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 heat resistance and sacrificial corrosion resistance, and a method for manufacturing the same.

Description

Technical Field

[0001] The present invention relates to a coated steel sheet and a method for manufacturing the same, and more particularly, to a coated steel sheet having excellent heat resistance and sacrificial corrosion resistance and a method for manufacturing the same. Background Art

[0002] Steel for automotive exhaust systems needs to satisfy heat resistance and corrosion resistance. When using a conventional galvanized steel sheet, the melting point of the coating is low, so when discharging high-temperature exhaust gas, there is a problem that the coating undergoes alloying and discoloration. In addition, when using an aluminized coating, it does not have sacrificial corrosion resistance. Therefore, when the coating is damaged during vehicle operation, carbon steel may corrode, so there is a problem that expensive stainless steel must be used.

[0003] To solve the above problems, Patent Document 1 proposes a method in which a zinc foil is pressed onto the surface of a cold-rolled steel sheet by a composite method, and an aluminum foil is pressed onto the zinc foil, and then it is passed through an oven in a temperature range of 300 - 400 °C for manufacturing. However, this method has the advantage of ensuring corrosion resistance and heat resistance, but the fixing is relatively complicated, so it is difficult to apply in practice.

[0004] Patent Document 2 proposes an aluminized steel sheet having excellent heat resistance and discoloration resistance by forming a coating containing Al and Si on carbon steel. The problem with this technology is that the coating is composed of aluminum, and the surface corrosion resistance is excellent, but it does not have sacrificial corrosion resistance, so it cannot effectively prevent the corrosion of the base material iron.

[0005] Patent Document 3 proposes a ferritic stainless steel for aluminized steel sheets, which has excellent condensate corrosion resistance and high-temperature oxidation resistance due to the use of high-sulfur fuel. However, since expensive stainless steel is used as the base material iron, there is also a problem of increased cost.

[0006] [Prior Art Documents]

[0007] [Patent Documents]

[0008] (Patent Document 1) Korean Patent Publication No. 10-0580047

[0009] (Patent Document 2) Korean Patent Publication No. 10-1197955

[0010] (Patent Document 3) Korean Patent Publication No. 10-1485643 Summary of the Invention

[0011] (I) Technical Problems to be Solved

[0012] According to an embodiment of the present invention, an object is to provide a coated steel sheet and a method for manufacturing the same.

[0013] According to an embodiment of the present invention, an object is to provide a plated steel sheet having excellent heat resistance and sacrificial corrosion resistance and a method for manufacturing the same.

[0014] The technical problems of the present invention are not limited to the above. Those skilled in the art to which the present invention pertains can easily understand the additional technical problems of the present invention based on the entire text of the specification of the present invention.

[0015] (II) Technical solution

[0016] According to an embodiment of the present invention, a plated steel sheet can be provided, the plated steel sheet including: a base steel sheet; and a plating layer formed on the base steel sheet, and in terms of weight%, the plating layer contains: Zn: 15 - 35%, Si: 5.0 - 15.0%, Fe: 1.0 - 7.0%, the balance being Al and other impurities,

[0017] in terms of weight%, other impurities in the plating layer are 5.0% or less,

[0018] The ratio of the content of Si in the region from the surface to the 1 / 3 position of the plating layer in the thickness direction to the content of Si in the entire region of the plating layer is 60 - 85%.

[0019] In terms of weight%, the base steel sheet may contain: C: 0.1% or less, Mn: 2.5% or less, Ti: 0.1% or less, Nb: 0.1% or less, Si: 1.5% or less, Al: 0.5% or less, P: 0.01% or less, S: 0.01% or less, the balance being Fe and other inevitable impurities.

[0020] The difference in whiteness (ΔL) before and after exposure of the plated steel sheet after being exposed at 500 °C for 24 hours can be 5 or less, and the ratio of the occurrence of cross-sectional red rust after 200 hours of salt spray can be 5% or less.

[0021] According to an embodiment of the present invention, a method for manufacturing a plated steel sheet can be provided, the manufacturing method including the following steps: preparing a base steel sheet; performing heat treatment on the base steel sheet; immersing the heat-treated base steel sheet in a plating bath for plating, and in terms of weight%, the plating bath contains: Zn: 17 - 38%, Si: 7 - 18%, the balance being Al and other impurities; and cooling the plated steel sheet at an average cooling rate of 10 - 50 °C / second to a temperature range below 300 °C, wherein, in terms of weight%, other impurities in the plating bath are 6.0% or less.

[0022] The base steel plate may contain, by weight %: C: 0.1% or less, Mn: 2.5% or less, Ti: 0.1% or less, Nb: 0.1% or less, Si: 1.5% or less, Al: 0.5% or less, P: 0.01% or less, S: 0.01% or less, the balance being Fe and other inevitable impurities.

[0023] During the heat treatment, the base steel plate may be held in the temperature range of 750 - 850 °C for 50 - 500 seconds.

[0024] The temperature of the plating bath may be 40 °C or more higher than the melting point of the plating composition system.

[0025] (III) Advantageous Effects

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

[0027] According to one embodiment of the present invention, a plated steel plate having excellent heat resistance and sacrificial corrosion resistance and a method for manufacturing the same can be provided.

[0028] According to one embodiment of the present invention, an aluminum-based plated steel plate that can be used for an automotive exhaust system (muffler) and a method for manufacturing the same can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Photograph showing the occurrence of red rust in Invention Example 5 according to one embodiment of the present invention.

[0030] Figure 2 Photograph showing the Si distribution in Invention Example 5 according to one embodiment of the present invention taken by EPMA.

[0031] Figure 3 Photograph showing the occurrence of red rust in Comparative Example 7 deviating from one embodiment of the present invention.

[0032] Figure 4 Photograph showing the Si distribution in Comparative Example 7 deviating from one embodiment of the present invention taken by EPMA. DETAILED DESCRIPTION OF THE INVENTION

[0033] Preferred specific embodiments of the present invention will be described below. The specific embodiments of the present invention can be deformed 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 skilled in the art.

[0034] In the present invention, by enabling sacrificial corrosion resistance and heat resistance, which are not possessed by aluminized steel sheets using existing stainless steel as a material, to be applied to carbon steel, it was confirmed that a coated steel sheet that is inexpensive and has excellent heat resistance and sacrificial corrosion resistance can be provided, thus completing the present invention.

[0035] Hereinafter, the present invention will be described in detail.

[0036] According to an embodiment of the present invention, the coated steel sheet may include: a base steel sheet; and a coating layer formed on the base steel sheet.

[0037] Unless otherwise specifically stated, the % representing the content of each element in the present invention is based on weight.

[0038] Base steel sheet

[0039] In the present invention, the composition of the base steel sheet is not particularly limited. However, according to an embodiment of the present invention, by weight %, the base steel sheet may have the following composition: C: 0.1% or less, Mn: 2.5% or less, Ti: 0.1% or less, Nb: 0.1% or less, Si: 1.5% or less, Al: 0.5% or less, P: 0.01% or less, S: 0.01% or less.

[0040] In addition to the above composition, the steel material of the present invention may include the balance of iron (Fe) and inevitable impurities. Inevitable impurities may be inadvertently mixed in during the normal manufacturing process, so these impurities cannot be excluded. Such impurities are well known to those skilled in the art of ordinary steel manufacturing, so all of their contents are not particularly mentioned in this specification.

[0041] Coating layer

[0042] According to an embodiment of the present invention, by weight %, the coating layer contains: Zn: 15 - 35%, Si: 5.0 - 15.0%, Fe: 1.0 - 7.0%, the balance of Al and other impurities, and the other impurities may be 5.0% or less.

[0043] When the content of Zn in the coating layer exceeds 35%, there may be a problem of poor coating adhesion. As an embodiment of the present invention, the content of Zn may be 30% or less. On the other hand, when the content of Zn is less than 15%, there is a problem that sacrificial corrosion resistance cannot be sufficiently ensured. As an embodiment of the present invention, the content of Zn may be 20% or more.

[0044] When plating with Al, the advantage of adding Si is that it can suppress the excessive reaction between Al and Fe to ensure plating adhesion. When the Si content exceeds 15.0%, the plating adhesion may deteriorate instead. As an embodiment of the present invention, the Si content can be 120% or less. On the other hand, in order to effectively ensure the above advantages, the Si content can be limited to 5.0% or more. As an embodiment of the present invention, the Si content can be 7.0% or more.

[0045] For Fe, although it is not artificially added during plating, the Fe component of the base steel plate reacts with the Al in the coating, and an Al-Fe alloy phase can be formed in the direction of the coating side at the interface between the coating and the base steel plate. When the Fe content in the coating is less than 1.0%, the Al-Fe alloy phase is insufficient, and the plating adhesion may deteriorate. On the other hand, when the Fe content in the coating exceeds 7.0%, an excessive amount of Al-Fe alloy phase is formed, and during processing, there may be a problem of coating peeling.

[0046] In addition, the content of other impurities can be 5.0% or less. Impurities can include Mg, Mn, etc. When the Mg content exceeds 5.0%, Mg oxide is formed on the surface of the plating bath during plating, which may cause surface defects and may change color at high temperatures.

[0047] According to an embodiment of the present invention, the plating amount based on one side can be 20 - 200 g / m 2 。

[0048] According to an embodiment of the present invention, the ratio of the Si content in the region from the surface to the 1 / 3 position along the thickness direction of the coating to the Si content in the entire region of the coating can be 60 - 85%.

[0049] The distribution of Si and Si compounds in the coating has a significant impact on corrosion resistance. In particular, the more Si and Si compounds are distributed on the surface of the plated steel sheet, the more beneficial it is to ensure corrosion resistance. In the present invention, an electron probe micro analyzer (EPMA) can be used to analyze the cross-section of the steel sheet to confirm the Si distribution.

[0050] When the ratio of the Si content in the region from the surface to the 1 / 3 position along the thickness direction of the coating to the Si content in the entire region of the coating is less than 60%, it may be difficult to ensure the desired corrosion resistance. On the other hand, when the above ratio exceeds 85%, too much Si is distributed on the surface, so the surface quality of the coating may deteriorate.

[0051] Hereinafter, the manufacturing method of the steel sheet of the present invention will be described in detail.

[0052] According to an embodiment of the present invention, the plated steel sheet can be manufactured by heat-treating, plating, and cooling a base steel sheet that satisfies the alloy composition of the present invention.

[0053] Preparation of the base steel sheet

[0054] According to an embodiment of the present invention, a base steel sheet that satisfies the alloy composition can be prepared. There is no particular limitation on the alloy composition of the base steel sheet according to an embodiment of the present invention, and it is more preferably to satisfy the composition proposed by the present invention.

[0055] The composition of the base steel sheet can apply the same content as described above.

[0056] Heat treatment

[0057] In the present invention, heat treatment can be performed before plating. The heat treatment conditions are not particularly limited, but conventional conditions that can be used in the same technical field can be applied. According to an embodiment of the present invention, the base steel sheet can be heat-treated in the temperature range of 750 - 850 °C for 50 - 500 seconds.

[0058] Plating

[0059] The heat-treated base steel sheet can be immersed in a plating bath for plating. The plating bath contains, by weight%: Zn: 17 - 38%, Si: 7 - 18%, and the balance of Al and other impurities.

[0060] When the content of Zn in the plating bath exceeds 38%, a large amount of ash is generated in the plating bath during plating, so there may be problems such as the generation of dust, which may reduce the workability. In addition, the Zn content of the coating layer exceeding the desired value of the present invention may occur. As an embodiment of the present invention, the Zn content can be 37% or less. On the other hand, when the Zn content is less than 17%, the desired Zn content of the coating layer cannot be ensured, and there is a problem that the sacrificial corrosion resistance cannot be sufficiently ensured. As an embodiment of the present invention, the Zn content can be 20% or more.

[0061] When plating Al, the advantage of adding Si is that it can suppress the excessive reaction of Al and Fe to ensure the plating adhesion. When the Si content exceeds 18%, the melting point temperature of the plating bath rises during plating, and there may be a problem of reduced durability of the structure in the plating bath. As an embodiment of the present invention, the Si content can be 16% or less. On the other hand, in order to effectively ensure the above advantages, the Si content can be limited to 7% or more. As an embodiment of the present invention, the Si content can be 9% or more.

[0062] For Fe, it is not artificially added to the plating bath. However, the steel sheet reacts with Al in the coating, and an Al-Fe alloy phase can be formed toward the coating direction at the interface between the base steel sheet and the coating, thus being included in the coating. In addition, during plating, the steel sheet is immersed in the plating bath in the manufacturing process, and the Fe component of the steel sheet can dissolve in the plating bath. That is, although Fe is not specifically added to the plating bath, a certain level of amount will inevitably be included.

[0063] In addition, the content of other impurities can be 6.0% or less. As impurities, Mg, Mn, etc. can be included. When the content of Mg exceeds 6.0%, Mg oxide is formed on the surface of the plating bath during plating, which may cause surface defects and may change color at high temperatures.

[0064] According to an embodiment of the present invention, the plating amount based on one side can be 20 - 200 g / m 2 .

[0065] Cooling

[0066] The plated steel sheet can be cooled to a temperature range below 300°C at an average cooling rate of 10 - 50°C / second.

[0067] In the present invention, by enriching Si on the surface layer of the coating, a dense corrosion product is formed during corrosion, and in order to improve the corrosion resistance, the cooling rate can be restricted. The lower the cooling rate, the more Si and Si compounds can move to the surface layer part, and in the present invention, its distribution can be restricted.

[0068] When the average cooling rate is less than 10°C / second, Si enrichments are formed inside the coating, and galvanic corrosion is promoted in the coating, thus the corrosion resistance can be reduced. In addition, since the coating is not sufficiently cooled, part of the coating may fall off. On the other hand, when the cooling rate exceeds 50°C / second, the coating is cooled too quickly, inhibiting the movement of Si and Si oxides to the surface layer, and thus there may be a problem of poor corrosion resistance.

[0069] In the present invention, the cooling termination temperature can refer to the temperature reached by the top roll. During cooling, when the temperature of the steel sheet exceeds 300°C before reaching the top roll, there may be a problem of plating peeling in the top roll.

[0070] The plated steel sheet of the present invention can ensure excellent characteristics of heat resistance, sacrificial corrosion protection, and plating adhesion. Detailed Description of the Invention

[0071] 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.

[0072] (Examples)

[0073] A base steel plate with a composition of C: 0.01%, Mn: 0.5%, Ti: 0.01%, Nb: 0.01%, Si: 0.3%, Al: 0.045%, P: 0.01%, and S: 0.01% by weight is heat-treated and then plated under the conditions shown in Table 1 below to produce a plated steel plate. Herein, the cooling temperature specifically may refer to the upper roll arrival temperature. Additionally, as shown in the plating bath composition of Table 1, although Fe is not intentionally added to the plating bath, during the manufacturing process, Fe of the steel plate dissolves while the steel plate is immersed in the plating bath and is contained at a corresponding weight percentage level. As other components, unavoidable impurities other than Zn, Si, and Fe may be included, and the balance is Al.

[0074] In the present invention, as the heat treatment conditions, heat treatment is carried out at a temperature of 800 °C for 50 seconds in a furnace maintaining a reducing atmosphere, and then it is immersed in the plating bath. The immersion temperature is maintained at the same temperature as the plating bath temperature, and the plating bath temperature is maintained at a temperature 40 °C higher than the melting point of the entire plating composition system. The plating amount is constantly applied at 60 g / m² on a single-sided basis using air wiping. 2 。

[0075] [Table 1]

[0076]

[0077] For the obtained plated steel plate, the composition and Si ratio of the plating layer are shown. The composition of the plating layer is shown using Inductively Coupled Plasma (ICP), and the Si ratio is analyzed on the cross-section of the steel plate using an Electron Probe Micro Analyzer (EPMA) and the ratio of Si and Si compounds is shown. Herein, the surface part refers to the region from the plating layer surface to the position 1 / 3 of the plating layer thickness direction, and the interior refers to the remaining region of the plating layer other than the surface part.

[0078] In addition, for heat resistance, sacrificial corrosion protection, plating adhesion, and roll marks, the physical properties are observed and shown. The measurement criteria and methods for each physical property are as follows.

[0079] ○ Heat resistance: The plated test piece is exposed in an oven at 500 °C for 24 hours, the difference in whiteness (ΔL) before and after exposure is measured, and evaluation is carried out according to the following criteria. The whiteness is measured according to ISO 2469.

[0080] O: Δ5 or less

[0081] X: Exceeding Δ5

[0082] ○ Sacrificial corrosion resistance: Install the plated test piece so that the cross-section is exposed, then conduct a 200-hour salt spray test, and then observe whether red rust occurs on the surface. Among them, the salt spray test can be carried out by spraying a 5% NaCl solution at 35 °C, and the degree of red rust occurrence is observed visually.

[0083] O: The cross-section red rust occurrence ratio is 5% or less

[0084] X: The cross-section red rust occurrence ratio exceeds 5%

[0085] ○ Plating adhesion: After the 0-t bending experiment, observe whether there is a peeled plating layer through the tape experiment. Among them, in the tape experiment, after bending, it is straightened again, and then the tape is pasted at the bent position and then removed again, so as to observe whether the plating layer adheres to the tape.

[0086] O: No plating layer peeling occurs

[0087] X: Plating layer peeling occurs

[0088] ○ Roller marks: When the steel plate from the plating bath passes through the upper roller, observe whether the plating layer adheres to the surface of the upper roller.

[0089] O: No adhesion occurs

[0090] X: Adhesion occurs

[0091] [Table 2]

[0092]

[0093] As shown in Table 1, in the case of the inventive examples that meet the conditions of the present invention, it was confirmed that all the physical properties desired by the present invention could be ensured.

[0094] Figure 1 Shows a photograph of the occurrence of red rust in Inventive Example 5 according to an embodiment of the present invention. As Figure 1 shown, when conducting the experiment on whether red rust occurs, it can be confirmed that no red rust occurs. Figure 2 Shows a photograph of the Si distribution of Inventive Example 5 according to an embodiment of the present invention taken by EPMA. As Figure 2 shown, it can be confirmed that a large amount of Si distribution is observed in the surface part of the plating layer.

[0095] On the other hand, Comparative Examples 1 to 11 are examples that do not meet the plating bath composition proposed by the present invention. During plating, the plating bath composition cannot fully meet the range proposed by the present invention, and when manufacturing the plated steel sheet, the composition of the plating layer deviates from the range of the present invention. As a result, all the physical properties desired by the present invention cannot be ensured.

[0096] Figure 3Photographs showing red rust formation in Comparative Example 7, which deviates from an embodiment of the present invention. As Figure 3 shown, it can be confirmed that red rust has occurred.

[0097] Figure 4 Photographs showing the Si distribution in Comparative Example 7, which deviates from an embodiment of the present invention, taken by EPMA. As Figure 4 shown, it can be confirmed that there is a greater distribution of Si inside compared to the coating surface.

[0098] Comparative Example 12 and Comparative Example 13 are examples where the cooling rate deviates from the range proposed by the present invention during cooling after plating. In Comparative Example 12, the cooling rate was not achieved, and Si diffused excessively from the steel plate surface. As a result, when passing through the upper roll, there was a problem of adsorbed coating. In Comparative Example 13, the cooling rate was too fast, and the surface Si diffusion was insufficient. As a result, the sacrificial corrosion resistance deteriorated.

[0099] As described above, the present invention has been described in detail by way of examples, but other forms of examples may also be included. 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: 15 - 35%, Si: 5.0 - 15.0%, Fe: 1.0 - 7.0%, the balance being Al and other impurities, By weight%, the other impurities in the coating layer are 5.0% or less, The ratio of the content of Si in the region from the surface to the 1 / 3 position of the coating layer in the thickness direction to the content of Si in the entire region of the coating layer is 60 - 85%.

2. The coated steel sheet according to claim 1, wherein, By weight%, the base steel sheet contains: C: 0.1% or less, Mn: 2.5% or less, Ti: 0.1% or less, Nb: 0.1% or less, Si: 1.5% or less, Al: 0.5% or less, P: 0.01% or less, S: 0.01% or less, the balance being Fe and other inevitable impurities.

3. The plated steel sheet according to claim 1, wherein, The difference in whiteness (ΔL) before and after the coated steel sheet is exposed at 500 °C for 24 hours is 5 or less, and the cross-sectional red rust occurrence ratio after 200 hours of salt spray is 5% or less.

4. A method for manufacturing a coated steel sheet, comprising the following steps: Preparing a base steel sheet; Heat-treating the base steel sheet; Immersing the heat-treated base steel sheet in a plating bath for plating, by weight%, the plating bath contains: Zn: 17 - 38%, Si: 7 - 18%, the balance being Al and other impurities; and Cooling the plated steel sheet to a temperature range below 300 °C at an average cooling rate of 10 - 50 °C / second, Wherein, by weight%, the other impurities in the plating bath are 6.0% or less.

5. The manufacturing method of the plated steel sheet according to claim 4, wherein, By weight%, the base steel sheet contains: C: 0.1% or less, Mn: 2.5% or less, Ti: 0.1% or less, Nb: 0.1% or less, Si: 1.5% or less, Al: 0.5% or less, P: 0.01% or less, S: 0.01% or less, the balance being Fe and other inevitable impurities.

6. The manufacturing method of the steel plate according to claim 4, wherein During the heat treatment, the base steel sheet is held in the temperature range of 750 - 850 °C for 50 - 500 seconds.

7. The manufacturing method of the plated steel sheet according to claim 4, wherein, The temperature of the plating bath is 40 °C or more higher than the melting point of the plating composition system.

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