Hot-dip galvanized steel sheet with excellent corrosion resistance and workability, and method for manufacturing the same.

Abstract

Regarding plated steel sheets applicable for various purposes such as building materials, home appliances, and automobiles, more specifically, we provide hot-dip galvanized steel sheets with excellent corrosion resistance and workability, as well as a method for manufacturing the same. [Solution] A hot-dip galvanized steel sheet is provided, comprising a base steel sheet and a Zn-Al-Mg alloy plating layer on at least one surface of the base steel sheet, wherein the Zn-Al-Mg alloy plating layer contains, by weight %, aluminum (Al): 20-30%, magnesium (Mg): 3-5%, the remainder being Zn and other unavoidable impurities, the surface structure of the Zn-Al-Mg alloy plating layer is composed of a Zn phase, a Zn-Al phase, a MgZn2 phase and a Zn-Al-MgZn2 phase, and the internal structure includes an Fe-Al alloy phase, thereby providing a hot-dip galvanized steel sheet with excellent corrosion resistance and workability.

Description

Technical Field

[0001] The present invention relates to a plating applicable for various purposes such as for building materials, home appliances, automobiles, etc. and more particularly to a hot-dip plated steel sheet excellent in corrosion resistance and workability and a method for producing the same.

Background Art

[0002] The process of plating a steel sheet by a continuous hot-dip plating process not only has a lower production cost compared to processes such as electroplating and dry plating, but can also ensure excellent quality. Therefore, its range of use as a material for building, ships, home appliances, inner and outer panels of automobiles, etc. is expanding. On the other hand, in recent years, due to the rapid increase in the price of raw materials containing zinc, new plating systems with a small plating adhesion amount but excellent corrosion resistance have been actively developed as an alternative to conventional zinc-plated steel sheets. In this regard, alloy-plated steel sheets that add aluminum and magnesium to the conventional zinc plating system and have excellent corrosion resistance even with a small adhesion amount have emerged.

[0003]

[0004]

[0005]

[0006]

[0006] Conventionally, zinc-aluminum-magnesium alloy plated steel sheets developed mainly in Japan ( Patent Documents 1 and 2) tend to oxidize unevenly and discolor when an aluminum and magnesium structure that is easy to oxidize develops on the surface of the steel sheet, and the surface becomes dark over time. ​The surface quality deteriorates significantly as it changes. To improve this problem, high-grade alloying elements are used. There is a method of adding it to the plating bath, but this increases costs and by-reaction products in the plating bath. It has the disadvantage of causing problems such as an increase in the number of cases.

[0007] Zinc-aluminum-magnesium alloy plating, recently developed mainly in Europe. The steel plate (Patent Document 3) was set with the ultimate goal of being applied to automobiles, and aluminum The total amount of nium and magnesium added is the same as that of zinc-aluminum-magnesium developed in Japan. Because it contains less of the alloy-plated steel sheet, there is a problem in that sufficient corrosion resistance cannot be ensured. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 1999-140615 [Patent Document 2] Japanese Patent Publication No. 2000-104154 [Patent Document 3] European Published Patent 1621645A1 [Overview of the project] [Problems that the invention aims to solve]

[0009] One aspect of the present invention is to optimize the composition of the alloy plating system and the cooling process of the plated steel material. By optimizing it, it not only has high corrosion resistance but also a good surface appearance and excellent processability. The objective is to provide hot-dip galvanized steel sheets and methods for manufacturing the same.

[0010] The problems that the present invention will address are not limited to those described above. Additional problems that the present invention will address are covered herein. The invention is described in general terms, and any person with ordinary skill in the art to which the present invention belongs would understand it. 、There is no difficulty in understanding any additional problems of the present invention from the content described in the specification of the present invention. None.

Means for Solving the Problems

[0011] One aspect of the present invention is a hot-dip galvanized steel sheet including a base steel sheet and a Zn-Al-Mg-based alloy plating layer on at least one surface of the base steel sheet, wherein the Zn-Al-Mg-based alloy plating layer contains, by weight%, aluminum (Al): 20 to 3 0%, magnesium (Mg): 3 to 5%, and the balance being Zn and other inevitable impurities, and the surface structure of the Zn-Al-Mg-based alloy plating layer is composed of a Zn phase, a Zn-Al phase, a MgZn2 phase and a Zn-Al-MgZn2 phase, and the internal structure contains an Fe-Al alloy phase, to provide a hot-dip galvanized steel sheet excellent in corrosion resistance and workability.

[0012] Another aspect of the present invention is to prepare an alloy plating bath containing, by weight%, aluminum (Al): 20 to 30%, magnesium (Mg): 3 to 5%, and the balance being Zn and other inevitable impurities, immersing a base steel sheet in the alloy plating bath to perform plating to produce a plated steel sheet, and cooling the plated steel sheet at a cooling rate of 8 to 30 °C / s, wherein the plating is performed by adjusting the draw-in temperature of the plating bath to 500 to 550 °C and the temperature of the plating bath to 480 to 550 °C and passing through a plating tank, to provide a manufacturing method of a hot-dip galvanized steel sheet excellent in corrosion resistance and workability.

Effects of the Invention

[0013] According to the present invention, by forming the cross-sectional structure of the alloy plating layer finely and uniformly and improving the adhesion of the alloy plating layer, the corrosion resistance can be improved, and a good surface An alloy-plated steel sheet having excellent surface quality and workability can be provided.

Brief Description of the Drawings

[0014] [Figure 1] The photograph shows the plating appearance of the plated steel sheet according to an embodiment of the present invention. [Figure 2] The photograph shows the cross-section of the alloy plating layer of the plated steel sheet in FIG. 1 above observed by SEM. [Figure 3] The photograph shows the microstructure in the alloy plating layer of Comparative Example 1 (left) and Inventive Example 2 (right) according to an embodiment of the present invention observed by SEM.

Modes for Carrying Out the Invention

[0015] When performing Zn-Al-Mg alloy plating to obtain a Zn-Al-Mg alloy-plated steel sheet the start of solidification of the alloy plating layer is determined by the contents of aluminum and magnesium and at the end of solidification, finally, the eutectic phase containing Zn-Al-Mg solidifies while the solidification reaction of the plating layer ends. However, before the end of solidification of the ternary eutectic structure of Zn-Al-Mg surface defects such as flow marks are likely to occur due to the strong oxidizing property of Mg, so there are restrictions on the use of Mg.

[0016] Nevertheless, in order to improve the corrosion resistance of the Zn-Al-Mg alloy-plated steel sheet it is essential to add Mg in an amount of a certain level or more, and it was confirmed that as the content of such Mg increases, the problem that the flow mark defects due to oxidation become larger. Therefore, the present inventors intensively studied a method that can ensure good surface quality while ensuring the corrosion resistance by Mg in an amount of a certain level or more.

[0017] Specifically, Zn-Al-Mg alloy plating systems exhibit strong erosive properties in the plating bath, and solidification occurs. We confirmed that the solid interval is wide, and together with the alloy composition of the Zn-Al-Mg alloy plating system, we investigated the cold We attempted to control the microstructure of the alloy plating layer by optimizing the processing steps.

[0018] As a result, Zn-A exhibits excellent corrosion resistance, good surface quality, and superior processability. We confirmed that l-Mg alloy plated steel sheets can be provided, and thus completed the present invention.

[0019] The present invention will be described in detail below.

[0020] A hot-dip galvanized steel sheet according to one aspect of the present invention comprises a base steel sheet and at least one surface of the base steel sheet. The material comprises a Zn-Al-Mg alloy plating layer, and the Zn-Al-Mg alloy plating layer is In weight percent, aluminum (Al): 20-30%, magnesium (Mg): 3-5% The remainder may contain Zn and other unavoidable impurities.

[0021] The above Zn-Al-Mg alloy plating layer has the alloy composition described above, with Al, Mg and Zn It can be formed from an alloy plating bath containing the alloy.

[0022] Specifically, Al in the above alloy plating bath is the main element that ensures the high corrosion resistance of hot-dip galvanized steel sheets. If it is a primary element and its content is less than 20%, then the Zn-Al-Mg alloy plating layer is It is difficult to ensure sufficient corrosion resistance. In contrast, when its content exceeds 30% This leads to an increase in dross formation during plating, resulting in a deterioration of the surface quality of the final product. ru.

[0023] The Mg in the above alloy plating bath is used to improve the corrosion resistance of the alloy plating layer and the cut surface of the plating layer. It is an element added to the material, and if its content is less than 3%, the effect on improving corrosion resistance is minimal. Yes, but if its content exceeds 5%, dross generation occurs due to oxidation of the plating bath. There is a problem in that it increases significantly.

[0024] The above Al and Mg are both elements that improve the corrosion resistance of the plating layer, and these elements As the sum of increases, corrosion resistance can be further improved, therefore, in the present invention, The total amount of Al and Mg can be limited to 25% or more.

[0025] On the other hand, the composition in the alloy plating bath is substantially the same as the composition in the alloy plating layer.

[0026] The Zn-Al-Mg alloy plating layer having the above alloy composition has a fine and uniform structure. It can have, specifically, the surface structure of the Zn-Al-Mg alloy plating layer is Z It consists of n phase, Zn-Al phase, MgZn2 phase and Zn-Al-MgZn2 phase, and internal assembly The weave preferably contains an Fe-Al alloy phase.

[0027] The present invention provides a plating structure for the Zn-Al-Mg alloy plating layer, which is fine Zn-Al-Mg alloy. l-phase, MgZn2 phase, and Zn-Al-MgZn2 phase are formed on the surface (surface layer) of the alloy plating layer. By doing so, corrosion resistance can be improved.

[0028] Furthermore, this invention relates to the interface of conventional Zn-Al-Mg alloy plated steel sheets (base steel sheet and plating layer). The Fe-Al intermetallic compound (Fe-Al alloy phase) formed at the interface is used in the alloy plating layer. By ensuring uniform formation within the internal structure, it has the effect of securing a good surface appearance. ru.

[0029] On the other hand, the above Zn-Al-Mg alloy plating layer can have a thickness of 3 to 40 μm. The surface structure within the Zn-Al-Mg alloy plating layer is the same as the surface of the alloy plating layer. From 1 / 3t to 1 / 2t in the thickness direction (where t represents the thickness of the alloy plating layer (μm)) This corresponds to the area up to the aforementioned region, and the remaining area after excluding the surface tissue corresponding to the aforementioned region is called the internal tissue. It is possible.

[0030] The hot-dip galvanized steel sheet of the present invention has a surface structure and an internal structure of a Zn-Al-Mg alloy plating layer. By forming the surface tissue in a different manner, the conventional solution is formed as described above. It has significantly superior corrosion resistance compared to hot-dip galvanized steel sheets, and also boasts a beautiful surface appearance. There are advantages.

[0031] The following describes another aspect of the present invention: manufacturing a hot-dip galvanized steel sheet with excellent corrosion resistance and workability. I will explain the method in detail.

[0032] The present invention relates to a method for manufacturing a hot-dip galvanized steel sheet with excellent corrosion resistance and workability, comprising the above-mentioned alloy composition The steps involve preparing an alloy plating bath and immersing a base steel sheet in the alloy plating bath to perform the plating. The process may include the steps of manufacturing a plated steel sheet and cooling the plated steel sheet. Cut.

[0033] Plating is performed by immersing a base steel sheet in an alloy plating bath that satisfies the alloy composition proposed in this invention. In this process, the inlet temperature of the plating bath should be 500-550°C, and the temperature of the plating bath should be 480-550°C. It is preferable to adjust the settings and pass the mixture through the plating bath.

[0034] If the entry temperature of the above plating bath is less than 500°C, the surface of the formed alloy plating layer Unplated areas occur on the surface, or the adhesion of the plating layer deteriorates, and in response to this, temperatures exceeding 550°C In such cases, there is a problem in that the adhesion of the plating layer decreases.

[0035] It is preferable to cool the plated steel sheet obtained by plating as described above, and the cooling is performed in 8 It is preferable to cool the temperature down to 300°C or below at a cooling rate of ~30°C / s.

[0036] If the cooling rate is less than 8°C / s during the above cooling process, the plating layer will not solidify uniformly. In contrast, when the cooling rate exceeds 30°C / s, flow-type fringe defects appear on the surface of the plating layer. There is a problem in that this occurs.

[0037] Furthermore, the above cooling uses 4% or less by volume (including 0%) of hydrogen (H2) and the remainder as nitrogen (N2). This can be done in a gas atmosphere composed of air jet coolers, for example. A jet cooler can be used.

[0038] By controlling the cooling process in this way, the primary Zn phase and Zn-Al are formed on the surface of the alloy plating layer. First, the phase is generated, and the lower region of the surface (the region between the surface and the internal alloy layer (internal structure)) is intended to be generated. To achieve the desired taste, fine Zn-Al phase, MgZn2 phase, and Zn-Al-MgZn2 phase are used. It can be formed.

[0039] Ultimately, a uniform structure is formed on the surface of the alloy plating layer, improving the corrosion resistance of the flat surface. This is significantly improved, and in particular, the sacrificial corrosion protection of the cross-section is improved by the Zn phase and MgZn2 phase. You can obtain results.

[0040] The step of gas wiping the plated steel sheet before cooling it may further be included. The amount of plating can be adjusted by the gas wiping treatment described above.

[0041] The gas used during the above gas wiping process can be air or nitrogen. Of these, the use of nitrogen is more preferable. This is because when air is used, the plating layer This is because Mg may preferentially oxidize on the surface, potentially inducing surface defects in the plating layer. .

[0042] On the other hand, the above-mentioned base steel sheet may be ordinary carbon steel (including low-carbon steel), stainless steel, etc. Cold-rolled materials are an example, but the term is not particularly limited.

[0043] The above cold-rolled material undergoes a degreasing process to wash the rolling oil off the surface of the rolled steel sheet, and then the rolling assembly... The fabric may have undergone annealing heat treatment to restore the weave and ensure the quality of the material.

[0044] The above annealing heat treatment can be carried out in a temperature range of 700 to 850°C, but generally, low carbon If it is raw steel, annealing heat treatment is performed in the temperature range of 700-800°C, and ultra-low carbon steel or For high-strength steel, annealing heat treatment can be performed at 800-850°C.

[0045] The above cold-rolled material may have a thickness of 0.3 to 1 mm, but is not limited to this. It's not something that can be done. [Examples]

[0046] The present invention will be described in more detail below with reference to examples. However, the following examples are based on the present invention. This is merely an example to illustrate and explain in more detail, and is not intended to limit the scope of the rights of the present invention. It is important to note that this is not the case. The scope of the rights of this invention is described in the claims. It is determined by the matters concerned and by matters that can be reasonably inferred from them.

[0047] (Example 1) Cold-rolled low-carbon steel (0.003% C - 0.15% Mn - remainder Fe and others) After degreasing a test specimen (0.7 mm thick) containing unavoidable impurities, it was subjected to annealing heat treatment at 780°C. During the above annealing heat treatment, the gas atmosphere inside the furnace is a reducing gas atmosphere with 4-20% H2 - The remaining N2 was controlled, and the dew point temperature was below -40°C.

[0048] Subsequently, the above test specimens were subjected to alloy hot-dip plating under the conditions shown in Table 1 below. At this time, it consisted of 22.77% Al, 3.6% Mg, and the remainder Zn by weight. An alloy plating bath with the specified composition (Fe 0.027%) was used.

[0049] [Table 1]

[0050] As described above, the appearance of the plating was observed for each plated steel sheet after the plating process was completed. The results are shown in Figure 1, and a photograph of the cross-section of the alloy plating layer observed by SEM is shown in Figure 2.

[0051] As shown in Figure 2, only test pieces 4 and 5, which correspond to Invention Examples 1 and 2, showed surface structure and internal structure. It can be confirmed that the weave is separated and formed uniformly. In particular, the alloy phase inside the plating layer It can be confirmed that they are formed uniformly.

[0052] In contrast, the test specimens of Comparative Examples 1 to 13 had Fe-Al alloy phases that were Zn phase and Zn-Al phase. It can be confirmed that it is formed by a mixture of these elements.

[0053] Furthermore, Figure 3 shows the microstructure of the alloy plating layers of Comparative Example 1 and Invention Example 2 as observed by SEM. This demonstrates the truth.

[0054] As shown in Figure 3, in Comparative Example 1, the plated steel sheet has the plating structure intended by the present invention. In contrast to the case where a uniform alloy plating layer having was not formed, in the second example of the invention, Fe-Al alloy A gold layer is formed inside the alloy plating layer, and a uniform plating structure is formed on the alloy layer. It can be confirmed that this has been done.

[0055] (Example 2) The same test specimen as in Example 1, i.e., a cold-rolled carbon steel test specimen (thickness 0.7 mm) After degreasing, the material was subjected to annealing heat treatment at 750°C. During the above annealing heat treatment, the gas atmosphere inside the furnace was The reducing gas atmosphere is controlled to be 4-20% H2-with the remainder being N2, and the dew point temperature is below -40°C. It was below.

[0056] Subsequently, alloy hot-dip plating was performed on the above test specimens under the conditions shown in Table 2 below. That's it.

[0057] [Table 2]

[0058] To evaluate the corrosion resistance of plated steel sheets after plating is completed under each condition, a salt spray test (KS) is performed. - After conducting an accelerated corrosion test using a salt spray standard test in accordance with C-0223, the plating layer The time elapsed until the area of ​​red rust on the surface reached 5% was measured.

[0059] Furthermore, to evaluate the plating adhesion, a 180-degree bending test was performed, and the bent surface was visually inspected. I sensed the problem and checked for cracks.

[0060] The results for each are shown in Table 3 below. As shown in Table 3 below, Invention Example A is superior to Comparative Example A. It exhibits excellent corrosion resistance, and it can be confirmed that no unplated areas are observed. In particular, Invention Example A The bending adhesion was at a level equivalent to that of hot-dip galvanized material.

[0061] [Table 3]

Claims

1. A base steel sheet and a Zn-Al-Mg alloy plating layer on at least one surface of the base steel sheet, A hot-dip galvanized steel sheet, The Zn-Al-Mg alloy plating layer has a weight percentage of aluminum (Al): 20-3 0%, magnesium (Mg): 3-5%, the remainder being Zn and other unavoidable impurities. The surface structure of the Zn-Al-Mg alloy plating layer consists of a Zn phase, a Zn-Al phase, and MgZn ２ Phase and Zn-Al-MgZn ２ It is composed of phases, and its internal structure includes an Fe-Al alloy phase. Hot-dip galvanized steel sheet with excellent corrosion resistance and workability.

2. The Zn-Al-Mg alloy plating layer is composed of aluminum (Al) and magnesium (Mg A molten metal containing 25% by weight or more of the total amount of the material described in claim 1, which has excellent corrosion resistance and processability. Steel plate.

3. The Zn-Al-Mg alloy plating layer has a thickness of 3 to 40 μm, as described in claim 1. Hot-dip galvanized steel sheet with excellent corrosion resistance and workability.

4. The surface structure of the Zn-Al-Mg alloy plating layer is defined as follows: From 1 / 3t to 1 / 2t in the direction (where t represents the thickness of the alloy plating layer (μm)) The region is the hot-dip galvanized steel sheet described in claim 1, which has excellent corrosion resistance and workability.

5. In weight percent, aluminum (Al): 20-30%, magnesium (Mg): 3-5% The steps include preparing an alloy plating bath containing the remaining Zn and other unavoidable impurities, The steps include: immersing a base steel sheet in the alloy plating bath and performing plating to manufacture a plated steel sheet; The steps include cooling the plated steel sheet at a cooling rate of 8 to 30°C / s, The aforementioned plating involves setting the plating bath intake temperature to 500-550°C and the plating bath temperature to 480-5 This process involves passing the material through a plating bath at a temperature of 50°C, resulting in a molten metal plating with excellent corrosion resistance and workability. A method for manufacturing steel plates.

6. The aforementioned cooling is performed at 300°C or below, and the molten metal with excellent corrosion resistance and processability as described in claim 5. A method for manufacturing steel plates.

7. The aforementioned cooling involves hydrogen (H) at a concentration of 4% by volume or less (including 0%). ２ ) and the remainder nitrogen (N ２ ) is composed of The hot-dip galvanized steel sheet described in claim 5, which is produced in a gas atmosphere, has excellent corrosion resistance and workability. Manufacturing method.

8. The step of gas wiping the plated steel sheet before the cooling step further includes A method for manufacturing a hot-dip galvanized steel sheet with excellent corrosion resistance and workability as described in claim 5.

9. The aforementioned base steel sheet is a cold-rolled material that has been degreased and annealed at a temperature range of 700 to 850°C. A method for manufacturing a hot-dip galvanized steel sheet with excellent corrosion resistance and workability as described in claim 5.

Images