), d: A / K pressure (kPa), A / K height (mm), line speed refers to the speed of passing through the plating bath and transferring, the interval of the air knife (A / K) used to adjust the coating adhesion amount refers to the interval between the steel plate and the air knife, and the A / K height refers to the distance from the plating bath to the A / K.

[0085] In order to manufacture a plated steel sheet with improved adhesion resistance of the mold, the (Formula 2) takes into account the respective characteristics of various variables that determine the characteristics of the coating. The technical significance lies in taking into account the influencing factors and their correlation when manufacturing the plated steel sheet for the purpose of improving adhesion resistance.

[0086] In order to manufacture a steel sheet with improved anti-sticking property of a mold, various process factors such as the Si content of the plating bath, the plating bath temperature, the introduction temperature, the line speed, the A / K interval, the A / K pressure, the A / K height, and the cooling speed of the cooling tower are considered, and it is necessary to optimize the Si content in the plating bath, the line speed, the A / K interval, the A / K pressure, and the A / K height, thereby obtaining the (Formula 2). When the K value of the (Formula 2) is 200 to 400, the anti-sticking property of the mold can be improved. Preferably, the K value is more effective when it is 200.0 to 400.0.

[0087] Specifically, when the K value is less than 200, the A / K pressure is insufficient to improve the resistance to mold adhesion, or the line speed, A / K interval, and A / K height are low, so it is difficult to improve the adhesion. When the K value exceeds 400, the A / K pressure is too high or the line speed, A / K interval, and A / K height are higher than the appropriate values, so it is difficult to improve the adhesion.

[0088] Before the base steel sheet is immersed in the plating bath, it can be provided in various ways. As an example, after the blank is heated, it can be manufactured by processes including hot rolling, coiling, cold rolling, annealing, etc. The specific process conditions of heating, hot rolling, coiling, cold rolling, annealing, etc. of the blank required can vary according to the required properties of the base steel sheet, and therefore are not particularly limited.

[0089] Next, a specific embodiment of the thermoformed component of the present invention will be described in detail.

[0090] The hot-formed component of the present invention includes a base iron, a Fe-Al alloy plating layer formed on the base iron, and a diffusion layer formed between the Fe-Al alloy plating layer and the base iron.

[0091] The Fe-Al alloy coating and diffusion layer refer to alloying by mutual diffusion and reaction of coating components and substrate iron components during heating of aluminum-plated steel sheet. In the diffusion layer and Fe-Al alloy coating, the portion of α-Fe, Fe3Al and FeAl with high Fe content formed in large quantities is called diffusion layer, and the portion of Fe2Al5 and FeAl3 with relatively high Al content formed in large quantities is called Fe-Al alloy coating. The diffusion layer and Fe-Al alloy coating can be optically confirmed by etching the cross section of the hot-formed part with nitric acid alcohol (Nital). The diffusion layer is the first layer that exists directly above the substrate iron that is transformed into martensite, and from the second layer thereafter, it can be regarded as Fe-Al alloy coating.

[0092] The thermoformed part is effective when the hard layer ratio defined by the following (Formula 3) is 50-75%. Preferably, the hard layer ratio is more effective when it is 50.0-75.0%.

[0093] (Formula 3)

[0094] When the hard layer rate exceeds 75%, the heating time during hot forming must be further extended, which may lead to a decrease in the productivity of the component forming material. Therefore, it is effective to make the hard layer rate as low as 75% or less within the range that does not reduce the productivity in the conventional heating time. In addition, when the hard layer rate is less than 50%, it is difficult to regard the hot-formed part of the Al-plated steel plate with improved mold sticking resistance due to the hard layer rate that may appear in the hot-formed parts of the Al-plated steel plate.

[0095] When the base iron of the hot-formed component is compared with the base steel sheet of the above-mentioned hot-formed plated steel sheet, the difference in alloy composition is not large, but there may be a difference in microstructure, so it is preferable to distinguish them. Therefore, in the present invention, it is distinguished that the base steel sheet is used in the hot-formed plated steel sheet, and the base iron is used in the hot-formed component. On the other hand, in the case of the base steel sheet of the hot-formed plated steel sheet, although ferrite and pearlite structures are formed, martensite is formed as the main phase in the base iron of the hot-formed component formed by hot forming, and bainite may be partially formed.

[0096] Next, a specific embodiment of the method for manufacturing a hot-formed component of the present invention is described in detail. For this purpose, a blank is provided. As an example of the steel blank, the above-mentioned aluminum-plated steel sheet can be used for manufacturing.

[0097] The provided blank is preferably heated to a temperature above the austenite single phase region temperature, more specifically to a temperature range of Ac3 to 975°C. When the heating temperature is lower than the Ac3 temperature, it is difficult to ensure strength and collision resistance due to the presence of untransformed ferrite between the two-phase regions. On the other hand, when the heating temperature exceeds 975°C, too much oxide is generated on the surface of the component, so it is difficult to ensure spot weldability, and the manufacturing cost for maintaining high temperature increases. The blank heated as described above is preferably maintained within the above temperature range for 1-1000 seconds. When the holding time is less than 1 second, uniform temperature distribution throughout the blank is difficult, so material deviations may be caused at each position. When the holding time exceeds 1000 seconds, it is difficult to ensure spot weldability due to excessive oxides generated on the surface, and the manufacturing cost of the component may be increased.

[0098] The heated blank is transferred to a press and subjected to forming and cooling. At this time, the cooling rate is preferably above 20°C / second. The cooling rate is more preferably above 20.0°C / second. When the cooling rate is less than 20°C / second, a ferrite phase is introduced during the cooling process and generated at the grain boundaries, and physical properties such as strength and collision resistance may deteriorate. The process of transferring, forming and cooling the blank is not particularly limited, and for the hot forming process, the commonly used process can be directly applied. DETAILED DESCRIPTION

[0099] The following are examples of the present invention. Of course, those skilled in the art may make various changes to the following examples without departing from the scope of the present invention. The following examples are provided for understanding the present invention, and the scope of the present invention is not limited to the following examples. The scope of the present invention should be determined by the claims and their equivalents.

[0100] (Example)

[0101] In the embodiment of the present invention, a conventional 22MnB5 base steel sheet is prepared and immersed in a plating bath containing about 9-10 wt % Si and the rest containing Al and inevitable impurities, thereby manufacturing an aluminum-plated steel sheet. At this time, the temperature of the plating bath is 640-670°C, and the introduction temperature of the base steel sheet is 650-680°C.

[0102] In order to manufacture the plated steel sheet, the Si content in the plating bath and the steel sheet transfer speed (line speed) are adjusted, and the single-sided plating adhesion amount is adjusted to 10-80 g / m 2 The coating adhesion amount was adjusted by an air knife (A / K), and the coating was transferred to a cooling tower as a cooling device for cooling. The process conditions at this time are shown in Table 1.

[0103] [Table 1]

[0104]

[0105] The formula 2 can be calculated as follows.

[0106] (Formula 2)

[0107] Wherein, a: Si content in the plating bath (wt %), b: line speed (m / min), c: A / K interval (mm), d: A / K pressure (kPa), A / K height (mm).

[0108] For the aluminum-plated steel sheets produced as described above, the concentration gradient of Fe in the Al-plated layer and the alloy composition of the Al-plated layer were measured and are shown in Table 2 together.

[0109] As for the Fe concentration gradient, the Fe concentration gradient in the range of 40-90 wt % was obtained from the result of GDOES analysis of the Al-plated steel sheet from the surface of the Al-plated layer in the depth direction. As for the alloy composition, the Al-plated layer was dissolved once in a 20% NaOH solution, the entire coating layer was dissolved (secondarily) in a solution to which HCl and an inhibitor were added at a ratio of 1:3, and then the entire solution containing the primary solution and the secondary solution was analyzed by ICP to measure the contents of Al, Si and Fe.

[0110] [Table 2]

[0111]

[0112] Figure 1 This is a graph showing the Fe concentration distribution of the GDOES of Invention Example 2 in Table 2.

[0113] The aluminum-plated steel sheets produced as shown in Tables 1 and 2 were evaluated for anti-die sticking properties. The results are shown below. Figures 2 to 3 And in the following Table 3. In particular, in the embodiments, for Comparative Examples 1 and 4 and Inventive Examples 1 and 3, Figure 2 Table 3 shows photographs for evaluating the anti-mold sticking property. Figure 2 (a) and (b) are photographs of Comparative Examples 1 and 4, and (c) and (d) are photographs of Inventive Examples 1 and 3.

[0114] In order to confirm the anti-mold sticking property, parts were manufactured by heat treating each test piece at 900°C for 5 minutes, and the powdering property of the heat-treated parts was evaluated by V-bending test method (conditions: 20°, 2R). The cause of sticking is that a large amount of powder dropped from the plating layer is piled up during the die stamping process, and the powder is not removed in time. Therefore, the anti-mold sticking property can be confirmed by evaluating the powdering property.

[0115] The evaluation of the powdering property is carried out by cutting the heat-treated test piece into 60×30 mm and then conducting a V-bending test. The experimental conditions are 20° and 2R. The weight before and after the test is measured and the results are shown in Table 3. Figure 2 The following is a photograph showing the results of the V-bend test of some of the test pieces in Table 3. Figure 3 The amount of powder generated in each test piece in Table 2 (average weight reduction) is shown in a graph.

[0116] [Table 3]

[0117]

[0118] From Table 3 and Figures 2 to 3As can be seen from the results, it can be seen that the generation of plating powder in the hot forming process of the aluminum-plated steel sheet corresponding to the inventive example that meets the range proposed by the present invention is significantly reduced.

[0119] In addition, for each test piece in Table 2 that was subjected to the above heat treatment, it was confirmed that the alloyed plating layer formed a diffusion layer and a Fe-Al alloy plating layer, and the hard layer ratio was measured. The results are shown in FIG. Figure 4 In order to measure the hard layer ratio, each test piece was optically observed through a cross section to measure the thickness of the Fe-Al alloy coating layer and the diffusion layer. The hard layer ratio was calculated by the following (Formula 3).

[0120] (Formula 3)

[0121] From the said Figure 4 As can be seen from the results, the hard layer rate of the comparative example is higher than that of the inventive example.

[0122] Therefore, in the inventive example according to the present invention, not only a large amount of Fe exists in the plating layer in the plated steel sheet, but also the Fe gradient in the alloy layer is large, so a large amount of Fe can diffuse, so the proportion of the diffusion layer after heat treatment is high, the hard layer rate is reduced, and thus the amount of powdering generated is reduced.

Claims

1. An aluminum-plated steel sheet, comprising a base steel sheet and an Al-plated layer formed on the base steel sheet, From the GDOES analysis results of the surface of the Al-plated layer along the thickness direction, the Fe concentration gradient in the range of 40-90 wt % in the Al-plated layer is 13-26 wt % / μm. The Fe content of the Al-plated layer is 8-24% by weight.

2. The aluminum-plated steel sheet according to claim 1, wherein: The Al-plated layer includes an alloy layer formed at the interface between the Al-plated layer and the base steel plate, and the thickness of the alloy layer is 2-6 μm.

3. The aluminum-plated steel sheet according to claim 1 or 2, wherein: The Fe concentration gradient is 13.5-23 wt % / μm.

4. The aluminum-plated steel sheet according to any one of claims 1 to 3, wherein: The Fe content of the Al-plated layer is 8.5-23% by weight.

5. The aluminum-plated steel sheet according to any one of claims 1 to 4, wherein: The thickness of the Al-plated layer is 3-30 μm.

6. The aluminum-plated steel sheet according to any one of claims 1 to 5, wherein: In terms of weight %, the base steel plate comprises C: 0.02-0.6%, Si: 0.001-2%, Al: 0.001-1%, Mn: 0.1-4%, P: less than 0.05%, S: Less than 0.02%, N: less than 0.02%, Ti: 0-0.1%, B: 0.0001-0.01%, Cu: 0-1.00%, Mo: 0-1.00%, Cr: 0-1.00%, Ni: 0-1.00%, V: 0-1.00%, Ca: 0-0.01%, Nb: 0-0.1%, Sn: 0-1%, W: 0-1%, Sb: 0-1%, Mg: 0-0.1%, Co: 0-1%, As: 0-1%, Zr: 0-1%, Bi: 0-1%, REM: 0-0.3%, the balance is Fe and impurities.

7. A method for manufacturing an aluminum-plated steel plate, comprising the following steps: immersing the base steel sheet in an aluminum (Al) plating bath containing silicon (Si) and allowing the plating solution to adhere to the surface of the base steel sheet; adjusting the coating adhesion amount on the surface of the base steel plate by using an air knife (A / K); as well as The base steel plate with the plating solution attached is transferred to the cooling device and cooled. Wherein, the K value of the following formula 2 satisfies the condition of 200 to 400, (Formula 2) Wherein, a: Si content in the plating bath, unit is weight %, b: line speed, unit is meter / minute (mpm), c: A / K interval, unit is mm, d: A / K pressure, unit is kPa, A / K height, unit is mm.

8. The method for manufacturing an aluminum-plated steel sheet according to claim 7, wherein: The base steel sheet has a plating bath introduction temperature of 600-680°C.

9. The method for producing an aluminum-plated steel sheet according to claim 7 or 8, wherein: The coating adhesion is 8-80g / m 2 .

10. The method for producing an aluminum-plated steel sheet according to any one of claims 7 to 9, wherein: The plating bath contains: silicon (Si): 6-12 wt %, iron (Fe): 1-4 wt %, and the balance of aluminum (Al) and inevitable impurities.

11. The method for producing an aluminum-plated steel sheet according to any one of claims 7 to 9, wherein: The plating bath comprises: 5-13 wt % of silicon (Si), 15-35 wt % of zinc (Zn), 0.01-5 wt % of magnesium (Mg), 0-5 wt % of iron (Fe), 0.01-5 wt % of manganese (Mn), 0.01-7 wt % of chromium (Cr), the balance of aluminum (Al) and inevitable impurities.

12. The method for producing an aluminum-plated steel sheet according to any one of claims 7 to 11, wherein: The temperature of the plating bath is 600-680°C.

13. A hot-formed component comprising a base iron, a Fe-Al alloy plating layer formed on the base iron, and a diffusion layer formed between the base iron and the Fe-Al alloy plating layer, The hard layer ratio defined by the following (Formula 3) is 50-75%, (Formula 3) .

14. A method for manufacturing a thermoformed component, comprising the following steps: Using the aluminum-plated steel sheet according to any one of claims 1 to 6 to manufacture a blank; heating the blank; and The heated blank is formed and cooled in the mold.

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