Plated steel sheet with excellent corrosion resistance and weldability, and method for manufacturing the same.

Abstract

The present invention provides a plated steel sheet and a method for manufacturing the same, which are excellent in corrosion resistance and also in one or more properties among weldability and chemical conversion treatmentability. [Solution] A plated steel sheet comprising a base steel sheet and a Zn-Mg-Al plated layer provided on at least one surface of the base steel sheet, wherein the changes in Zn content and Al content in the surface layer region from the surface to a specific position in the thickness direction of the plated layer are controlled to satisfy a specific relational expression.

Description

[Technical Field]

[0001] This invention relates to a highly corrosion-resistant plated steel sheet with excellent corrosion resistance and weldability, and to a method for manufacturing the same. That is the case. [Background technology]

[0002] When zinc-plated steel sheets are exposed to a corrosive environment, zinc, which has a lower oxidation-reduction potential than iron, is the first to oxidize. It has the property of sacrificial corrosion protection, where it is corroded and the corrosion of the steel material is suppressed. In addition, the zinc in the plating layer is acid As the material oxidizes, a dense layer of corrosion products forms on its surface, shielding the steel from the oxidizing atmosphere. This improves the corrosion resistance of steel materials. Due to these advantageous properties, zinc-plated steel sheets are Recently, its application has expanded to include building materials, home appliances, and automotive steel sheets.

[0003] However, due to the increase in air pollution accompanying industrial advancement, the corrosive environment is gradually deteriorating, and resources Furthermore, due to stringent energy conservation regulations, it offers even better corrosion resistance than conventional galvanized steel. There is a growing need for the development of steel materials that possess [certain properties].

[0004] To improve this problem, aluminum (Al) and magnesium are added to the zinc plating bath. Manufacturing technology for zinc alloy plated steel sheets that improves the corrosion resistance of steel materials by adding elements such as (Mg). Various studies are underway on this topic. A typical example is the study on Zn-Al plating composition systems. There are also Zn-Mg-Al zinc alloy plated steel sheets with further added magnesium.

[0005] On the other hand, Zn-Mg-Al zinc alloy plated steel sheets are usually painted or welded before use. In many cases, however, if a large amount of Al is distributed on the surface of the plating layer, Al-based oxides may be present. There is a drawback in that the chemical conversion treatment property required for pre-painting treatment deteriorates, resulting in poor painting adhesion. Furthermore, due to the influence of Al vapor during arc welding, pores remain in the welded metal, causing a problem that the strength of the welded joint decreases.

[0006] In addition, galvanized steel sheets after processing are often provided on the outside of products, but due to deterioration of painting adhesion, surface damage factors such as partial peeling phenomena and poor shape of welded joints due to welding pores are added, resulting in insufficient surface quality and the need for improvement in appearance quality.

[0007] Therefore, technologies at a level that can meet all the above-described characteristics such as corrosion resistance, weldability, and chemical conversion treatment property have not been developed to meet the high-level demands with excellence.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] According to one aspect of the present invention, there is provided a plated steel sheet excellent in corrosion resistance and weldability and a method for manufacturing the same. To provide.

[0010] Furthermore, according to another aspect of the present invention, there is provided a plated steel sheet excellent in all of corrosion resistance, weldability, and chemical conversion treatment property and a method for manufacturing the same. To provide.

[0011] The problems of the present invention are not limited to the above-described content. Any person having ordinary knowledge in the technical field to which the present invention pertains can, from the entire content of the specification of the present invention, It is easy to understand. [Means for solving the problem]

[0012] One aspect of the present invention is, Raw steel sheet; and The above-mentioned base steel sheet includes a Zn-Mg-Al plating layer provided on at least one surface; The above-mentioned plating layer provides a plated steel sheet that satisfies the following relational equations 1 and 2. [Relationship 1] -10.0≦[Zn] 1 / 10t -[Zn] s ≤ -5.0 (In the above relational expression 1, the above [Zn] 1 / 10t It is 1 in the thickness direction from the surface of the plating layer / 10t represents the weight % content of Zn at the position (t is the total thickness of the plating layer), and the above [Z n] s (This represents the weight percentage content of Zn on the surface of the plating layer.) [Relationship 2] +3.0≦[Al] 1 / 10t -[Al] s ≤ +13.0 (In the above relational equation 2, the above [Al] 1 / 10t It is 1 in the thickness direction from the surface of the plating layer / 10t represents the weight % Al content at the position (t is the total thickness of the plating layer), and the above [A l] s (This represents the weight percentage content of Al on the surface of the plating layer.)

[0013] Another aspect of the present invention is, In a shot blast cabin where metal material circulates at a rotational speed of 1200-2000 mpm For the advancing steel plate, metal balls with a particle size of 0.6-1.0 mm are applied at 400-1200k This is the stage where primary shot blasting is performed, projecting the material onto the surface of the base steel plate at a rate of g / min. ; In a shot blast cabin where metal material circulates at a rotational speed of 1200-2000 mpm For the advancing steel plate, metal balls with a particle size of 0.2-0.5 mm are applied at 400-1200k This stage involves performing a secondary shot blasting treatment, projecting the projectiles onto the surface of the base steel plate at a rate of g / min. ; The above shot-blasted steel sheet contains, by weight %, Mg: 4.0-7.0%, Al : Contains 8.2-19.5%, with the remainder being Zn and other unavoidable impurities, solidifying on the equilibrium phase diagram. The device is immersed in a plating bath that maintains a temperature of Ts+20°C to Ts+80°C relative to the starting temperature (Ts). The stage of dipping and hot-dip galvanizing; The above hot-dip galvanized steel sheet is subjected to a process of heating from the solidification start temperature to the solidification end temperature at a rate of 2-8°C / s. A method for manufacturing plated steel sheets is provided, which includes a step of cooling with an inert gas at a uniform cooling rate. ru. [Effects of the Invention]

[0014] According to one aspect of the present invention, a plated steel sheet with excellent corrosion resistance and weldability, and a method for manufacturing the same, are provided. It can be provided.

[0015] Furthermore, according to another aspect of the present invention, excellent corrosion resistance, weldability, and chemical treatment properties are all present. We can provide a hardened steel plate and a method for manufacturing the same.

[0016] The diverse yet significant advantages and effects of this invention are not limited to those described above. This can be more easily understood in the process of describing specific embodiments of the invention. [Brief explanation of the drawing]

[0017] [Figure 1] This figure shows the component analysis profile using GDS for the plated steel sheet obtained from Example 7. [Modes for carrying out the invention]

[0018] The terms used herein are for illustrative purposes only and do not limit the invention. This is not the intention. Furthermore, the singular form used herein is as clearly defined in the relevant definitions. It includes multiple forms unless it expresses opposition to crabs.

[0019] In specifications, "includes" means to specify a configuration and exclude the existence or addition of other configurations. It's not something you should do.

[0020] Unless otherwise defined, this specification includes technical and scientific terms. All terms are as generally understood by a person with ordinary skill in the art to which this invention pertains. It has the same meaning as the meaning of "to be". Terms defined in dictionaries are related to the relevant technical documents and currently disclosed It is interpreted as having a meaning that corresponds to the content described.

[0021] The following describes in detail a "plated steel sheet" relating to one aspect of the present invention. When expressing the content of each element, unless otherwise specified, it refers to weight percent.

[0022] In conventional Zn-Mg-Al zinc alloy plated steel sheet related technologies, M is used to improve corrosion resistance. Although g was added, excessive Mg addition leads to increased generation of floating dross in the plating bath. There is a problem that dross must be removed frequently, so the upper limit of Mg addition is limited to 3%. there was.

[0023] Therefore, we conducted research to further improve corrosion resistance by increasing the amount of Mg added beyond 3%, The more magnesium (Mg) is added, the more significantly the amount of floating dross in the plating bath increases, making plating bath management difficult. In addition, the product's appearance darkens, and the addition of surface damage elements can compromise its appearance quality. There was a problem in that it was difficult to secure.

[0024] Therefore, in order to solve the above-mentioned problems, the amount of Al added increases as the amount of Mg added increases. By simultaneously raising them, Al oxide is preferentially formed on the plating bath surface over Mg oxide, A technology that suppresses floating dross in the g oxide substrate and prevents the product from easily blackening. An attempt had been made.

[0025] However, even if a component system with a high amount of Al is set, ensuring plating workability and appearance quality. However, the Al oxides that inevitably form on the surface of the plating layer cause deterioration of paint adhesion. This includes surface damage factors such as partial delamination and deformation of welded joints due to welding pores. This presented a problem in ensuring the quality of the appearance after painting and welding. .

[0026] Therefore, conventional technology ensures excellent corrosion resistance while simultaneously providing excellent weldability and / or chemical treatment properties. Providing Zn-Mg-Al zinc alloy plated steel sheets that even ensure rationality is technically challenging. It was difficult.

[0027] Therefore, the present inventors have solved the above-mentioned problems while simultaneously providing not only corrosion resistance but also weldability In order to provide plated steel sheets that are also excellent in chemical treatment properties, we have conducted thorough research and found that After removing the effects of oxidation from the plated layer, at a position 1 / 10th of the thickness direction from the surface of the plated layer ( (where t is the total thickness of the plating layer) Each component in the surface region up to that point (e.g., Zn and Al, ) Furthermore, we discovered that changes in the content of (including Mg) are an important factor, and thus completed the present invention. It came to this point.

[0028] Therefore, the following properties are excellent in corrosion resistance, as well as weldability and / or chemical treatment properties. This section will specifically explain the composition of plated steel sheets, which also have excellent properties.

[0029] First, the plated steel sheet according to the present invention is a base steel sheet; at least one surface of the base steel sheet is provided It contains a Zn-Mg-Al plated layer.

[0030] In the present invention, the type of base steel sheet is not particularly limited. For example, the above base The base steel sheet is an Fe-based base steel sheet, which is used as the base steel sheet for ordinary zinc-plated steel sheets. It may be, but is not limited to, hot-rolled steel sheet or cold-rolled steel sheet. Alternatively, the above Raw steel sheets include carbon steel and ultra-low carbon steel, which are used as materials for construction, home appliances, and automobiles, for example. It can also be steel or high-manganese steel.

[0031] However, as an example, the above-mentioned base steel sheet has a C content exceeding 0% by weight (more preferably 0%). (0.001% or more) 0.18% or less, Si: greater than 0% (more preferably 0.001% or more) 1.5% or less, Mn: 0.01 to 2.7%, P: greater than 0% (more preferably 0.001%) % or more) 0.07% or less, S: exceeding 0% (more preferably 0.001% or more) 0.01 5% or less, Al: greater than 0% (more preferably 0.001% or more), 0.5% or less, Nb: More than 0% (more preferably 0.001% or more) 0.06% or less, Cr: more than 0% ( Preferably, 0.001% or more, 1.1% or less, Ti: greater than 0% (more preferably 0. (0.001% or more) 0.06% or less, B: greater than 0% (more preferably 0.001% or more) It can have a composition containing 0.03% or less, with the remainder being Fe and other unavoidable impurities. .

[0032] Although not particularly limited, according to one embodiment of the present invention, at least the above-mentioned base steel sheet On one side, a Zn-Mg-Al plating layer made of a Zn-Mg-Al alloy is provided. This is possible. The above plating layer may be formed on only one surface of the base steel sheet, or This can also be formed on both sides of the base steel sheet. In this case, the above Zn-Mg-Al system The plating layer contains Mg and Al, and mainly Zn (i.e., 50% or more Zn). This refers to the plating layer.

[0033] Although not particularly limited, according to one embodiment of the present invention, the Zn-Mg-Al system The thickness of the plating layer can be 9 to 100 μm, more preferably 20 to 90 μm. This is possible. If the thickness of the plating layer is less than 9 μm, it will result from the thickness deviation of the plating layer. Due to errors, the plating layer may be too thin in some areas, resulting in poor corrosion resistance. If the thickness exceeds 100 μm, the cooling of the molten plating layer may be delayed, for example. There is a possibility of solidification defects occurring on the surface of the plating layer, such as a dripping shape, and to solidify the plating layer... This can lead to a decrease in the productivity of steel plate production.

[0034] On the other hand, although not particularly limited, according to one embodiment of the present invention, the above-mentioned base steel sheet and A Fe-Al-based suppression layer can be further included between the Zn-Mg-Al-based plating layer and the Zn-Mg-Al-based plating layer. The above Fe-Al-based suppression layer mainly contains intermetallic compounds of Fe and Al (for example, 60% or less). The upper layer consists of intermetallic compounds of Fe and Al, such as FeAl, FeAl3, and Fe2Al5. These are some examples. In addition, some components originating from the plating layer, such as Zn and Mg, For example, it may contain even less than 40%. The above suppression layer is from the initial plated steel sheet. This layer is formed by alloying with diffused Fe and plating bath components. The above-mentioned suppression layer is It plays a role in improving the adhesion between the base steel sheet and the plating layer, and at the same time, it helps to improve the adhesion between the base steel sheet and the plating layer It can serve to prevent Fe diffusion into the substrate. The above-mentioned suppression layer is made of Zn-M It can be formed continuously with the g-Al plating layer, or discontinuously. It is also possible. In this case, with respect to the above-mentioned suppression layer, except for the explanation above, in the relevant technical field The commonly known information can be applied in the same way.

[0035] Although not particularly limited, according to one embodiment of the present invention, the thickness of the suppression layer is 0. The thickness can be 0.1 to 2.50 μm. The above suppression layer prevents alloying and ensures corrosion resistance. It plays a role in this, but because it is a brittle, it can affect processability, and its thickness It can be reduced to 2.50 μm or less. However, in order to function as an inhibitory layer, The thickness can be increased to 0.01 μm or more. From the perspective of further improving the effects mentioned above. Preferably, the upper limit of the thickness of the suppression layer can be 1.80 μm. The lower limit of the thickness of the suppression layer can be 0.02 μm. In this case, the thickness of the suppression layer is This can mean the minimum thickness in the direction perpendicular to the interface of the base steel sheet.

[0036] On the other hand, although not particularly limited, according to one embodiment of the present invention, the above Zn-Mg- The Al-based plating layer consists of Mg: 4.0-7.0% by weight, Al: 8.2-19.5%, and the remainder... It may contain Zn and other unavoidable impurities. The following describes each component in detail. I will explain it to them.

[0037] Mg: 4.0% or more and 7.0% or less Mg is an element that plays a role in improving the corrosion resistance of plated steel materials, and in this invention, the objective is To ensure excellent corrosion resistance, the Mg content in the plating layer is controlled to 4.0% or higher. On the other hand, if too much magnesium is added, dross may occur, therefore, the magnesium content Control it to 7.0% or less. On the other hand, from the viewpoint of maximizing the above-mentioned effect, it is more preferable. The lower limit of the above Mg content can be 4.7%, or the upper limit of the above Mg content It can be 6.0%.

[0038] Al: 8.2% or more and 19.5% or less Generally, when Mg is added at a concentration of 1% or more, the effect of improving corrosion resistance is observed, but when Mg is 2% Adding more than % increases the generation of floating dross in the plating bath due to the oxidation of Mg in the plating bath. There is a problem that dross needs to be removed frequently. Due to this problem, conventional technology Therefore, to ensure corrosion resistance, Zn-Mg-Al zinc alloy plating is used with the addition of 1.0% or more of Mg. However, the upper limit for Mg content was set at 3.0% for regular use. However, as mentioned above... To further improve corrosion resistance, the Mg content needs to be increased to 4% or more, but If the plating layer contains more than 4% Mg, a problem arises where dross is generated due to the oxidation of Mg in the plating bath. Therefore, it is necessary to add 8.2% or more of Al. However, Al is used to suppress dross. Adding too much of it raises the melting point of the plating bath, which in turn causes the operating temperature to become too high. Therefore, problems arise due to high-temperature work, such as erosion of the plating bath structure and deformation of the steel material. Furthermore, if the Al content in the plating bath is excessive, the Al will react with the Fe in the base iron. Consequently, it does not contribute to the formation of the Fe-Al inhibitory layer, and the reaction between Al and Zn occurs rapidly, resulting in the formation of a large aggregate. The over-formation of the outburst phase may deteriorate the corrosion resistance instead. Therefore, it is preferable to control the upper limit of the Al content in the plating layer to 19.5%. On the other hand, from the viewpoint of maximizing the above-described effects, more preferably, the lower limit of the Al content can be 11.0%, or the upper limit of the Al content can be 18.0%.

[0039] The balance is Zn and other inevitable impurities Except for the composition of the above-described plating layer, the balance can be Zn and other inevitable impurities. Inevitable impurities can all be included as long as they are unintentionally mixed in the manufacturing process of ordinary hot-dip galvanized steel sheets. Those skilled in the art can easily understand the meaning.

[0040] According to the present invention, the above plating layer satisfies the following relational expressions 1 and 2. [Relational expression 1] -10.0 ≤ [Zn] 1 / 10t - [Zn] s ≤ -5.0 (In the above relational expression 1, the above [Zn] 1 / 10t represents the weight% content of Zn at the 1 / 10t position (t is the total thickness of the plating layer) in the thickness direction from the surface of the plating layer, and the above [Z n] represents the weight% content of Zn on the surface of the plating layer.) s [Relational expression 2] +3.0 ≤ [Al] 1 / 10t - [Al] s ≤ +13.0 (In the above relational expression 2, the above [Al] 1 / 10t represents the weight% content of Al at the 1 / 10t position (t is the total thickness of the plating layer) in the thickness direction from the surface of the plating layer, and the above [A l] represents the weight% content of Al on the surface of the plating layer.) s ​​(This represents the weight percentage content of Al on the surface of the plating layer.)

[0041] The inventors have ensured improved corrosion resistance compared to the prior art, while simultaneously providing weldability and / or After diligent research to ensure chemical conversion treatment suitability, we found that the effects of oxidation in the plating layer were... Excluding the area from the surface of the plating layer to the 1 / 10t position in the thickness direction (where t is the total thickness of the plating layer) Changes in the content of each component (e.g., Zn and Al, and also Mg) in the surface region. We found that transformation is a crucial element.

[0042] In the present invention, the above Zn-Mg-Al plating layer is common in high corrosion-resistant plated steel sheets. The resulting phases can include a single Zn phase and a Zn-MgZn2-Al ternary eutectic phase. Generally, the lower the Al and Mg content in the plating layer, the more the above-mentioned Zn single phase and The amount of Zn-MgZn2-Al ternary eutectic phase generated increases, and Al and in the plating layer The higher the Mg content, the greater the amount of MgZn2 phase and Al single phase that tends to be produced. In this case, in a plating component system like the present invention, where the Mg content is 4% or more, the Mg content As the quantity increases, the Al content must also increase simultaneously to suppress dross, Accordingly, the Al single phase also comes to coexist. Therefore, the inventors continued their research and Furthermore, the nucleation and growth of the MgZn2 phase and Al single phase described above are suppressed on the surface of the plating layer, Promoting this process within the layer results in the formation of a single-phase Zn and an Al-Zn binary eutectic phase on the surface of the plating layer. The distribution of the Zn-MgZn2-Al ternary eutectic phase can be increased, and the Zn component content can be increased. It was found that this contributes to the creation of a plated layer surface with a high Al content while simultaneously having a low Al content. I took it out.

[0043] In other words, the inventors have achieved, at the same time as ensuring the corrosion resistance described above, directly improving weldability and chemical treatment properties. The area affected by contact is the surface layer of the plating layer, from the surface to the 1 / 10th position in the thickness direction. It was confirmed that this was the region. Therefore, the Zn content in the surface region of the above plating layer. By controlling the changes in and the Al content so that the above-mentioned relational equations 1 and 2 are satisfied, It is possible to effectively obtain plated steel sheets that have excellent corrosion resistance as well as weldability and / or chemical treatment properties. It was discovered that...

[0044] On the other hand, although not particularly limited, according to one embodiment of the present invention, the above-mentioned effects can be achieved From the viewpoint of maximizing, more preferably [Zn] defined by the above relational expression 1 1 / 10t - [Zn] s The lower limit of the value can be -9.9, or the above [Zn] 1 / 10t -[ Zn] s The upper limit of the value can be -5.3 (most preferably -7.0). Also, [Al] defined in relation 2 1 / 10t -[Al] s The lower limit of the value is +6.4. This is possible, or the above [Al] 1 / 10t -[Al] s The upper limit of the value is +11.1. It is possible.

[0045] Furthermore, although not particularly limited, according to one embodiment of the present invention, the inventors have found that As a result of diligent research to further improve the dietary properties, selectively satisfying the following relational equation 3. By controlling the Mg content profile in the thickness direction, uniform corrosion can be achieved in the thickness direction. As the erosion progresses, it has the effect of improving to an even higher level of corrosion resistance. They discovered it. [Relationship 3] -1.0 ≤ [Mg] 1 / 10t -[Mg] s ≤ +1.0 (In the above relational equation 3, the above [Mg] 1 / 10t It is 1 in the thickness direction from the surface of the plating layer / 10t represents the weight % content of Mg at the position (t is the total thickness of the plating layer), and the above [M g] s (This represents the weight percentage content of Mg on the surface of the plating layer.)

[0046] According to one embodiment of the present invention, the corrosion resistance mechanism of the Zn-Mg-Al plated layer is made The sacrificial corrosion protection cell used has a potential of MgZn2 at -1.2V above the hydrogen reduction potential, and the Al is By ensuring a large potential difference with the position set to -0.7V above the hydrogen reduction potential, the anode and cathode are respectively connected. Acting as an electrode, it galvanizes the microstructure between the adjacent MgZn2 phase and Al single phase. It forms galvanic cells. In other words, as corrosion progresses, dissolves The anode (MgZn2) of the sacrificial corrosion protection cell where the plating is performed is irregularly formed in the depth direction of the plating layer. If present, the anode of the galvanic cell having the excellent corrosion resistance and sacrificial corrosion protection described above. - The cathode potential difference is formed to differ depending on the position of the plate, causing corrosion to occur first in specific areas. Therefore, corrosion can proceed unevenly depending on the location. Thus, the above relational equation 3 is satisfied. By controlling the change in Mg content in the surface layer of the plating layer to minimize it, uniformity in the thickness direction can be achieved. This can accelerate corrosion and further improve overall corrosion resistance.

[0047] On the other hand, although not particularly limited, according to one embodiment of the present invention, the above-mentioned effects can be achieved From the viewpoint of maximizing, more preferably [Mg] as defined in relational equation 3 above. 1 / 10t - [Mg] sThe lower limit of the value can be -0.8, or the above [Mg] 1 / 10t -[ Mg] s The upper limit of the value can be +0.8.

[0048] The content of each component at the 1 / 10t position and the plating layer as defined by the relational equations 1 to 3 described above. The method for measuring the content of each component on the surface is not particularly limited, but for example, It can be measured using methods such as the following.

[0049] In other words, after cutting the plated steel material vertically, a glow discharge spectrometer (GDS; Gl ow Discharge Optical Emission Spectromet Using ry), the content of each component such as Zn, Al, Mg, and Fe in the cross-section of the plating layer The distribution of the amount is measured. Subsequently, in order to eliminate the influence of oxidation of the plating layer, the present invention The region from the outermost surface of the plating layer to a thickness of 0.1 μm is excluded. Therefore, this specification In this context, the "surface of the plating layer" refers to the region excluding the area affected by the oxidation described above. This refers to a point 0.1 μm from the outermost surface of the plating layer in the thickness direction. Therefore, the upper The content of each component on the surface of the plating layer, as defined by equations 1 to 3, is the content of each component on the outermost surface of the plating layer. This is defined as the content of each component (Zn, Al, and Mg) at a position 0.1 μm from the surface. can.

[0050] On the other hand, the content of each component at a position 1 / 10t in the thickness direction from the surface of the aforementioned plating layer To define this, the overall plating layer thickness (t) is determined by the individual components measured using the above GDS. Based on the profile, the Zn and Fe content from the surface of the plating layer matches each other. The distance to the position is defined as t. This means that 1 / 1 of the total thickness t of the plating layer is obtained. Since the 0t position can be defined, each component measured by GDS at the point where it becomes 1 / 10t ( The content of Zn, Al, and Mg can be measured.

[0051] For example, in the case of Example 7 defined in Figure 1, the Zn and Fe content are equal. The value of t to the position is approximately 34 μm. Therefore, the 1 / 10t position is on the surface of the plating layer. This means a point approximately 3.4 μm from the surface of the plating layer. By measuring the weight percentage content of each component at a given point, [Zn] 1 / 10t [Al] 1 / 10t [Mg] 1 / 10t The value can be measured.

[0052] Furthermore, although not particularly limited, according to one embodiment of the present invention, the surface of the plating layer The weight percentage of Mg at the 2 / 3t position in the thickness direction from the surface is the weight of Mg in the plating layer. The content can be within a range of ±0.5 wt% relative to the average % content. This allows corrosion to progress uniformly in the thickness direction, resulting in an even higher level of corrosion resistance. They can wield power.

[0053] On the other hand, although not particularly limited, from the perspective of maximizing the effects mentioned above, Alternatively, the weight percentage content of Mg at a position 2 / 3t in the thickness direction from the surface of the above-mentioned plating layer is The average weight percentage content of Mg in the plating layer can be kept within a range of ±0.3 wt%. ru.

[0054] In this case, the method for measuring the weight-percentage average content of Mg in the plating layer is not particularly limited. It is not possible. However, as an example, the Mg content in the thickness direction measured using the GDS described above. Based on the change in quantity, excluding the region from the outermost surface of the plating layer to 0.1 μm, the shortest distance t After measuring the Mg content at each point every 0.5 μm, the average value calculated from this was... It can be defined as follows.

[0055] Furthermore, the weight percentage of Mg at a position 2 / 3t in the thickness direction from the surface of the above-mentioned plating layer is Similarly, excluding the region from the outermost surface of the plating layer to 0.1 μm, the previously defined t is used as a basis. This can be interpreted as the Mg content at the 2 / 3t position.

[0056] On the other hand, although not particularly limited, according to one embodiment of the present invention, selectively, the above The area fraction of the Al single phase with a Zn solid solution ratio of 27 atomic% or more on the surface of the layer is 2.0 to 10. It can be 1%. The area fraction of the Al single phase with a Zn solid solution ratio of 27 atomic% or more is 2.0 If the percentage is less than 10.0%, one or more of the following properties will be affected: weldability and chemical conversion treatmentability. There is room for this to worsen. From the viewpoint of further improving the above-mentioned effect, preferably the above Z The lower limit of the area fraction of Al single phase with a solid solubility of n of 27 atomic percent or more can be 2.2%, The upper limit of the area fraction of the Al single phase with a Zn solid solution ratio of 27 atomic% or more is 4.0%. It is possible.

[0057] In this specification, Al single phase refers to a phase mainly composed of Al, regardless of the Zn solid solution ratio. This refers to the phase in which solid-solution Zn and impurities such as Mg that are inevitably present are removed. This refers to a phase where the remainder is Al. Specifically, in conventional technology, Al is typically used as a single phase. It was known that only a single Al phase with a low Zn solid solution ratio of less than 27% existed. However, this After diligent investigation, the inventors concluded that the Al single phase present on the surface of the plating layer has a Zn solid solubility of 2 In addition to Al single-phase with a low Zn solid solution content of less than 7%, there are also Al single-phase with a high Zn solid solution content of 27% or more. It was found that... Furthermore, the aforementioned corrosion resistance, weldability, and chemical treatment properties were further improved... To achieve this, the area ratio of the Al single phase with a Zn solid solution ratio of 27% or more is controlled to be low, but 2.0 area A higher percentage of the plated layer is formed on the surface of the plating layer, which negatively affects weldability and chemical conversion treatment properties. It was found to be an effective element from the perspective of reducing Al oxides.

[0058] Furthermore, the area of ​​the Al single phase on the surface of the above-mentioned plating layer in which the Zn solid solution ratio is 27 atomic percent or more The method for measuring the rate is not particularly limited. However, as an example, scanning electron microscope (SEM) The image derived under the measurement conditions of ) was processed by RISA (microscopic) at Pohang Institute of Science and Industry (RIST). Super-pixel algorithm (a software for analyzing tissue phase fractions) The system utilizes a base and image automatic generation software. The superpixel algorithm is the overall image The image is divided into thousands to tens of thousands of regions (superpixels), and similar patterns and features are identified. The superpixels were compared to measure similarity, and the histogram was used to determine the brightness value of the pixels. After calculating the RUM, if the similarity is above a predefined threshold, superpixels are automatically generated. This is a mechanism for selecting. As an example of specifying a predefined threshold, derived from SEM The boundary of the Al single-phase in the image above is solid-dissolved Zn within the Al single-phase structure using EDS. By pre-defining each phase based on a solid solubility of 27 atomic percent, the brightness value in the software can be determined. This enables histogram creation and tissue differentiation. The technical ideas behind the analysis software are described in Korean Public Bulletin No. 2019-0078331. It can be confirmed by checking.

[0059] Next, a "method for manufacturing plated steel sheets" relating to another aspect of the present invention will be described in detail. However, the plated steel sheet of the present invention does not necessarily have to be manufactured by the following manufacturing method. That is not what it means.

[0060] According to one embodiment of the present invention, the process may further include the step of first preparing a base steel sheet. The type of base steel sheet is not particularly limited. This can be an Fe-based steel sheet, that is, a hot-rolled steel sheet or a cold-rolled steel sheet, but It is not limited to these uses. Furthermore, the above-mentioned raw steel sheets are, for example, used in construction, home appliances, and automobiles. The material used can be carbon steel, very low carbon steel, or high manganese steel, however It is not limited to this. In this case, the above explanation applies to the raw steel sheet as described above. It can be applied.

[0061] According to the present invention, a shot blob in which metal material is circulated at a rotational speed of 1200 to 2000 mpm Four metal balls with a particle size of 0.6 to 1.0 mm are applied to the steel plate moving through the last cabin. Primary shot blasting is performed on the surface of the raw steel plate at a rate of 00-1,200 kg / min. The process is carried out. By fulfilling the conditions for the above primary shot blasting treatment, the substrate before plating is processed. This method primarily removes surface oxides from steel plates, thereby minimizing the effects of oxides. It is possible.

[0062] Following the above primary shot blasting process, the metal is subjected to a rotational speed of 1200-2000 mpm. For steel plates being blasted in a shot blasting cabin where the material is circulated, the particle size is 0.2 to 0.5 A metal ball measuring 400-1200 kg / min is projected onto the surface of the bare steel plate. A secondary shot blasting treatment is performed. The conditions for the above secondary shot blasting treatment are met. This imparts fine plastic deformation to the surface of the steel plate, causing dislocations in the underlying iron structure. This ensures the effect of increasing density and activating the plating reaction.

[0063] Next, the base steel sheet that has undergone the above primary and secondary shot blasting treatment is subjected to a treatment in which Mg: 4.0-7.0%, Al: 8.2-19.5%, the remainder being Zn and other unavoidable impurities. Furthermore, the temperature range is Ts+20°C to Ts+80°C relative to the solidification initiation temperature (Ts) on the equilibrium phase diagram. The immersion is immersed in a maintained plating bath to perform hot-dip zinc plating.

[0064] In this case, according to one embodiment of the present invention, the reason for adding components to the plating bath as described above and The reason for limiting the content is to allow for the inclusion of a small amount of Fe that may flow in from the base steel sheet. Except for the above, the same explanation for the components of the plating layer can be applied.

[0065] On the other hand, in order to produce a plating bath with the above composition, a predetermined amount of Zn, Al, and Mg is required. Using composite ingots or Zn-Mg and Zn-Al ingots containing individual components This is possible. In order to replenish the plating bath consumed in molten plating, the above ingot can be used. Furthermore, it will be supplied after being dissolved. In this case, the ingot is directly immersed in the plating bath and dissolved. You can also choose a method where the ingot is melted in a separate port, and then the molten metal is... You can also choose a method to replenish the plating bath.

[0066] Furthermore, the temperature of the plating bath is 20 to 80°C relative to the solidification initiation temperature (Ts) on the equilibrium phase diagram. It can be maintained at high temperatures (i.e., Ts+20℃ to Ts+80℃). While not particularly limited, the solidification initiation temperature on the above equilibrium phase diagram is 390-460°C. The temperature can be within this range, or the temperature of the plating bath can be maintained in the range of 440-520°C. This can be done. The higher the temperature of the plating bath, the better the fluidity and uniformity within the plating bath can be ensured. This allows for the formation of a suitable composition and reduces the amount of suspended dross generated. If the temperature is below Ts+20℃, the ingot dissolves very slowly, and the viscosity of the plating bath is high. It can be difficult to ensure excellent surface quality of the plating layer if the temperature of the plating bath is Ts When the temperature exceeds +80°C, ash defects due to Zn evaporation are induced on the plated surface. There is a possibility that problems may arise.

[0067] On the other hand, the above hot-dip galvanized steel sheet is measured from the solidification start temperature to the solidification end temperature, based on the surface temperature. The temperature is cooled using an inert gas at an average cooling rate of 2 to 8°C / s. According to the present invention, This slow cooling process promotes nucleation and growth into the interior of the plating layer rather than on the surface of the plating layer. This can contribute to the above. Therefore, the average cooling rate is less than 2°C / s. Then, the MgZn2 structure develops very coarsely on the surface, and the entire plating layer becomes brittle. As the material becomes tl, crack formation becomes more severe, making it difficult to ensure uniform corrosion resistance and workability. This is possible. On the other hand, if the average cooling rate exceeds 8°C / s, the liquid in the molten plating process The change from phase to solid phase occurs excessively rapidly, resulting in the formation of a locally non-uniform phase on the surface of the plating layer. This can result in color deviation in the width direction of the plated steel sheet and a decrease in corrosion resistance.

[0068] Furthermore, although not particularly limited, according to one embodiment of the present invention, the above solvent can be selectively used. Before hot-dip galvanizing, the shot-blasted base steel sheet is subjected to a surface roughness Ra of 1. Using dull rolls with a thickness of 0.8 to 2.8 μm, roll reduction of 100 to 400 tons is applied to the steel plate surface. This step may further include a pre-temper rolling step.

[0069] The inventors of this invention are diligently conducting research to further improve weldability and / or chemical treatment properties. As a result, using a dull roll that satisfies the above conditions, pre-conditioning pressure By performing a sprucing (SPM) treatment, the surface shape of the base steel sheet can be controlled to be irregular. This allows the subsequent plating process to maximize the number of solidification nuclei generated within the plating layer. It was found that it exhibits a transformative effect.

[0070] Specifically, if the surface roughness Ra of the above-mentioned dull roll is less than 1.8 μm, then within the plating layer A problem can arise where nucleation in the surface layer of the plating layer is promoted more than nucleation in the surrounding area. On the other hand, if the surface roughness Ra of the above-mentioned dull roll exceeds 2.8 μm, excessive indentations will form on the base steel sheet. Scratches occur, and the thickness of the molten plating layer formed by the subsequent plating process becomes uneven in the width direction. Sometimes problems arise where the result is one.

[0071] Furthermore, the roll reduction of the above-mentioned dull roll is less than 100 tons. Therefore, the shape control effect of the base steel sheet is low, and the effect of promoting solidification nucleation inside the plating layer as described above is low. It is difficult to wait, and the roll pressure of the above dull roll is 400 If the amount exceeds ton, it may induce warping of the base steel sheet, etc., in the direction of the plating layer thickness. It is difficult to expect a uniform contribution to formation.

[0072] As mentioned above, by precisely controlling the plating composition and manufacturing conditions, not only corrosion resistance but also Furthermore, it is possible to effectively provide plated steel sheets that are excellent in both weldability and / or chemical treatment properties. Cut. [Examples]

[0073] The present invention will be described more specifically below through examples. However, the following examples are illustrative. This is for the purpose of explaining the present invention and is not intended to limit the scope of the rights of the present invention. It is necessary to note that the scope of the present invention is limited to the matters described in the claims and the following: This is because it is determined by factors that can be reasonably inferred from it.

[0074] (Examples) C:0.018%, Si:0.01%, Mn:0.2%, P:0.009%, S:0. 005%, Al: 0.1%, Nb: 0.02%, Cr: 0.2%, Ti: 0.02%, B A base steel sheet having a composition of 0.015% and the remainder being Fe and impurities, as described in Table 1 below. Primary and secondary shot blasting were performed under the specified conditions. Subsequently, the conditions listed in Table 1 below were met. To achieve this, pre-temper rolling (SPM) treatment was performed. After this, the plating baths listed in Table 2 below were used. After performing hot-dip galvanizing to satisfy the composition (remaining Zn and impurities) and plating bath temperature, The system was cooled using inert gas N2 to satisfy the conditions shown in Table 2 below.

[0075] [Table 1] Bright*: Uses bright rolls with a surface roughness Ra of 0.2-0.6 μm. Dull*: Uses dull rolls with a surface roughness Ra of 1.8-2.8 μm.

[0076] [Table 2] Ts*: Solidification onset temperature on the equilibrium phase diagram [°C] Te*: Solidification completion temperature [°C]

[0077] After preparing the aforementioned plated steel sheet test specimens and dissolving the plating layer in hydrochloric acid solution, the dissolved material was then... The composition of the plating layer was measured by analyzing the liquid using the wet chemistry (ICP) method, and is shown in Table 3 below. (However, the remainder consists of Zn and impurities.)

[0078] Furthermore, the interface between the plating layer and the base iron can be observed in the thickness direction of the steel sheet (i.e., the pressure After preparing cross-sectional test specimens cut in a direction perpendicular to the extension direction, a scanning electron microscope (SEM) is used to analyze them. The image shows a 0.02 μm thick Fe-A layer between the base steel sheet and the Zn-Mg-Al plating layer. We confirmed that an I-system inhibitory layer was formed.

[0079] Furthermore, a GDS measuring device was used to analyze the components of the plated layer from the surface in the thickness direction, including Zn. The content of each component, Al, and Mg at the 1 / 10t position and the effect of oxidation. To remove it, we exclude the region up to a point 0.1 μm from the surface, and at the above 0.1 μm point... The content was measured on a certain surface and is shown in Table 3 below.

[0080] [Table 3] [Zn] 1 / 10t : From the surface of the plating layer, at a position 1 / 10t in the thickness direction (t is the thickness of the plating layer) Zn content by weight (in total thickness) [Zn] s : Weight % content of Zn on the surface of the plating layer [Al] 1 / 10t : From the surface of the plating layer, at a position 1 / 10t in the thickness direction (t is the thickness of the plating layer) Al content (by weight %) in total thickness [Al] s : Weight % content of Al on the surface of the plating layer [Mg] 1 / 10t : From the surface of the plating layer, at a position 1 / 10t in the thickness direction (t is the thickness of the plating layer) Mg weight % content (overall thickness) [Mg] s : Mg weight % content on the surface of the plating layer

[0081] Furthermore, the weight percentage content of Mg at a position 2 / 3t in the thickness direction from the surface of the plating layer is specified. The measurement was performed in the same manner as described above in the detailed document. Similarly, the weight % average content of Mg in the plating layer was also measured. The measurements were taken in the same manner as described above in the specification.

[0082] Furthermore, after imaging the surface of the plating layer with SEM, the Al single phase with a Zn solid solution content of 27 atomic% or more was detected. The area ratio was measured. The above values ​​are shown in Table 4 below.

[0083] [Table 4] S Al *: Area percentage of Al single phase with a Zn solid solution ratio of 27 atomic% or more on the surface of the plating layer. [%]

[0084] The characteristics of each example and comparative example were evaluated according to the following criteria, and the evaluation results of the characteristics are shown in Table 5 below. As shown.

[0085] <Corrosion resistance> To evaluate corrosion resistance, a salt spray tester is used. The following criteria were used to evaluate the product using a test method compliant with ISO 14993. ◎: The time required for red rust formation is 40 times longer than for Zn plating of the same thickness. ○: The time required for red rust to form is 30 to 40 times longer than that of Zn plating of the same thickness. △: The time required for red rust to form is 20 to less than 30 times longer than that required for Zn plating of the same thickness. ×: The time required for red rust formation is less than 20 times longer than for Zn plating of the same thickness.

[0086] <Chemical treatment properties> To evaluate the chemical treatment properties, the steel sheet was subjected to the following steps in order: degreasing, washing, surface preparation, and phosphate treatment. The experiment was conducted, and the free acidity in the phosphate solution was 0.7-0.9. The acidity (Total Acid) is 19-21, and the accelerator level is The value was set to 4-4.5. In addition, a scanning electron microscope (SEM) was used to examine any three surfaces of the steel plate. The point is magnified 1,000 times for observation, and the length of the phosphate particles is observed within a single field of view. After selecting 20 items in descending order of size, calculate the average, then find the average of the three locations again, The following evaluations were made based on the value of [the variable]. ○: Longitudinal length of phosphate particles < 5 μm △: Longitudinal length of phosphate particles: 5-8 μm ×: Longitudinal length of phosphate particles > 8 μm

[0087] <Weldability> To evaluate weldability, we assess the amount of spatter generated and the tensile strength of the weld, which affect weldability. Porosity, which affects strength, was evaluated. The above weldability evaluation was performed using gas CO2 and welding material KC- 28 solid wire, current 150A, voltage 20V, welding speed 0.6m / min Gas metal arc (GMA) welding was performed under the specified conditions. The amount of spatter generated was measured in the first 5 seconds after the start of welding. Five photographs were taken at each position to compare the relative occurrences, and the weld porosity was determined after non-destructive radiation testing of the weld. The distribution rate (%) of porosity defects relative to the weld line was measured. ○: Sputtering amount less than 5 times and porosity less than 15% compared to Zn plating of the same thickness. △: Sputtering amount 5 to less than 15 times that of Zn plating of the same thickness, porosity 15% or more. Less than 30% ×: Sputtering amount 15 times or more, porosity 30% or more compared to Zn plating of the same thickness.

[0088] Furthermore, the corrosion resistance, chemical treatment properties, and weldability of the steel plates obtained from each example and comparative example are examined. Sexuality was evaluated, and the evaluation results are shown in Table 5 below.

[0089] [Table 5]

[0090] As can be seen from Table 5 above, Example 1 satisfies all of the plating composition and manufacturing conditions of the present invention. In case 9, by satisfying relational formulas 1 and 2 as defined in the present invention, the corrosion resistance of the plated steel sheet is We confirmed that at least one of the properties of chemical conversion treatmentability and weldability was superior to that of the comparative example. Ta.

[0091] In particular, in the cases of Examples 7 to 9 above, Mg is present from the surface of the plating layer to the 2 / 3t position in the thickness direction. The weight percentage content satisfies ±0.5 wt% of the average weight percentage content of Mg in the plating layer. As a result, it exhibited even better corrosion resistance than Examples 1-6.

[0092] On the other hand, in the case of Comparative Examples 1 to 4, which do not satisfy the plating composition of the present invention, the above-mentioned corrosion resistance and chemical treatment We confirmed that one or more properties among rationality and weldability deteriorated.

[0093] Specifically, in Comparative Examples 1 and 3, the Mg content of the plating layer was insufficient, resulting in the lowest corrosion resistance. Not only does it deteriorate, but [Al] defined from relation 2 1 / 10t -[Al] s The value It was confirmed that the chemical treatment properties and weldability deteriorated when the material was not sufficient.

[0094] Furthermore, in Comparative Examples 2 and 4, the Mg content of the plating layer is satisfied, and corrosion resistance can be ensured. However, since the relational equations 1 and 2 are not satisfied, and the Al content on the surface of the plating layer is excessive, chemical treatment The rationality and weldability have deteriorated significantly.

[0095] Furthermore, Comparative Examples 5 to 8 satisfy the plating composition specified in the present invention but do not satisfy the manufacturing conditions. In this case, even if corrosion resistance can be ensured by satisfying the plating composition, if relational equations 1 and 2 are not satisfied The absence of this material resulted in a deterioration of chemical treatment properties and weldability.

Claims

1. Raw steel sheet; and A Zn-Mg-Al plating layer is provided on at least one surface of the base steel sheet; The aforementioned plating layer is a plated steel sheet that satisfies the following relational equations 1 and 2. [Relationship 1] -10.0≦[Zn] １／１０ｔ -[Zn] ｓ ≦-5.0 (In relational expression 1 above, the [Zn] １／１０ｔ It is 1 in the thickness direction from the surface of the plating layer / This represents the weight % content of Zn at the 10t position (where t is the total thickness of the plating layer), and the above [Z n] ｓ (This represents the weight percentage content of Zn on the surface of the plating layer.) [Relationship Equation 2] +3.0≦[Al] １／１０ｔ -[Al] ｓ ≦+13.0 (In the above relational expression 2, the [Al] １／１０ｔ It is 1 in the thickness direction from the surface of the plating layer / Represents the weight % Al content at the 10t position (where t is the total thickness of the plating layer), and the above [A l] ｓ (This represents the weight percentage content of Al on the surface of the plating layer.)

2. Fe-Al suppression is provided between the base steel sheet and the Zn-Mg-Al plating layer. A plated steel sheet according to claim 1, further comprising a layer.

3. The aforementioned plating layer consists of Mg: 4.0-7.0% by weight, Al: 8.2-19.5%, and the remainder The plated steel sheet according to claim 1, comprising part Zn and other unavoidable impurities.

4. The plated steel sheet according to claim 1, further satisfying the following relational expression 3. [Relationship Equation 3] -1.0≦[Mg] １／１０ｔ -[Mg] ｓ ≦+1.0 (In the above relational expression 3, the [Mg] １／１０ｔ It is 1 in the thickness direction from the surface of the plating layer / Represents the weight % content of Mg at the 10t position (where t is the total thickness of the plating layer), and the above [M g] ｓ (This represents the weight percentage content of Mg on the surface of the plating layer.)

5. The weight percentage of Mg at a position 2 / 3t in the thickness direction from the surface of the aforementioned plating layer is The material according to claim 1 satisfies ±0.5% by weight relative to the average weight percentage content of Mg in the layer. Steel plate.

6. The area ratio of the Al phase on the surface of the aforementioned plating layer, in which the Zn solid solution rate is 27 atomic percent or more, is 2.0 to The plated steel sheet according to claim 1, wherein the content is 10.1%.

7. In a shot blast cabin where metal material circulates at a rotational speed of 1200-2000 mph For the advancing steel plate, metal balls with a particle size of 0.6 to 1.0 mm are applied at 400 to 1200 kJ. This is the stage in which primary shot blasting is performed, projecting the blast onto the surface of the base steel sheet at a rate of g / min. ； In a shot blast cabin where metal material circulates at a rotational speed of 1200-2000 mph For the advancing steel plate, metal balls with a particle size of 0.2 to 0.5 mm are applied at 400 to 1200 kJ. This is the stage where secondary shot blasting is performed, projecting the blast onto the surface of the base steel sheet at a rate of g / min. ； The aforementioned shot-blasted steel sheet contains, by weight %, Mg: 4.0-7.0%, Al : Contains 8.2–19.5%, with the remainder being Zn and other unavoidable impurities, and solidifies on the equilibrium phase diagram. The device is immersed in a plating bath maintained at a temperature of Ts + 20°C to Ts + 80°C relative to the starting temperature (Ts). The stage of dipping and hot-dip galvanizing; and The aforementioned hot-dip galvanized steel sheet is subjected to a process of 2 to 8°C / s from the solidification start temperature to the solidification end temperature. A method for manufacturing plated steel sheets, comprising the step of cooling with an inert gas at a uniform cooling rate.

8. Before performing the hot-dip galvanizing, the surface roughening of the shot-blasted base steel sheet is performed. Roll reduction of 100 to 400 tons using a dull roll with Ra of 1.8 to 2.8 μm. The plated steel sheet according to claim 7, further comprising the step of performing pre-temper rolling to apply a certain substance to the surface of the steel sheet. A method for manufacturing this product.

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