Plated steel sheet and method for manufacturing same

Abstract

The present invention relates to a plated steel sheet and a method for manufacturing the same, and more particularly, to a plated steel sheet having excellent bendability and a method for manufacturing the same.

Description

Technical Field

[0001] The present invention relates to a plated steel sheet and a method for manufacturing the same, and more particularly, to a plated steel sheet having excellent bendability and a method for manufacturing the same. Background Art

[0002] In recent years, in order to improve fuel efficiency and meet CO2 emission regulations, etc., automobile manufacturers have been continuously researching vehicle lightweighting. Therefore, in order to increase the strength of steel materials under the same weight, various alloying elements are included, but problems such as increased hardenability and deteriorated workability such as springback phenomenon occur.

[0003] To solve these problems, a hot stamping method has been proposed. The hot stamping method is a technique in which steel materials having a certain strength are processed in the austenite single-phase region and then rapidly cooled to a low temperature, thereby forming low-temperature structures such as martensite in the steel materials, and significantly increasing the strength of the products. By this method, when forming components with high strength, the problem of workability can be minimized.

[0004] In addition, bendability is becoming a representative physical property for evaluating the crashworthiness of components formed by the hot stamping method. However, it is known that due to the strength of the components themselves and martensite that is easily affected by bendability in terms of microstructure, the bendability of components formed by the hot stamping method is poor. To improve this, various methods have been tried to improve the characteristics of the materials, for example, adding trace elements to the steel, or controlling the microstructure during cold rolling and annealing, etc. Summary of the Invention

[0005] (1) Technical Problems to be Solved

[0006] An object of an embodiment of the present invention is to provide a plated steel sheet and a method for manufacturing the same.

[0007] An object of an embodiment of the present invention is to provide a plated steel sheet having excellent bendability and a method for manufacturing the same.

[0008] The technical problems of the present invention are not limited to the above. Those of ordinary skill in the art can easily understand additional technical problems of the present invention from the overall content of this specification.

[0009] (2) Technical Solutions

[0010] According to an embodiment of the present invention, a plated steel sheet can be provided, which includes: a base steel sheet; and a plating layer formed on the base steel sheet. By weight%, the plating layer contains Zn: 24.0 - 27.0%, Si: 7.0 - 10.0%, Fe: 6.0 - 10.0%, the balance being Al and inevitable impurities. Among them, the base steel sheet includes a ferrite layer formed along the thickness direction of the base steel sheet from the interface between the base steel sheet and the plating layer.

[0011] The R value defined by the following relational expression 1 of the plating layer can be 400.0 to 500.0.

[0012] [Relational Expression 1]

[0013] R = -1.21 [Al] - 1.28 [Si] - 1.98 [Fe] - 3.17 [Zn] + 631.86

[0014] (In the formula, [Al], [Si], [Fe], and [Zn] are the weight percentages of each element.)

[0015] When analyzed by a Glow Discharge optical emission Spectrometer (GDS), the intersection point of Zn and Al in the plating layer can exist within a depth of 5 μm along the thickness direction from the outermost surface of the plating layer.

[0016] The thickness of the ferrite layer can be 70 - 80 μm.

[0017] The coating weight of the plating layer can be 40 - 60 g / m 2 .

[0018] The hardness of the plated steel sheet can be 400 - 500 Hv.

[0019] When the plated steel sheet is subjected to a bending test after hot forming, the maximum bending angle can be 70 degrees or more.

[0020] By weight%, the base steel sheet can contain 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, B: 0.0001 - 0.01%, the balance being Fe and impurities.

[0021] By weight percentage, the base steel plate may further contain one or more selected from Ti: 0.1% or less, Cu: 1.00% or less, Mo: 1.00% or less, Cr: 1.00% or less, Ni: 1.00% or less, V: 1.00% or less, Ca: 0.01% or less, Nb: 0.1% or less, Sn: 1% or less, W: 1% or less, Sb: 1% or less, Mg: 0.1% or less, Co: 1% or less, As: 1% or less, Zr: 1% or less, Bi: 1% or less, REM: 0.3% or less.

[0022] According to an embodiment of the present invention, a method for manufacturing a plated steel plate can be provided, which includes the following steps: preparing a base steel plate; heating the prepared base steel plate to a temperature range of 600 - 950 °C and annealing it at a dew point temperature of 5 - 20 °C; and immersing the annealed base steel plate in a plating bath for plating. By weight percentage, the plating bath contains Zn: 26.0 - 30.0%, Si: 6.0 - 9.0%, the balance being Al and inevitable impurities.

[0023] The annealing step can be maintained for 100 - 500 seconds in a gas atmosphere containing 70% or more of H2 and the balance being N2.

[0024] The temperature of the plating bath can be 580 - 680 °C.

[0025] (III) Beneficial effects

[0026] According to an embodiment of the present invention, a plated steel plate and a method for manufacturing the same can be provided.

[0027] According to an embodiment of the present invention, a plated steel plate having excellent bendability and a method for manufacturing the same can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a photograph of observing the cross-section in the thickness direction of Invention Example 4 of an embodiment of the present invention.

[0029] Figure 2 is a photograph of measuring Invention Example 4 of an embodiment of the present invention by the glow discharge spectrometer (GDS) analysis method. BEST MODE FOR CARRYING OUT THE INVENTION

[0030] The following describes the preferred specific embodiments of the present invention. The specific embodiments of the present invention can be modified into various forms, and the scope of the present invention should not be construed as being limited to the specific embodiments described below. These specific embodiments are provided to more specifically explain the present invention to those of ordinary skill in the technical field to which the present invention pertains.

[0031] In order to improve the problems of the above-mentioned prior art, the present inventors have confirmed that the present invention has been completed by appropriately forming a ferrite layer on the surface of the base steel plate and optimizing the composition of the coating layer, thereby ensuring excellent bendability.

[0032] Hereinafter, the present invention will be described in detail.

[0033] The coated steel plate according to an embodiment of the present invention may include: a base steel plate; and a coating layer formed on the base steel plate.

[0034] Base steel plate

[0035] The alloy composition of the base steel plate according to an embodiment of the present invention is not particularly limited. However, according to an embodiment of the present invention, by weight%, the base steel plate may contain 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, B: 0.0001 - 0.01%, the balance being Fe and impurities.

[0036] In addition to the above composition, the base steel plate of the present invention may contain the balance of iron (Fe) and inevitable impurities. Inevitable impurities may be inadvertently mixed in during the normal manufacturing process, so it is impossible to exclude these impurities. These impurities are well known to those skilled in the art of ordinary steelmaking manufacturing, so all of their contents are not particularly mentioned in this specification.

[0037] Furthermore, the base steel plate according to an embodiment of the present invention may optionally contain, by weight%, one or more selected from Ti: 0.1% or less, Cu: 1.00% or less, Mo: 1.00% or less, Cr: 1.00% or less, Ni: 1.00% or less, V: 1.00% or less, Ca: 0.01% or less, Nb: 0.1% or less, Sn: 1% or less, W: 1% or less, Sb: 1% or less, Mg: 0.1% or less, Co: 1% or less, As: 1% or less, Zr: 1% or less, Bi: 1% or less, REM: 0.3% or less as needed.

[0038] The base steel plate according to an embodiment of the present invention may include a ferrite layer with a thickness of 70 - 80 μm along the thickness direction of the base steel plate from the interface between the base steel plate and the coating layer.

[0039] In the present invention, in order to improve bendability, a ferrite layer can be formed along the thickness direction of the base steel sheet from the interface between the base steel sheet and the coating. In the ferrite layer according to an embodiment of the present invention, it may contain 90% or more of ferrite by area%, and the remaining portion may contain one or more of pearlite, bainite, and retained austenite. According to an embodiment of the present invention, it may contain 95% or more of ferrite by area%. The microstructure of the base steel sheet according to an embodiment of the present invention may be a duplex structure composed of ferrite and pearlite, or a triple-phase structure including bainite or retained austenite in ferrite and pearlite.

[0040] Generally, during hot stamping, martensite, which is a low-temperature structure, is mainly formed. Due to the characteristics of high-hardness martensite, it may be difficult to have excellent bendability. Therefore, in the present invention, by introducing ferrite, which is a soft phase, into the surface layer of the base steel sheet, during subsequent hot stamping, even if a martensite phase transformation occurs, compared with the existing structure composed of a combination of two or more of ferrite, pearlite, bainite, or retained austenite as the matrix phase, the bendability can be improved without significantly reducing the strength. In the present invention, in order to ensure the above effects, the thickness of the ferrite layer can be limited to 70 μm or more. However, when the area where ferrite is formed exceeds 80 μm, the strength after hot forming may be poor. Therefore, in order to ensure bendability while maintaining strength, its upper limit can be limited to 80 μm.

[0041] Coating

[0042] The coated steel sheet according to an embodiment of the present invention may include a coating formed on the base steel sheet. By weight%, the coating may contain Zn: 24.0 - 27.0%, Si: 7.0 - 10.0%, Fe: 6.0 - 10.0%, and the balance Al and inevitable impurities.

[0043] Zn in the coating forms an Al-Zn phase, thereby ensuring sacrificial corrosion protection performance. In order to ensure the above effects, 24.0 - 27.0% of Zn may be included in the present invention. When the content of Zn is less than 24.0%, there is a possibility of reducing the sacrificial corrosion protection performance. According to an embodiment of the present invention, the content of Zn can be limited to 25.0% or more. On the other hand, when the content of Zn in the coating exceeds 27.0%, there may be a problem of generating microcracks. According to an embodiment of the present invention, 26.5% or less of Zn may be included.

[0044] In addition, when the Si content in the coating layer is less than 7.0%, the thickness of the FeAl3 and Fe2Al5 intermetallic compounds becomes too thick, and there may be a problem of material brittleness. According to an embodiment of the present invention, the Si content can be limited to 7.5% or more. On the other hand, when the Si content exceeds 10.0%, the effect of reducing the thickness of the intermetallic compound brought by adding Si may be reduced, and there may be a problem of Si precipitation. According to an embodiment of the present invention, the Si content can be 10.0% or less. According to an embodiment of the present invention, the Si content can be 9.5% or less.

[0045] Fe in the coating layer may be mixed in from the base steel plate due to the diffusion caused by the latent heat of the material after plating. In the present invention, 6.0 - 10.0% of Fe can be included. Fe in the coating layer can form an Fe - Al phase at the interface between the base steel plate and the coating layer, thereby preventing direct contact between Zn in the coating layer and Fe of the base steel plate and inhibiting the diffusion of Zn into the base steel plate, thus having the effect of blocking microcracks. When Fe in the coating layer is less than 6.0%, due to the formation of an uneven Al - Fe alloy phase, there may be problems such as the plating surface becoming rough and the plating defects increasing. According to an embodiment of the present invention, the Fe content can be limited to 7.0% or more. On the other hand, when the Fe content of the coating layer exceeds 10.0%, a brittle Al - Fe - based interface alloy layer is formed, and thus there may be problems of material anisotropy and the coating layer peeling off during processing. According to an embodiment of the present invention, 9.5% or less of Fe can be included.

[0046] According to an embodiment of the present invention, the R value defined by the following relational expression 1 of the coating layer can be 400.0 to 500.0.

[0047] [Relational Expression 1]

[0048] R = -1.21 [Al] - 1.28 [Si] - 1.98 [Fe] - 3.17 [Zn] + 631.86

[0049] (In the formula, [Al], [Si], [Fe], and [Zn] are the weight percentages of each element.)

[0050] In the present invention, in order to confirm the influence of each component of the coating layer on the hardness (Hv), the relationship between the element content (weight percentage) of the overall cross - section of the coating layer and the hardness (Hv) value is derived. It is confirmed that when the R value defined by the relational expression 1 satisfies 400.0 to 500.0, the material can have sacrificial corrosion protection performance, and during hot - press forming, the generation of microcracks can be inhibited.

[0051] When the R value defined in the above-mentioned relational expression 1 is less than 400.0, the effect of sacrificing corrosion resistance performance may be insufficient. According to an embodiment of the present invention, the R value can be 410.0 or more. On the other hand, when the R value defined in the relational expression 1 exceeds 500.0, during hot press forming, a primary Zn phase may be formed on the surface layer, and excessive Zn oxides may be generated. In addition, during hot press forming, there may be a problem of generating microcracks. According to an embodiment of the present invention, the R value can be 480.0 or less. According to an embodiment of the present invention, the R value can be 460.0 or less.

[0052] For the coating according to an embodiment of the present invention, when analyzed by a glow discharge spectrometer (GDS), the intersection of Zn and Al can exist within a depth of 5 μm in the thickness direction from the outermost surface of the coating.

[0053] In the present invention, in order to impart sacrificial corrosion resistance performance to the material and prevent the generation of microcracks during hot press forming, the position of the intersection of Zn and Al in the coating can be restricted. When the position of the intersection exceeds a depth of 5.0 μm in the thickness direction from the outermost surface of the coating, during hot press forming, a primary Zn phase may be formed on the surface layer, and there may be a problem of forming excessive Zn oxides.

[0054] The coating amount of the coating according to an embodiment of the present invention can be 40 - 60 g / m 2 。

[0055] When the coating amount of the coating is less than 40 g / m 2 , after hot forming, due to excessive diffusion of Fe, problems such as poor corrosion resistance may occur during use. On the other hand, when the coating amount of the coating exceeds 60 g / m 2 , the aluminum content in the coating relatively increases, and there may be a problem of poor bendability.

[0056] The hardness of the coating of the coated steel sheet according to an embodiment of the present invention can be 400 - 500 Hv, and the maximum bending angle during the bending test after hot forming can be 70 degrees or more, ensuring excellent strength and bendability characteristics.

[0057] In the present invention, the evaluation of bendability is to set the direction parallel to the rolling direction as the bending test axis direction and measure the maximum angle without generating cracks.

[0058] Hereinafter, the manufacturing method of the coated steel sheet of the present invention will be described in detail.

[0059] The coated steel sheet according to an embodiment of the present invention can be manufactured by preparing a base steel sheet satisfying the alloy composition of the present invention and performing annealing and coating.

[0060] Preparation of the base steel plate

[0061] A base steel plate having an alloy composition satisfying an embodiment of the present invention can be prepared. The base steel plate according to an embodiment of the present invention is not particularly limited in its alloy composition, but preferably satisfies the composition proposed in the present invention. The above description can be equally applied to the composition of the base steel plate.

[0062] Annealing

[0063] The prepared base steel plate can be heated to a temperature range of 600 - 950 °C and annealed for 100 - 500 seconds.

[0064] In the present invention, an annealing internal oxidation method is applied during annealing, so as to form a ferrite layer through a decarburization reaction within the steel plate to improve the bendability.

[0065] During annealing, when the heating temperature is lower than 600 °C, when passing through the rollers of a continuous process production line continuously, material deformation and snake shape may occur due to work hardening. On the other hand, when the heating temperature exceeds 950 °C, due to the surface enrichment of oxygenophilic elements such as Mn, Si, Cr existing in the base steel plate and the formation of oxides, the plating property may deteriorate.

[0066] When the annealing time is less than 100 seconds, there may be a problem that the strength finally ensured after hot forming may be reduced. On the other hand, when the annealing time exceeds 500 seconds, the austenite becomes coarse, and it is difficult to obtain a steel in which martensite is finely dispersed after hot forming.

[0067] According to an embodiment of the present invention, during annealing, it can be carried out in a gas atmosphere with a dew point temperature of 5 - 20 °C, containing more than 70% of H2 and the rest being N2.

[0068] A ferrite layer can be formed by adding wet nitrogen gas into the annealing furnace. The ferrite layer can be formed as follows: water vapor contained in the wet nitrogen gas on the surface layer of the steel dissociates into O atoms, reacts with carbon in the steel, and is accompanied by a reaction of decarburization to carbon monoxide (CO), so as to form a ferrite layer through the decomposition of cementite and carbide. In addition, a small amount of H2O may be inevitably contained in the gas atmosphere.

[0069] When the dew point temperature is lower than 5 °C, the formation level of the ferrite layer is insufficient, and there may be a problem in forming an optimal ferrite layer in a short time industrially. On the other hand, when the dew point temperature exceeds 20 °C, there may be problems of corroding the equipment and aging the equipment.

[0070] Plating

[0071] The annealed base steel plate can be immersed in a plating bath for plating. By weight %, the plating bath contains Zn: 26.0 - 30.0%, Si: 6.0 - 9.0%, the balance being Al and inevitable impurities.

[0072] As described above, in the present invention, when coating is carried out such that the coating layer contains Zn: 24.0 - 27.0%, Si: 7.0 - 10.0%, the balance being Al and inevitable impurities by weight %, the composition of the plating bath can be controlled.

[0073] Zn in the coating layer forms an Al - Zn phase, thereby ensuring sacrificial corrosion protection performance. To ensure this effect, the content of Zn contained in the plating bath in the present invention can be 26.0 - 30.0%. When the Zn content in the plating bath is less than 26.0%, the Zn content in the coating layer may not reach the desired level, and as a result, there is a possibility of reducing the sacrificial corrosion protection performance. According to one embodiment of the present invention, the Zn content can be limited to 26.5% or more. On the other hand, when the Zn content in the plating bath exceeds 30.0%, there is a possibility of exceeding the Zn content range of the coating layer, and as a result, there may be a problem of generating microcracks. As one embodiment of the present invention, Zn can be contained at 29.5% or less.

[0074] In addition, during manufacturing, in order to suppress the diffusion of Al into the base iron, the Si content of the plating bath can be limited to 6.0 - 9.0%. The Si content of the plating bath affects the Si solid solution phase, so the weight % value may be a smaller value compared to the target Si content of the coating layer. When the Si content is less than 6.0%, there is a possibility of exceeding the composition range of the coating layer proposed in the present invention, and the temperature of the molten metal is higher, and the thickness of the FeAl3 and Fe2Al5 intermetallic compounds is too thick, and there may be a problem of the material being brittle. According to one embodiment of the present invention, the content of Si can be limited to 6.5% or more. On the other hand, when the Si content exceeds 9.0%, there is a possibility of exceeding the composition range proposed in the coating layer as described above. In addition, the effect of reducing the thickness of the intermetallic compound brought about by adding Si may be reduced, and there may be a problem of Si precipitation. According to one embodiment of the present invention, Si can be contained at 8.5% or less.

[0075] The temperature of the plating bath according to one embodiment of the present invention can be 580 - 680 °C.

[0076] The diffusion gradient of Al, Zn, Si in the plating bath and Fe of the base steel plate can be determined by the temperature of the plating bath, so the temperature range of the plating bath can be limited to 580 - 680 °C in the present invention.

[0077] When the temperature of the plating bath is lower than 580 °C, the diffusion of Fe in the base steel plate may be insufficient, and there is a possibility of precipitation of Al and Si. As an embodiment of the present invention, the plating bath temperature can be 600 °C or higher. As an embodiment of the present invention, the plating bath temperature can be 620 °C or higher. On the other hand, when the plating bath temperature exceeds 680 °C, due to the sharp shortening of the service life of related components such as the sleeve and bush for supporting the immersion roll used in the plating bath, vibrations occur, resulting in the suspension of production and the replacement of the immersion roll. Therefore, there may be a problem of reduced productivity.

[0078] According to an embodiment of the present invention, the coating amount during plating can be 40 - 60 g / m 2 .

[0079] During plating, when the coating amount is less than 40 g / m 2 , due to excessive diffusion of Fe after hot forming, there may be problems in use such as reduced corrosion resistance. On the other hand, during plating, when the coating amount exceeds 60 g / m 2 , the aluminum content in the coating layer relatively increases, and there may be a problem of deteriorated bendability.

[0080] Skin pass rolling

[0081] It is possible to apply 200 - 500 tons to the plated steel plate for skin pass rolling.

[0082] In the present invention, according to requirements, a step of skin pass rolling may be further included. In particular, in order to impart surface roughness and improve the surface appearance, 200 - 500 tons can be applied for skin pass rolling (skin pass mill). Detailed implementation mode

[0083] Hereinafter, the present invention will be described in more detail by way of examples. However, it should be noted that the following examples are only used to illustrate the present invention for more detailed description and are not used to limit the scope of the rights of the present invention.

[0084] (Example)

[0085] Prepare a base steel plate which, by weight percentage, contains C: 0.23%, Si: 0.25%, Mn: 1.3%, B: 0.002%, Ti: 0.03%, Cr: 0.15%, and the balance is Fe. Then, annealing and plating are carried out under the conditions shown in Table 1 below to manufacture a plated steel plate. Plating is carried out with the plating bath compositions shown in Table 1. The plating bath compositions further contain inevitable impurities in addition to the disclosed Zn, Si, and Al.

[0086] [Table 1]

[0087]

[0088] The microscopic tissue characteristics and physical properties of the manufactured coated steel sheets are shown in Table 2 below. First, in order to confirm the thickness of the ferrite layer along the thickness direction of the base steel sheet from the interface between the base steel sheet and the coating, 2-3% nitric acid ethanol etching was carried out, and then the microscopic tissue was observed through an optical microscope. The thickness of the ferrite layer measured by the above method is shown in Table 2 below. All examples contain more than 90% ferrite, and one or more of pearlite, bainite, and retained austenite were observed as the remaining tissues.

[0089] In addition, the following treatments were carried out on the manufactured coated steel sheets: dissolved in a NaOH solution for 10 minutes, then the coating was dissolved for 30 minutes using an HCl solution and an inhibitor, the two dissolved solutions were combined, and the Al, Zn, Si, and Fe component contents of the coating were measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). Based on the measured component contents, the value of relational expression 1 was calculated and recorded. Further, the position of the intersection of Zn and Al was measured and shown by the GDS analysis method.

[0090] As the physical property, using a Vickers hardness tester, the coated steel sheet was sheared and placed vertically, fixed and polished with resin, and then the hardness value (Hv) of the coating was measured with a force of 50 mN (5 g) / 10 s and shown.

[0091] Further, specimens of the coated steel sheets manufactured by the above method were collected, then cut into slabs of a specified size, and the slab specimens were heated to 900 °C in a furnace at 900 °C and held for 2 minutes. After that, the heated slab specimens were transferred to a mold within 20 seconds, and then hot forming was carried out using the mold. Then, cooling was carried out at a cooling rate of 20 °C / second to obtain a hot formed part. Samples of 35 w×100 mm were collected from the heat-treated coated steel sheets 2 for a three-point bending test. The evaluation of the bendability was carried out by setting the direction parallel to the rolling direction as the bend test axis direction, and measuring the maximum angle at which no crack occurred and showing it. Those with an angle less than 50 degrees were marked as "1", those with 50 degrees or more and less than 60 degrees were marked as "2", those with 60 degrees or more and less than 70 degrees were marked as "3", those with 70 degrees or more and less than 80 degrees were marked as "4", and those with 80 degrees or more and less than 90 degrees were marked as "5".

[0092] [Table 2]

[0093]

[0094] [Relationship 1]

[0095] R = -1.21 [Al] - 1.28 [Si] - 1.98 [Fe] - 3.17 [Zn] + 631.86

[0096] (Wherein, [Al], [Si], [Fe] and [Zn] are the weight percentages of the respective elements.)

[0097] As shown in Table 2, in the case of the inventive examples that meet the conditions of the present invention, the microstructural characteristics proposed by the present invention are met, and the physical properties desired by the present invention can also be ensured.

[0098] Figure 1 It is a photograph of observing the cross-section in the thickness direction of Inventive Example 4 of an embodiment of the present invention. The thickness of the ferrite layer can be confirmed by observing the microstructure after etching with nitric acid ethanol, as Figure 1 shown, the formed thickness is 78 μm.

[0099] Figure 2 It is a photograph of measuring Inventive Example 4 of an embodiment of the present invention by the GDS analysis method. The distributions of main elements such as Al, Zn, Si, Fe and O can be confirmed along the thickness direction of the steel plate, as Figure 2 shown, the intersection point of Zn and Al exists at a depth of 3.4 μm from the outermost surface of the coating layer along the thickness direction.

[0100] On the other hand, the comparative examples are cases where the annealing conditions or the bath composition proposed by the present invention are exceeded, and the coating layer desired by the present invention cannot be manufactured, and it is confirmed that the physical properties are also poor. In particular, in Comparative Examples 1 to 3, the intersection point of Zn and Al in the coating layer exceeds 5 μm, and excessive primary Zn phase and Zn oxide are formed on the surface layer.

[0101] The present invention has been described in detail above through examples, but other forms of examples are also allowed. Therefore, the technical idea and scope of the claims are not limited to the examples.

Claims

1. A coated steel sheet, comprising: A base steel sheet; And A coating layer formed on the base steel sheet. By weight%, the coating layer contains Zn: 24.0 - 27.0%, Si: 7.0 - 10.0%, Fe: 6.0 - 10.0%, the balance being Al and inevitable impurities. Wherein, the base steel sheet contains a ferrite layer formed along the thickness direction of the base steel sheet from the interface between the base steel sheet and the coating layer.

2. The plated steel sheet according to claim 1, wherein The R value of the coating layer defined by the following relational expression 1 is 400.0 to 500.

0. [Relational expression 1] R = -1.21 [Al] - 1.28 [Si] - 1.98 [Fe] - 3.17 [Zn] + 631.86 In the formula, [Al], [Si], [Fe], and [Zn] are the weight percentages of each element.

3. The plated steel sheet according to claim 1, wherein, When analyzed by a glow discharge spectrometer (GDS), the intersection point of Zn and Al in the coating layer exists within a depth of 5.0 μm along the thickness direction from the outermost surface of the coating layer.

4. The plated steel sheet according to claim 1, wherein, The thickness of the ferrite layer is 70 - 80 μm.

5. The coated steel sheet according to claim 1, wherein, The coating amount is 40 - 60 g / m 2 .

6. The plated steel sheet according to claim 1, wherein, The hardness of the coated steel sheet is 400 - 500 Hv.

7. The plated steel sheet according to claim 1, wherein, When the coated steel sheet is subjected to a bending test after hot forming, the maximum bending angle is 70 degrees or more.

8. The plated steel sheet according to claim 1, wherein, By weight%, the base steel sheet contains 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, B: 0.0001 - 0.01%, the balance being Fe and impurities.

9. The plated steel sheet according to claim 8, wherein, By weight%, the base steel sheet further contains one or more selected from Ti: 0.1% or less, Cu: 1.00% or less, Mo: 1.00% or less, Cr: 1.00% or less, Ni: 1.00% or less, V: 1.00% or less, Ca: 0.01% or less, Nb: 0.1% or less, Sn: 1% or less, W: 1% or less, Sb: 1% or less, Mg: 0.1% or less, Co: 1% or less, As: 1% or less, Zr: 1% or less, Bi: 1% or less, REM: 0.3% or less.

10. A method for manufacturing a coated steel sheet, comprising the following steps: Preparing a base steel sheet; Heating the prepared base steel sheet to a temperature range of 600 - 950 °C and annealing it at a dew point temperature of 5 - 20 °C; And Immersing the annealed base steel sheet in a plating bath for plating. By weight%, the plating bath contains Zn: 26.0 - 30.0%, Si: 6.0 - 9.0%, the balance being Al and inevitable impurities.

11. The manufacturing method of the plated steel sheet according to claim 10, wherein, The annealing step is maintained for 100 - 500 seconds in a gas atmosphere containing 70% or more of H2 and the balance being N2.

12. The method for manufacturing a plated steel sheet according to claim 10, wherein, The temperature of the plating bath is 580 - 680 °C.

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