Plated steel material

Abstract

Adopted is a plated steel material, wherein: a plating layer has an average chemical composition comprising, by mass%, more than 50.00% of Zn, more than 15.0% but less than 30.0% of Al, more than 5.0% but less than 15.0% of Mg, 0.25% to less than 3.50% of Si, and impurities; the total amount (ΣA) of at least one kind selected from the group consisting of Sn, Bi, and In is less than 1.00%; the total amount (ΣB) of at least one kind selected from the group consisting of Ca, Y, La, Ce, and Sr is 0.02% to less than 0.60%; 2.0 ≤ Mg / Si < 20.0 (expression 1), 3.0 ≤ Si / ΣB < 24.0 (expression 2), and 26.0 ≤ (Si / ΣB) x (Mg / Si) < 375.0 (expression 3) are satisfied; and in an X-ray diffraction pattern of the plating layer surface, a diffraction intensity ratio R1 as defined by R1 = {I (16.18˚) + I (32.69˚)} / I (27.0˚) (expression 4) satisfies 2.5 < R1 (expression 5).

Description

Plated steel

[0001] The present invention relates to a plated steel material. This application claims priority to Japanese Patent Application No. 2021-005575, filed on January 18, 2021, the contents of which are incorporated herein by reference.

[0002] Many metal materials are used as building materials. In particular, high-quality metal materials such as titanium, stainless steel, and aluminum are used for exterior, wall, and roofing materials, which are used for a long time. These materials generally have a passive film on the metal surface, making them resistant to corrosion and their appearance changes little over the long term in outdoor environments. However, they are very expensive, and construction costs tend to be high.

[0003] On the other hand, because iron is relatively inexpensive, zinc-plated steel sheets, aluminum-plated steel sheets, Galvalume steel sheets (registered trademark), and other iron-based materials are used as building materials. Among these, aluminum-plated steel sheets have, for example, an aluminum layer or an aluminum-zinc alloy layer about 20 μm thick on the surface of the steel sheet. Since there is a large amount of aluminum on the outermost surface compared to the base iron, they have little sacrificial corrosion protection like zinc-plated steel sheets. Therefore, aluminum-plated steel sheets require corrosion protection treatment in areas where the steel sheet (base steel) is exposed, such as processed sections and cut edges. In addition, in salt-damaged areas, there is a risk of the aluminum passive film breaking down, leading to further corrosion. Furthermore, aluminum-plated steel sheets are unsuitable for use in environments where alkaline wastewater is discharged, such as cowsheds and pigpens.

[0004] These problems can be somewhat solved by using highly corrosion-resistant zinc-based plated steel sheets, such as those described in Patent Documents 1 and 2, or Patent Document 3. However, zinc-based plated steel sheets have a higher sacrificial corrosion protection effect than aluminum-based plated steel sheets, and therefore the occurrence of white rust and discoloration due to corrosion are more noticeable. Therefore, zinc-based plated steel sheets tend not to maintain the beautiful appearance over a long period of time that is expected of aluminum-plated steel sheets or Galvalume steel sheets (registered trademark).

[0005] In order to maintain the appearance for a long period of time, it is conceivable to apply a color painting treatment to the zinc-plated steel sheet. However, the painting treatment may cause the loss of the metallic luster of the zinc-plated steel sheet itself, increase costs due to an increase in the number of processes, and cause color fading due to paint peeling and a decrease in weather resistance. Therefore, there is a demand for zinc-plated steel materials that are rich in sacrificial corrosion protection, highly versatile, and can maintain metallic luster for a long period of time.

[0006] Japanese Patent Application Laid-Open No. 10-226865 International Publication No. 2000 / 71773 International Publication No. 2018 / 139619

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a zinc-based plated steel material that exhibits little change in appearance over a long period of time.

[0008] In order to solve the above problems, the present invention employs the following configuration. [1] A plated steel material having a plating layer on a steel material surface, wherein the plating layer has an average chemical composition, in mass%, of: Zn: more than 50.00%, Al: more than 15.0% and less than 30.0%, Mg: more than 5.0% and less than 15.0%, Si: 0.25% or more and less than 3.50%, Sn: 0% or more and less than 1.00%, Bi: 0% or more and less than 1.00%, In: 0% or more and less than 1.00%, Ca: 0% or more and less than 0.60%, Y: 0% or more and less than 0.60%, La: 0% or more and less than 0.60%, Ce: 0% or more and less than 0.60%, Sr: 0% or more and less than 0.60%, Cr: 0% or more and less than 0.25%, Ti: 0% or more and less than 0.25%, Ni: 0% or more and less than 0.25%, Co: 0% or more and less than 0.25%, V: 0% or more and less than 0.25%, Nb: 0% or more and less than 0.25%, Zr: 0% or more and less than 0.25%, Mo: 0% or more and less than 0.25%, W: 0% or more and less than 0.25%, Ag: 0% or more and less than 0.25%, Cu: 0% or more and less than 0.25%, Mn: 0% or more and less than 0.25%, Fe: 0% or more and less than 5.0%, Sb: 0% or more and less than 0.5%, Pb: 0% or more and less than 0.5%, B: 0% or more and less than 0.5%, P: 0% or more and less than 0.5%, and impurities, wherein the total amount (ΣA) of at least one element selected from the group consisting of Sn, Bi and In is less than 1.00%, a plated steel material in which the total amount (ΣB) of at least one element selected from the group consisting of Ca, Y, La, Ce, and Sr is 0.02% or more and less than 0.60%, the Mg content, the Si content, and the ΣB satisfy the following formulas 1 to 3, and in an X-ray diffraction pattern of the plated layer surface, measured using Cu-Kα radiation at an X-ray output of 40 kV and 150 mA, a diffraction intensity ratio R1 defined by the following formula 4 satisfies the following formula 5:2.0≦Mg / Si<20.0 ...Equation 1 3.0≦Si / ΣB<24.0...Equation 2 26.0≦(Si / ΣB)×(Mg / Si)<375.0...Equation 3 R1={I(16.18°)+I(32.69°)} / I(27.0°) ...Equation 4 2.5<R1...Equation 5 wherein Si and Mg in Equations 1 to 3 are the average compositions (mass%) of Si and Mg in the plating layer, and I(16.18°) in Equation 4 is the diffraction intensity (cps) at 2θ=16.18° in the X-ray diffraction pattern, I(32.69°) is the diffraction intensity (cps) at 2θ=32.69° in the X-ray diffraction pattern, and I(27.0°) is the diffraction intensity (cps) at 2θ=27.0° in the X-ray diffraction pattern. When a diffraction peak with an intensity of 1000 cps or more appears at 2θ=27.0°, I(27.0°) is set to 585 cps. [2] The plated steel material according to [1], wherein, in an X-ray diffraction pattern of the plated layer surface measured using Cu-Kα radiation at an X-ray output of 40 kV and 150 mA, a diffraction intensity ratio R2 defined by the following formula 6 satisfies the following formula 7: R2 = {I(24.24°) + I(28.07°)} / I(27.0°) ... Equation 6 2.5 < R2 ... Equation 7 In Equation 6, I(24.24°) is the diffraction intensity (cps) at 2θ = 24.24° in the X-ray diffraction pattern, I(28.07°) is the diffraction intensity (cps) at 2θ = 28.07° in the X-ray diffraction pattern, and I(27.0°) is the diffraction intensity (cps) at 2θ = 27.0° in the X-ray diffraction pattern. Note that when a diffraction peak with an intensity of 1000 cps or more appears at 2θ = 27.0°, I(27.0°) in Equation 6 is set to 585 cps. [3] The plated steel product according to [1] or [2], wherein R1 defined by Equation 4 satisfies the following Equation 8: 10<R1 ... Formula 8 [4] The plated steel material according to any one of [1] to [3], which satisfies the following formula 9: 3.0≦Si / ΣA<50.0 ... Formula 9 wherein Si in formula 9 is the average composition (mass%) of Si in the plated layer.

[0009] According to the present invention, it is possible to provide a zinc-based plated steel product that exhibits little change in appearance over a long period of time, particularly when used outdoors, and that has beautiful appearance over a long period of time.

[0010] FIG. 2 is an X-ray diffraction diagram of the surface of the plating layer of the plated steel material according to the embodiment of the present invention.

[0011] Among Zn-based plated steel materials, Zn-Al-Mg-based plated steel materials, which are typified by highly corrosion-resistant plating, have a high sacrificial corrosion protection effect, and as corrosion occurs, a thin rust layer gradually forms on the surface of the plated layer. For this reason, when Zn-Al-Mg-based plated steel materials are used in outdoor environments, they are difficult to maintain their metallic luster, and some changes in appearance from when they were first applied are observed, such as a loss of metallic luster within about one year after application. The cause of the change in appearance of Zn-Al-Mg-based plated steel materials is the formation of a passive film (Al) like an Al-based plated layer. ２ O ３ This is because the passive layer is not sufficiently formed on the surface of the plating layer, and the surface of the plating layer is prone to corrosion in areas where there is no passive layer, causing changes in appearance. In other words, plating layers with high sacrificial corrosion protection have the opposite characteristics of being prone to elution, corrosion, and changes in appearance.

[0012] Among Zn-based plated steel materials, for example, Galvalume Steel Sheet (registered trademark) contains a large amount of Al in the Zn plated layer, so it is possible to form a passivation film to some extent on the surface of the plated layer, but on the other hand, the amount of Zn is relatively reduced by the large amount of Al contained, and sacrificial corrosion protection is almost lost. In other words, a plated layer that is difficult to change in surface appearance has the opposite effect of weak sacrificial corrosion protection.

[0013] Therefore, we have investigated whether the appearance change of the plating layer during corrosion can be suppressed by adding a compound to the plating layer that forms a passive film on the surface of the plating layer while maintaining a low Al concentration in the plating layer. It is expected that a plating layer containing a large amount of such a compound will form a dense oxide film on the surface, making it less likely to change in appearance during corrosion (maintaining the metallic luster of the plated metal). After extensive research, the present inventors have found that in the case of Zn-Al-Mg-plated steel, a dense oxide film can be formed by adding a Si-based compound to the plating layer. However, when Si and Mg coexist in a Zn-based plating layer, Mg ２ Compounds that do not contribute to the formation of oxide films, such as Si, are produced, inhibiting the production of Si-based compounds that contribute to the formation of oxide films. ２ It is necessary to control the Si to have an appropriate precipitate form.

[0014] On the other hand, Mg ２ Si increases the sacrificial corrosion resistance because Mg bonds to Si in large amounts, and generally makes the appearance more susceptible to change. ２ Since Si itself is a substance that contributes to sacrificial corrosion protection, it is an intermetallic compound that promotes blackening itself, but if the deposition form is controlled, it will corrode uniformly and also have the effect of preventing the so-called blackening, in which the surface of the plating layer turns black due to the oxide film that Si forms at the same time. ２ The present inventors have discovered a component composition of the plating layer and a method for forming the plating layer that enable a sufficient formation of a dense oxide film on the surface without reducing the effect of preventing blackening due to Si.

[0015] A plated steel material according to an embodiment of the present invention is a plated steel material having a plating layer on a steel surface, and the plating layer has an average chemical composition, in mass%, of Zn: more than 50.00%, Al: more than 15.0% and less than 30.0%, Mg: more than 5.0% and less than 15.0%, Si: 0.25% or more and less than 3.50%, Sn: 0% or more and less than 1.00%, Bi: 0% or more and less than 1.00%, In: 0% or more and less than 1.00%, Ca: 0% or more and less than 0.60%, Y: 0% or more and less than 0.60%, La: 0% or more and less than 0.60%, Ce: 0% or more and less than 0.60%, Sr: 0% or more and less than 0.60%, Cr: 0% or more and less than 0.25%, Ti: 0% or more and less than 0.25%, Ni: 0% or more and less than 0.25%, Co: 0% or more and less than 0.25%, V: 0% or more and less than 0.25%, Nb: 0% or more and less than 0.25%, Zr: 0% or more and less than 0.25%, Mo: 0% or more and less than 0.25%, W: 0% or more and less than 0.25% 0.25%, Ag: 0% or more and less than 0.25%, Cu: 0% or more and less than 0.25%, Mn: 0% or more and less than 0.25%, Fe: 0% or more and less than 5.0%, Sb: 0% or more and 0.5% or less, Pb: 0% or more and 0.5% or less, B: 0% or more and 0.5% or less, P: 0% or more and 0.5% or less, and impurities, the total amount (ΣA) of at least one selected from the group consisting of Sn, Bi and In is less than 1.00%, Ca, The plated steel material has a total content (ΣB) of at least one element selected from the group consisting of Y, La, and Ce of 0.02% or more and less than 0.60%, the Mg content, the Si content, and the ΣB satisfy the following formulas 1 to 3, and in an X-ray diffraction pattern of the plated layer surface measured using Cu-Kα radiation at an X-ray output of 40 kV and 150 mA, the diffraction intensity ratio R1 defined by the following formula 4 satisfies the following formula 5:

[0016] 2.0≦Mg / Si<20.0...Formula 1 3.0≦Si / ΣB<24.0...Formula 2 26.0≦(Si / ΣB)×(Mg / Si)<375.0...Formula 3 R1={I(16.18°)+I(32.69°)} / I(27.0°)...Formula 4 2.5<R1...Formula 5

[0017] where Si and Mg in Formulas 1 to 3 are the average compositions (mass%) of Si and Mg in the plating layer, and I(16.18°) in Formula 4 is the diffraction intensity at 2θ=16.18° in the X-ray diffraction pattern, I(32.69°) is the diffraction intensity at 2θ=32.69° in the X-ray diffraction pattern, and I(27.0°) is the diffraction intensity at 2θ=27.0° in the X-ray diffraction pattern. Note that when a diffraction peak with an intensity of 1000 cps or more appears at 2θ=27.0°, I(27.0°) in Formula 4 is set to 585 cps.

[0018] In the following description, the "%" used to indicate the content of each element in the chemical composition means "% by mass." Furthermore, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0019] Furthermore, when the numerical range described before or after "to" is followed by "greater than" or "less than," the numerical range does not include the numerical value as the lower limit or upper limit. Furthermore, the components of the following embodiments can be combined with each other.

[0020] Furthermore, "corrosion resistance" refers to the property of the plating layer itself that makes it difficult for the plating layer to corrode. Note that the plating layer according to this embodiment has a sacrificial corrosion protection effect on the steel material, and therefore, the corrosion process involves a process in which the plating layer corrodes and turns into white rust before the steel material corrodes, and then, after the white-rusted plating layer disappears, the steel material corrodes and turns into red rust.

[0021] The passive film present on the surface of the plating layer according to this embodiment is an oxide film, but its thickness is less than 1 μm at most, and is often only a few nanometers, making it difficult to confirm its presence or absence using an SEM (reflection electron microscope). It is presumed that its formation can be ascertained using a TEM (transmission electron microscope) or XPS analysis, but both TEM and XPS have a narrow observation field and pose problems with quantitative analysis. For this reason, in this embodiment, the presence of the film is indirectly confirmed by identifying the compounds involved in the formation of the oxide film using X-ray diffraction.

[0022] First, the steel material to be plated will be described. There are no particular limitations on the shape of the steel material, and the steel material may be a steel plate, a steel pipe, a civil engineering / construction material (such as a fence or culvert, a corrugated pipe, a drainage ditch cover, a sand-fly prevention board, a bolt, a wire mesh, a guardrail, a water cut-off wall, etc.), a prefabricated member, a residential wall, a roofing material, a home appliance member (such as a housing for an outdoor unit of an air conditioner), an automobile outer panel, an automobile part (such as an undercarriage member), etc., or may be a material for a steel structural member that is subjected to welding and formed.

[0023] There are no particular limitations on the material of the base steel sheet. Examples of applicable steel materials include general steel, Ni-preplated steel, Al-killed steel, extra-low carbon steel, high carbon steel, various high-tensile steels, and some high-alloy steels (steels containing corrosion-resistant strengthening elements such as Ni and Cr). Furthermore, the steel materials are not particularly limited in terms of the manufacturing method of the steel material, the manufacturing method of the steel sheet (hot rolling, pickling, cold rolling, etc.). Furthermore, pre-plated steel materials may be used, which are pre-plated with a plating layer of less than 1 μm of Zn, Ni, Sn, or an alloy thereof.

[0024] Next, the plating layer will be described. The plating layer according to this embodiment includes a Zn-Al-Mg alloy layer. Adding alloy elements such as Al and Mg to Zn improves corrosion resistance, so a thin film, for example, about half the thickness of a typical Zn plating layer, can provide equivalent corrosion resistance. Similarly, the present invention also ensures corrosion resistance equivalent to or greater than that of a Zn plating layer with a thin film. The plating layer may also include an Al-Fe alloy layer.

[0025] The Zn—Al—Mg alloy layer is made of a Zn—Al—Mg alloy, which means a ternary alloy containing Zn, Al, and Mg. The Al—Fe alloy layer is an interface alloy layer between the steel material and the Zn—Al—Mg alloy layer.

[0026] That is, the plating layer may have a single-layer structure of a Zn—Al—Mg alloy layer, or a laminated structure including a Zn—Al—Mg alloy layer and an Al—Fe alloy layer. In the case of a laminated structure, the Zn—Al—Mg alloy layer is preferably the layer that constitutes the surface of the plating layer. On the outermost surface of the plating layer, an oxide film is formed by oxidation of the plating layer constituent elements, and has a thickness of less than 1 μm. This oxide film has high barrier properties and high corrosion resistance, so the plating layer maintains its metallic luster and is less susceptible to changes in appearance.

[0027] In the case of conventional Galvalume steel sheets (registered trademark), the Zn plating layer contains a large amount of Al, and the Al phase on the surface of the plating layer forms an oxide film, resulting in a highly corrosion-resistant plating layer. On the other hand, Zn, Mg, and other elements contained in the plating layer of this embodiment are also elements that form a passivation film. However, since these metals are relatively more active than Al, the passivation film formed from Zn and Mg has low barrier properties and is easily damaged unless a sufficient thickness is ensured. Therefore, passivation films formed from Zn and Mg are generally prone to corrosion and appearance changes. Therefore, in plating layers with a low Al concentration, Zn- and Mg-based passivation films are mainly formed, and some kind of treatment is required to improve the barrier properties. The oxide film formed on the surface of the plating layer of the plated steel material according to this embodiment is Al, an oxide of Al contained in the plating layer. ２ O ３ In addition, it is presumed that the coating layer is composed of Al-Si-O based intermetallic compounds, which provide high corrosion resistance and little change in appearance.

[0028] When an Al-Fe alloy layer is present in the plating layer, the Al-Fe alloy layer bonds the steel material to the Zn-Al-Mg alloy layer. The thickness of the interface alloy layer including the Al-Fe alloy layer can be controlled in any way by adjusting the plating bath temperature and plating bath immersion time during the production of the plated steel material. In hot-dip galvanized steel sheet manufacturing methods centered on the Sendzimir process, the Zn-Al-Mg alloy layer is the main component of the plating layer, and the thickness of the Al-Fe alloy layer is sufficiently small, so it has little effect on the corrosion resistance of the plating layer. Furthermore, since the Al-Fe alloy layer is formed near the interface, it has almost no effect on the corrosion resistance in the early stages of corrosion or in the appearance of the plating layer.

[0029] The Al-Fe alloy layer is formed on the surface of the steel material (specifically, between the steel material and the Zn-Al-Mg alloy layer), and has an Al structure. ５ The Fe phase is the main phase layer. The Al-Fe alloy layer is formed by mutual atomic diffusion between the base steel (steel material) and the coating bath. When hot dip coating is used as the manufacturing method, an Al-Fe alloy layer is likely to be formed in the coating layer containing Al. Since the coating bath contains Al at a certain concentration or more, ５ The Fe phase is formed most frequently. However, atomic diffusion takes time, and there are also areas where the Fe concentration is high near the base steel. Therefore, the Al-Fe alloy layer is partially composed of AlFe phase, Al ３ Fe phase, Al ５ Fe ２ In some cases, the Al-Fe alloy layer contains a small amount of Zn, because the plating bath contains a certain concentration of Zn.

[0030] The plating layer according to this embodiment contains Si, which is particularly likely to be incorporated into an Al-Fe alloy layer, and may form an Al-Fe-Si intermetallic compound phase. Identified intermetallic compound phases include the AlFeSi phase, and isomers include α-, β-, q1-, and q2-AlFeSi phases. Therefore, these AlFeSi phases may be detected in the Al-Fe alloy layer. An Al-Fe alloy layer containing these AlFeSi phases is also referred to as an Al-Fe-Si alloy layer.

[0031] The thickness of the entire plating layer is affected by the plating conditions, so there are no particular upper or lower limits for the thickness of the entire plating layer. In particular, changes in appearance over time during outdoor use in an atmospheric environment are only affected by the state of the plating layer in the surface layer of a few micrometers, and are not significantly affected by its thickness, because corrosion of the plating layer is very slow. Furthermore, for example, the thickness of the entire plating layer is related to the viscosity and specific gravity of the plating bath in conventional hot-dip plating methods. Furthermore, the amount of plating weight is adjusted by the drawing speed of the steel material (base steel) and the strength of wiping.

[0032] Next, the average chemical composition of the plating layer will be described. When the plating layer has a single-layer structure of a Zn—Al—Mg alloy layer, the average chemical composition of the entire plating layer is the average chemical composition of the Zn—Al—Mg alloy layer. When the plating layer has a laminated structure of an Al—Fe alloy layer and a Zn—Al—Mg alloy layer, the average chemical composition is the combined average chemical composition of the Al—Fe alloy layer and the Zn—Al—Mg alloy layer.

[0033] Typically, in hot-dip galvanizing, the chemical composition of the Zn—Al—Mg alloy layer is almost identical to that of the plating bath because the formation reaction of the plating layer is almost always completed within the plating bath. Furthermore, in hot-dip galvanizing, the Al—Fe alloy layer is instantaneously formed and grows immediately after immersion in the plating bath. The formation reaction of the Al—Fe alloy layer is completed within the plating bath, and its thickness is often sufficiently smaller than that of the Zn—Al—Mg alloy layer. Therefore, unless special heat treatment such as a thermal alloying treatment is performed after plating, the average chemical composition of the entire plating layer is substantially identical to that of the Zn—Al—Mg alloy layer, and components such as the Al—Fe alloy layer can be ignored.

[0034] The elements contained in the plating layer will be described below. In this embodiment, the component composition of the plating layer is important for sufficient formation of Al-Si-O intermetallic compounds. If the component composition of the plating layer is out of the range described below, other compounds than Al-Si-O compounds, such as Al-Ca-Si compounds or Mg ２Compounds such as Si that are not involved in the formation of an oxide film containing Si on the surface of the plating layer are preferentially obtained, making it impossible to obtain the desired performance.

[0035] Zn: More than 50.00% The plated steel material according to this embodiment is a highly versatile Zn-based plated steel material, and contains a certain amount of Zn or more to ensure sacrificial corrosion protection. This provides the steel material with appropriate sacrificial corrosion protection. For example, even in an environment where a cut edge of 1.6 mm or more is exposed, a Zn content of more than 50.00% provides sufficient sacrificial corrosion protection at the cut edge, maintaining high corrosion resistance. If the Zn content is 50.00% or less, corrosion resistance may be poor depending on the thickness of the plating layer, such as when the cut edge is exposed. Therefore, the Zn content is set to more than 50.00%. Preferably, the Zn content is 65.00% or more, more preferably more than 70.00%. The upper limit of the Zn content does not need to be particularly limited, but since a high Zn content relatively reduces the contents of other alloying elements, it may be set to, for example, 80.00% or less.

[0036] Al: more than 15.0% but less than 30.0% Like Zn, Al is an element that mainly constitutes the coating layer. In Zn-Al-Mg coatings, Al mainly forms an Al phase in the coating layer. The Al phase is also present on the surface of the coating layer, and around the Al phase, ２ O ３ However, the amount of Al phase contained in the plating layer according to this embodiment is insufficient to form an oxide film that covers the entire surface of the plating layer. That is, if the Al content is 15.0% or less, the Al content is insufficient to form Al-Si-O compounds, which are compounds that form an oxide film, and the Al-Si-O compounds cannot be detected in the plating layer. On the other hand, if the Al content is 30.0% or more, as described above, the sacrificial corrosion protection property decreases, so the Al content is set to less than 30.0%. The preferred Al content is 17.0% or more, or 20.0% or more, and the preferred Al content is 29.0% or less or 25.0% or less.

[0037] Mg: more than 5.0% and less than 15.0% Mg is an element that has a sacrificial corrosion protection effect and enhances corrosion resistance. The high corrosion resistance and high sacrificial corrosion protection of the plated steel material according to this embodiment are achieved by the inclusion of Mg. If the Mg content is insufficient, the sacrificial corrosion protection effect decreases and the corrosion resistance tends to decrease, so the lower limit is set to more than 5.0%. On the other hand, if the Mg content is 15.0% or more, the Al content in the plated layer becomes relatively low, and an Al phase is not formed on the surface of the plated layer, the oxide film becomes unstable, and the appearance deteriorates significantly during corrosion. This is because the Al phase decreases relatively, but the MgZn ２ This is because a large amount of the magnesium phase is formed on the surface of the coating layer. Al-Si-O-based compounds are also not formed. Therefore, the magnesium content is set to less than 15.0%. The magnesium content is preferably 5.1% or more, or 6.0% or more, and more preferably 13.0% or less, or 12.5% ​​or less.

[0038] Si: 0.25% or more but less than 3.50% Si inhibits the growth of the Al-Fe alloy layer and improves corrosion resistance. When present in trace amounts, Si forms Al-Ca-Si compounds and other compounds, and also forms an interstitial solid solution in the Al-Fe alloy layer. The formation of an Al-Fe-Si intermetallic compound phase in the Al-Fe alloy layer has already been explained above. If Si is incorporated into these compounds, it does not produce any change in the performance of the coating layer. Therefore, if the Si content is less than 0.25%, most of the Si is trapped in these compounds, which does not result in any changes in the appearance of the coating layer, sacrificial corrosion protection, or other performance changes such as corrosion resistance. Therefore, the Si content is set to 0.25% or more. Furthermore, if Si exceeds its lower limit, it forms Al-Si-O compounds in the coating layer. These Al-Si-O compounds are formed by the Al-Si-O compounds derived from the Al in the coating layer. ２ O ３ At the same time, a strong oxide film is formed, which prevents deterioration in the appearance of the plating layer. Therefore, the Si content is preferably set to 0.25% or more, more preferably set to 0.50% or more, and even more preferably set to 0.60% or more.

[0039] On the other hand, excess Si causes coarse Mg ２ Forms intermetallic compounds such as Si. Coarse Mg２ Si is very easy to dissolve and improves sacrificial corrosion protection, but Mg ２ If Si remains coarse and dispersed in the plating layer, corrosion can easily reach the plating layer surface and interface, and further, the Zn-Al-MgZn ２ The formation of a ternary eutectic structure is promoted, and the proportion of the basic constituent phases for maintaining the corrosion resistance of the flat surface is adversely affected, so that the corrosion resistance of the flat surface is slightly deteriorated. ２ The formation of intermetallic compound phases such as Si phases reduces the effects of elements such as Ca and Y, and tends to negate the effects of elements such as Ca, which are normally added in small amounts to produce effects. Furthermore, excessive Si may bond with other elements in the plating layer in various ways, resulting in insufficient sacrificial corrosion protection performance. Therefore, the Si content is set to less than 3.50%. From the viewpoints of flat surface corrosion resistance and sacrificial corrosion protection, the Si content may preferably be 3.00% or less, 2.50% or less, 2.00% or less, 1.50% or less, or 1.30% or less.

[0040] In addition, when the Si content is in the range of 0.25% or more and less than 3.50%, the Mg ２ The finely dispersed Si can enhance sacrificial corrosion protection and improve the blackening prevention effect of the plating layer without adversely affecting the appearance change of the Al-Si-O based compound. From the viewpoint of preventing blackening, the Si content is preferably 0.40% or more, and more preferably 0.80% or less.

[0041] Formula 1: 2.0≦Mg / Si<20.0 Mg and Si react very easily. ２ However, since the ratio of the Mg and Si contents has a significant effect on the properties of the plating layer, it is necessary to set the ratio of the Mg and Si contents (Mg / Si) within an appropriate range. ２ However, if the Mg / Si ratio becomes too large (if there is too much Mg relative to Si), the Mg that contributes to improving sacrificial corrosion protection will be formed. ２The decrease in Si content makes it difficult to form the coating, which may reduce the sacrificial corrosion protection of the plating layer. Furthermore, the lack of Si makes it impossible to expect the effects of an oxide film, resulting in significant changes in the appearance of the plating layer. Furthermore, if the Mg / Si ratio is too low, a large amount of Al—Si—O-based compounds will form in the plating layer, and these Al—Si—O-based compounds will adhere to the surface of the plating layer in a granular form, worsening the appearance of the plating layer and further reducing the corrosion resistance of the plating layer. Furthermore, Si will combine with various other additive elements in the plating layer, making it difficult to maintain the properties of the plating layer. Therefore, the Mg / Si ratio is set to 2.0 or more, more preferably 6.0 or more, and even more preferably 8.0 or more. The Mg / Si ratio is set to less than 20.0, more preferably 16.0 or less, and even more preferably 12.0 or less.

[0042] Element Group A (Sn: 0% or more and less than 1.00%, Bi: 0% or more and less than 1.00%, In: 0% or more and less than 1.00%, total amount of element group A (ΣA): less than 1.00%) Element group A is an element (Sn, Bi, In) that can be optionally contained. The inclusion of at least one element selected from element group A improves sacrificial corrosion protection. Each element of element group A forms a compound with Mg in the plating layer. This compound is easily dissolved by moisture, etc., and easily dissolves Mg, thereby imparting sacrificial corrosion protection. By containing 0.01% or more of each element, the improved effect of sacrificial corrosion protection can be confirmed, for example, at a cut end surface of a plate with a thickness of 1.6 mm. However, excessive inclusion of these elements improves the sacrificial corrosion protection of the plating layer, making the plating layer more susceptible to dissolution, adversely affecting the corrosion resistance of flat portions, etc. Furthermore, the appearance of the plating layer is likely to change. Therefore, the content of each element of element group A is set to less than 1.00%. The total amount (ΣA) of element group A is also set to less than 1.00%. If ΣA is 1.00% or more, the appearance of the plating layer is likely to change.

[0043] Furthermore, by containing the element group A which improves the sacrificial corrosion protection, it is possible to suppress the decrease in the sacrificial corrosion protection due to the formation of Al—Si—O oxides. ２ O ３ This Al forms an oxide film with excellent insulating properties. ２ O３ The oxide film of Al has excellent barrier properties. Although Al is an element exhibiting a base potential, its oxide film has high barrier properties, which reduces sacrificial corrosion protection. When an Al-Si-O compound is added as a constituent material of the oxide film, the barrier effect of the oxide film becomes excessively high, resulting in a reduction in sacrificial corrosion protection. Therefore, by including element group A, it is possible to compensate for the reduction in sacrificial corrosion protection that accompanies the formation of the oxide film, and obtain a plating layer that is resistant to appearance changes while maintaining sacrificial corrosion protection.

[0044] Element Group B (Ca: 0% or more and less than 0.60%, Y: 0% or more and less than 0.60%, La: 0% or more and less than 0.60%, Ce: 0% or more and less than 0.60%, Sr: 0% or more and less than 0.60%, total amount of element group B (ΣB): 0.02% or more and less than 0.60%) The elements of element group B (Ca, Y, La, Ce, Sr) are optional elements. By containing at least one element selected from element group B together with Mg, corrosion resistance and sacrificial corrosion protection tend to be slightly improved. However, if these elements are contained in excess, an intermetallic compound phase consisting mainly of each element is formed, hardening the plating layer and causing cracks during processing of the plating layer, which may then cause powdering peeling. Therefore, the content of each of these elements is preferably less than 0.60%. The content of each element may be 0.01% or more, or may be 0.02% or more.

[0045] Furthermore, if the total amount of element group B is too large, granular substances adhere to the plating surface, deteriorating the properties of the plating. Therefore, the total amount of these elements (ΣB) is set to less than 0.60%. Furthermore, if the total amount of these elements (ΣB) is too small, Al-Si-O-based compounds are not formed in the plating layer. Furthermore, the elements of element group B are Mg, which is inherently prone to precipitate in agglomerates. ２ Reduce the stability of Si and ２Si has the effect of finely dispersing and precipitating, so a delicate balance of components is required, which can suppress blackening of the coating layer. Therefore, the total amount of element group B (ΣB) is set to 0.02% or more. If the total amount ΣB is less than 0.02%, the desired performance, such as appearance, cannot be obtained. The total amount of element group B (ΣB) may be 0.04% or more, and the total amount of element group B (ΣB) may be 0.50% or less, or 0.30% or less.

[0046] Formula 2: 3.0≦Si / ΣB<24.0 When the ratio (Si / ΣB) of the Si content to the total amount (ΣB) of elements contained in element group B is 24.0 or more (when Si is too much and element group B is too little), Mg in the coating layer is formed as coarse Mg ２ However, the bonding reaction between Mg and Si cannot be suppressed to the extent that Al-Si-O compounds are sufficiently formed, and the effect of forming Al-Si-O compounds by element group B cannot be obtained. ２ Si also cancels the effect of Al-Si-O oxides, so that no diffraction peaks due to Al-Si-O compounds appear, and the effect of suppressing changes in the appearance of the plating layer cannot be obtained.

[0047] Furthermore, when Si / ΣB is less than 3.0 (when Si is too little and element group B is too much), Ca, Al, and Si bond to form Al-Ca-Si compounds, etc., and Al-Si-O compounds are not sufficiently produced. Therefore, when the plating layer surface is subjected to X-ray diffraction analysis, no diffraction peaks due to Al-Si-O compounds appear, and the effect of suppressing changes in the appearance of the plating layer cannot be obtained. As mentioned above, Si is trapped in the compounds and interfaces, and does not cause any changes to the plating layer. Therefore, Si / ΣB is set to be 3.0 or more and less than 24.0. Si / ΣB is preferably 4.0 or more, more preferably 5.0 or more. Si / ΣB is preferably 10.0 or less, more preferably 8.0 or less.

[0048] Formula 3: 26.0≦(Si / ΣB)×(Mg / Si)<375.0 When both Formula 1 and Formula 2 are satisfied, the conditions for the formation of Al-Si-O based compounds are met. However, near the upper and lower limit values ​​of Formula 1 and Formula 2, depending on the composition of the constituent elements other than Mg, Si, and element group B of the coating layer, the formation of Mg may be more important than the formation of Al-Si-O based compounds. ２ In some cases, the formation of Si or Al—Ca—Si compounds may predominate. Therefore, as a condition for ensuring that the formation of Al—Si—O compounds predominates, (Si / ΣB)×(Mg / Si) is set to a range of 26.0 or more and less than 375.0. (Si / ΣB)×(Mg / Si) is the product of Si / ΣB in Equation 2 and Mg / Si in Equation 1. To stably obtain Al—Si—O compounds, the lower limit of this product must be 26.0 or more. If this product is less than 26.0, the formation of Al—Si—O compounds becomes unstable, and desired performance, such as maintaining the appearance of the coating layer or improving corrosion resistance, may not be achieved. For the same reason, the upper limit must also be less than 375.0. More preferably, (Si / ΣB)×(Mg / Si) is 30.0 or more, and even more preferably 35.0 or more. More preferably, (Si / ΣB)×(Mg / Si) is 200.0 or less, and even more preferably 100.0 or less.

[0049] Element group C (Cr: 0% or more and less than 0.25%, Ti: 0% or more and less than 0.25%, Ni: 0% or more and less than 0.25%, Co: 0% or more and less than 0.25%, V: 0% or more and less than 0.25%, Nb: 0% or more and less than 0.25%, Zr: 0% or more and less than 0.25%, Mo: 0% or more and less than 0.25%, W: 0% or more and less than 0.25%, Ag: 0% or more and less than 0.25%, Cu: 0% or more and less than 0.25%, Mn: 0% or more and less than 0.25%, Fe: 0% or more and less than 5.0%) Of the elements in element group C, the elements except Fe are metal elements that can be optionally contained in the plating layer. The inclusion of these elements (Cr, Ti, Ni, Co, V, Nb, Zr, Mo, W, Ag, Cu, and Mn) has the effect of improving the flat corrosion resistance of the coating layer. A clear improvement in corrosion resistance is confirmed when the content is 0.10% or more, so it is preferable to include 0.10% or more of each of these elements. As long as each of these elements is included in a range of less than 0.25%, they do not affect the formation of Al-Si-O-based compounds, so the content of each of these elements, except for Fe, is set to less than 0.25%.

[0050] When a coating layer is produced by a hot-dip coating method, some Fe may diffuse into the coating layer as a base iron element. However, the Fe concentration range typically contained in these production methods is less than 5.0%, and this concentration range does not affect the formation of Al—Si—O-based compounds, so the Fe content is set to less than 5.0%.

[0051] Element Group D (Sb: 0% or more and 0.5% or less, Pb: 0% or more and 0.5% or less, B: 0% or more and 0.5% or less, P: 0% or more and 0.5% or less) The elements included in element group D (Sb, Pb, B, P) are semi-metallic elements that can be added to the plating layer. The inclusion of these elements has the effect of improving the corrosion resistance of the flat portion of the plating layer. Since a clear improvement in corrosion resistance has been confirmed when the content is 0.1% or more, it is preferable to include 0.1% or more of each of these elements. As long as these elements are included in the range of 0.5% or less, they do not affect the formation of Al-Si-O-based compounds, and therefore the content of each of these elements is set to 0.5% or less.

[0052] Impurities Impurities refer to components contained in raw materials or components mixed in during the manufacturing process, but not intentionally included. For example, trace amounts of components other than Fe may be mixed into the coating layer due to atomic diffusion between the steel (base steel) and the coating bath. Impurities also include oxygen. The coating layer according to this embodiment contains small amounts of impurity-level oxygen due to the contact of the molten coating layer with oxygen when removed from the coating bath during the manufacturing process. This impurity-level oxygen forms Al-Si-O-based compounds. The presence of oxygen in the coating layer can be confirmed by quantitatively analyzing the oxygen content of the cross-sectional structure of the coating layer using EPMA or the like.

[0053] 3.0≦Si / ΣA<50.0 Element group A is Mg ２ Like Si, Zn forms compounds that have a significant effect on sacrificial corrosion protection, and it easily combines with Mg, which can ultimately change the effect of Si. Therefore, it is preferable to set the ratio of the total amount of element group A (ΣA) to Si (Si / ΣA) within an appropriate range. By controlling the added amount, the effect of Si can be maximized, resulting in a plating layer with excellent performance. By setting Si / ΣA to 3.0 or more and less than 50.0, a plating layer with excellent sacrificial corrosion protection can be obtained. For example, a plating layer that is resistant to appearance changes can be created while ensuring excellent sacrificial corrosion protection at cut end surfaces and plated areas. If Si / ΣA is less than 3.0, the sacrificial corrosion protection effect may be too strong, making the appearance more susceptible to change. Furthermore, if Si / ΣA is 50.0 or more, the effect of improving sacrificial corrosion protection cannot be expected. A more preferable range of Si / ΣA is 3.0 or more. A more preferable range of Si / ΣA is 10.0 or less, and even more preferably 7.0 or less.

[0054] To identify the average chemical composition of the plating layer, the plating layer is stripped and dissolved using an acid containing an inhibitor that suppresses corrosion of the base steel (steel material) to obtain an acid solution. The resulting acid solution is then measured using ICP atomic emission spectroscopy or ICP-MS to obtain the chemical composition. There are no particular restrictions on the type of acid, as long as it is an acid that can dissolve the plating layer. By measuring the area and weight before and after stripping, the plating adhesion amount (g / m２ ) can also be obtained at the same time.

[0055] Next, we will explain the compounds that form a dense oxide film on the surface of a Zn-Al-Mg based plating layer. The main constituent element of the oxide film formed on the surface of the plating layer is Al contained in the plating layer. Al is contained in large amounts mainly in the phase mainly composed of Al (hereinafter referred to as Al phase) in the plating layer. The Al contained in this Al phase is the Al in the oxide film. ２ O ３ However, in conventional Zn-Al-Mg-based plating layers, the area ratio of the Al phase contained in the plating layer is less than about 70%, so the amount of Al necessary to sufficiently form an oxide film is insufficient, resulting in defects in the oxide film. These defects act as a starting point for corrosion of the plating layer, making the appearance of the plating layer more likely to change. On the other hand, conventional Galvalume steel sheets (registered trademark) and the like have an area ratio of the Al phase exceeding 70%, so appearance changes are less likely to occur, but sacrificial corrosion protection is low.

[0056] In this embodiment, Al-Si-O compounds are formed in the Zn-Al-Mg-based plating layer to compensate for defects in the oxide film formed on the surface of the plating layer. ２ O ３ and SiO ２ It has been found through XPS analysis that Al-Si-O compounds form a dense oxide film and can compensate for the defects of the conventional oxide film. ２ O ５ It is presumed that Si (JCPDS Card No. 01-075-4827) is formed.

[0057] It is difficult to examine the relationship between the corrosion resistance and the oxide films formed from these compounds using a TEM or the like. However, since plating layers containing Al-Si-O based compounds are less susceptible to changes in appearance, it is clear that the inclusion of Al-Si-O based compounds improves the appearance change and corrosion resistance of the plating layer.

[0058] The detection of Al-Si-O based compounds can be easily confirmed by using X-ray diffraction. That is, when diffraction peaks such as 16.18° ((110) plane) and 32.69° ((220) plane) are detected in the X-ray diffraction pattern as diffraction angles shown in JCPDS card No. 01-075-4827, it can be determined that Al-Si-O based compounds are present in the plating layer. Diffraction peaks other than these are due to Al, Mg, and Zn in the Zn-Al-Mg based plating layer. ２ There may be overlaps with other items, etc., and they are not suitable for identification.

[0059] For example, the X-ray diffraction patterns shown in Figure 1 are the results of X-ray diffraction measurements of the surfaces of coating layers containing 21% Al, 7% Mg, 0%, 0.2%, 0.4%, or 0.6% Si, with the balance being Zn and impurities. As shown in Figure 1, it can be confirmed that the X-ray diffraction peaks at 16.18° and 32.69° increase with increasing Si content, indicating that Al as an Al-Si-O compound is present. ２ O ５ The presence of Si (JCPDS card No. 01-075-4827) can be confirmed. Note that the X-ray diffraction image obtained varies depending on the X-ray irradiation conditions, so the conditions for obtaining the X-ray diffraction image are as follows.

[0060] As an X-ray source, X-rays (CuKα rays) targeting Cu are the most convenient because they can obtain average information about the constituent phases in the plating layer. Other measurement conditions include an X-ray output condition of a voltage of 40 kV and a current of 150 mA. There are no particular limitations on the X-ray diffraction device, but for example, a horizontal sample-type high-power X-ray diffraction device RINT-TTR III manufactured by Rigaku Corporation can be used.

[0061] As measurement conditions other than the X-ray source, it is preferable to use a goniometer TTR (horizontal goniometer), set the slit width of the Kβ filter to 0.05 mm, the length limiting slit to 2 mm, the light receiving slit to 8 mm, the light receiving slit 2 open, the scan speed to 5 deg. / min, the step width to 0.01 deg, and the scan axis 2θ to 5 to 90°.

[0062] For the measurement, X-rays are irradiated onto the surface of the plating layer. The measurement is performed on the plating layer as is, without sample preparation. Because diffraction intensity varies depending on the model, it is better to determine the presence or absence of diffraction peaks based on the relative intensity at a specific angle. Specifically, as illustrated in FIG. 1 , in the plating layer according to this embodiment, no diffraction peak is observed around a diffraction angle of 27.0°. Therefore, the ratio of the sum of the diffraction peak intensities (cps) at 16.18° and 32.69° to the diffraction intensity (cps) at 27.0° is used as the evaluation parameter. That is, in this embodiment, the diffraction intensity ratio R1 defined by Equation 4 must satisfy Equation 5.

[0063] Note that if a diffraction peak with an intensity of 1000 cps or more appears at 2θ = 27.0°, I(27.0°) in Equation 4 is set to 585 cps. That is, it is set as in Equation 4-1. If a diffraction peak with an intensity of 1000 cps or more appears at 2θ = 27.0°, it is an exception because some compound is contained in the plating layer, and the appropriate diffraction intensity cannot be obtained. The value of 585 cps used instead is the average value of the measurement data (actual values) of the diffraction intensity of the plating layer according to this embodiment, and corresponds to the background intensity. As described above, since no diffraction peak due to the crystalline phase contained in the plating layer is obtained at or near 2θ = 27.0°, the diffraction intensity at 2θ = 27.0° can be used as the average value of the blank and can be used as the background intensity in the diffraction intensity.

[0064] R1 = {I(16.18°) + I(32.69°)} / I(27.0°) ...Equation 4 2.5 < R1 ...Equation 5

[0065] R1 = {I(16.18°) + I(32.69°)} / 585 ... Equation 4-1

[0066] In the formulas 4 and 4-1, I(16.18°) is the diffraction intensity at 2θ=16.18° in the X-ray diffraction pattern, I(32.69°) is the diffraction intensity at 2θ=32.69° in the X-ray diffraction pattern, and I(27.0°) is the diffraction intensity at 2θ=27.0° in the X-ray diffraction pattern.

[0067] By satisfying formula 5, Al ２ O ５ It can be confirmed that Al-Si-O compounds, typified by Si, are present in the plating layer. The greater the content of Al-Si-O compounds, the denser and stronger the oxide film becomes, making it less susceptible to appearance changes and further improving corrosion resistance. These effects are enhanced as the content of Al-Si-O compounds increases, making it less susceptible to long-term appearance changes. Therefore, it is more preferable that the diffraction intensity ratio R1 is greater than 10, as shown in Equation 8. If the diffraction intensity R1 is greater than 10, the plating layer will contain sufficient Al-Si-O compounds, and long-term changes in the appearance of the plating layer can be significantly suppressed.

[0068] 10<R1...Formula 8

[0069] It is not necessary to particularly set an upper limit for the diffraction intensity ratio R1, but R1 may be 20 or less, 15 or less, or 12 or less.

[0070] In addition, the plating layer according to this embodiment contains Mg ２ Si may be contained. ２ The presence of Si can be confirmed by X-ray diffraction. ２ The diffraction intensity of Si is known to be the diffraction peaks at diffraction angles of 24.24° ((111) plane) and 28.07° ((200) plane). When X-ray diffraction measurement was performed on the plating layer surface, these diffraction peaks were detected in the X-ray diffraction pattern, indicating that Mg ２ The presence of Si can be observed. In the present embodiment, it is preferable that the diffraction intensity R2 expressed by Equation 6 satisfies Equation 7. In the plating layer according to this embodiment, since no diffraction peak is observed near a diffraction angle of 27.0°, the ratio of the sum of the diffraction peak intensity (cps) at 24.24° and the diffraction peak intensity (cps) at 28.07° to the diffraction intensity (cps) at 27.0° is used as an evaluation parameter.

[0071] When a diffraction peak with an intensity of 1000 cps or more appears at 2θ=27.0°, I(27.0°) in Equation 6 is set to 585 cps, i.e., as shown in Equation 6-1.

[0072] R2={I(24.24°)+I(28.07°)} / I(27.0°)...Formula 6 2.5<R2...Formula 7

[0073] R2 = {I(24.24°) + I(28.07°)} / 585 ...Equation 6-1

[0074] In Equation 6 and Equation 6-1, I(24.24°) is the diffraction intensity at 2θ=24.24° in the X-ray diffraction pattern, and I(28.07°) is the diffraction intensity at 2θ=28.07° in the X-ray diffraction pattern. Furthermore, I(27.0°) is the diffraction intensity at 2θ=27.0° in the X-ray diffraction pattern. The conditions for the X-ray diffraction measurement to determine the diffraction intensity ratio R2 are the same as those for determining the diffraction intensity ratio R1.

[0075] By making the diffraction intensity ratio R2 exceed 2.5, Mg is contained in the plating layer. ２ The amount of Si contained in the coating is sufficient to prevent the coating layer from turning black. ２ When Si increases and the diffraction intensity ratio R2 increases, the Al-Si-O compounds decrease, which may affect the appearance of the plating layer. ２ The ternary eutectic structure may become smaller, and the corrosion resistance of the coating layer may be reduced. Therefore, the diffraction intensity ratio R2 may be 20 or less, 15 or less, or 12 or less.

[0076] Next, a method for manufacturing a plated steel material according to this embodiment will be described. The plated steel material according to this embodiment comprises a steel material and a plating layer formed on the surface of the steel material. Typically, Zn-Al-Mg-based plating is formed by metal deposition and solidification reaction. The easiest means for forming a plating layer is to form a plating layer on the surface of a steel sheet by hot-dip plating, and this can be done by the Sendzimir method, flux method, or the like. Furthermore, the plated steel material according to this embodiment may also be formed by vapor deposition plating or a plating film formation method by thermal spraying, and the same effects as when formed by hot-dip plating can be obtained.

[0077] Hereinafter, a case where the plated steel material of this embodiment is produced by a hot-dip galvanizing method will be described. The plated steel material of this embodiment can be produced by either an immersion-type plating method (batch type) or a continuous plating method.

[0078] There are no particular restrictions on the size, shape, or surface form of the steel material to be plated. Normal steel, stainless steel, or other steel materials can be used. Steel strips of general structural steel are most preferable. Surface finishing by shot blasting or the like may be carried out in advance, and the surface may be plated with 3 g / m of Ni, Fe, Zn, or the like. ２ There is no problem if the following metal or alloy film is attached before plating. As a pre-treatment of the steel material, it is preferable to thoroughly clean the steel material by degreasing and pickling.

[0079] H ２ After the surface of the steel sheet is sufficiently heated and reduced with a reducing gas such as HCl, the steel sheet is immersed in a plating bath prepared to have the specified components.

[0080] In the case of hot-dip plating, the composition of the plating layer can be controlled by the composition of the plating bath to be prepared. The plating bath is prepared by mixing predetermined amounts of pure metals, for example, by melting in an inert atmosphere, to prepare an alloy of the plating bath components. Since the composition of the plating bath and the composition of the plating layer are nearly identical, the composition of the plating bath can be adjusted to the composition of the plating layer described above.

[0081] Immersing a steel material whose surface has been reduced in a coating bath maintained at a predetermined concentration forms a coating layer with approximately the same composition as the coating bath. If the immersion time is prolonged or if it takes a long time for solidification to be completed, the formation of the interfacial alloy layer becomes active, which may result in a high Fe concentration. However, if the temperature of the coating bath is less than 500°C, the reaction with the coating layer rapidly slows down, so the Fe concentration in the coating layer is usually less than 5.0%.

[0082] To form the hot-dip coating layer, it is preferable to immerse the reduced steel material in a coating bath at 500°C to 650°C for several seconds. On the surface of the reduced steel material, Fe diffuses into the coating bath and reacts with the coating bath, forming an interfacial alloy layer (mainly an Al-Fe-based intermetallic compound layer) at the interface between the coating layer and the steel sheet. The interfacial alloy layer metallurgically bonds the steel material below the interfacial alloy layer to the coating layer above.

[0083] After immersing the steel material in the plating bath for a predetermined time, the steel material is removed from the plating bath, and the metal adhering to the surface is in a molten state. ２ By wiping, the plating layer is adjusted to a predetermined thickness. The thickness of the plating layer is preferably adjusted to 3 to 80 μm. This corresponds to a coating weight of the plating layer of 10 to 500 g / m. ２ The thickness of the plating layer may be adjusted to 5 to 70 μm. This corresponds to a coating weight of 20 to 400 g / m. ２ (One-sided).

[0084] After adjusting the coating weight of the coating layer, the deposited molten metal is solidified. The cooling method during solidification of the coating may be performed by spraying nitrogen, air, or a hydrogen / helium mixed gas, or by mist cooling or submersion in water. Mist cooling is preferred, and mist cooling using nitrogen containing water is preferable. The cooling rate may be adjusted by adjusting the water content.

[0085] Regarding the formation of Al—Si—O, it is necessary to strictly control the oxygen concentration and temperature range after immersion in the plating bath. In the case of the plating composition according to this embodiment, it is very susceptible to bonding with oxygen, and if the oxygen concentration and cooling rate are not controlled within an appropriate temperature range, a cloudy oxide film will form on the surface of the plating layer, resulting in poor appearance, unstable formation of Al—Si—O, and the failure to obtain the desired plating layer. Therefore, in this embodiment, it is desirable to adopt the following manufacturing conditions.

[0086] The atmosphere in contact with the surface of the coating bath must not have a low oxygen concentration, and the coating bath is preferably placed in the atmosphere. Therefore, the steel material is passed through the atmosphere from the time when the steel material is immersed in the coating bath until immediately after the steel material is pulled out of the coating bath. In other words, the steel material must be in contact with the atmosphere immediately after being pulled out of the coating bath.

[0087] Cooling of the molten metal begins when the steel material is pulled out of the coating bath. In this embodiment, after the steel material is pulled out of the coating bath, it is necessary to plunge the steel material into an atmosphere with a low oxygen concentration while the temperature of the molten metal adhering to the steel material surface is in the range of 490 to 400°C. Specifically, the oxygen concentration in the atmosphere between 490 and 400°C is less than 3000 ppm. More preferably, the oxygen concentration in the atmosphere between 490 and 400°C is less than 2000 ppm, and even more preferably less than 1000 ppm. Since the molten metal on the steel material surface needs to be in contact with the air immediately after pulling out of the coating bath, the coating bath temperature needs to be maintained above 490°C, preferably 500°C or higher. The oxygen concentration in the atmosphere between the coating bath temperature and 490°C is preferably 3000 ppm or higher.

[0088] The average cooling rate between the bath temperature and 400°C is less than 15°C / sec. If the average cooling rate is 15°C / sec or more, Al-Ca-Si compounds and Mg ２ The average cooling rate to 400°C should always be less than 15°C / sec.

[0089] While the temperature of the coating layer is between 400 and 300°C, it is cooled in the atmosphere. Furthermore, cooling when the temperature of the coating layer is below 400°C is required to be rapid, and the average cooling rate between 400 and 300°C is set to 15°C / second or more. If the average cooling rate is less than 15°C / second, the Al-Si-O-based compounds formed on the surface of the coating layer will settle inside the molten coating layer, making it difficult to form an oxide film on the surface of the coating layer.

[0090] In the method for producing a plated steel material according to this embodiment, the oxygen concentration and average cooling rate are controlled as described above from immediately after the steel material is pulled out of the coating bath until 400°C, and the coating layer is cooled in the atmosphere while the temperature of the coating layer is between 400 and 300°C, thereby forming a coating layer containing Al-Si-O-based compounds on the surface of the steel material. There is no need to particularly limit the conditions in the temperature range below 300°C. In this manner, the coating layer according to this embodiment is formed.

[0091] By exposing the steel material to the atmosphere immediately after it is pulled out of the coating bath, oxygen in the atmosphere diffuses into the molten metal with a newly formed surface, forming some of an Al-Si-O oxide film, which is the metal most susceptible to oxidation, and its compounds. By subsequently creating a low-oxygen atmosphere, excessive oxidation of the molten metal is suppressed, and at the same time, the coating layer solidifies, and an oxide film derived from Al-Si-O compounds is thought to form near the surface of the coating layer. Because this is related to the diffusion phenomenon of individual elements in oxygen and molten metal, it is assumed that the manufacturing temperature range and the concentration of each element determine the behavior of the formation of this compound, based on the mobility of the elements. Furthermore, because the composition of the coating layer and the manufacturing temperature range are limited to a specified range, excessive Mg ２ It is believed that the precipitation of Si is suppressed.

[0092] After the plating layer is formed, the plating layer may be subjected to various chemical conversion treatments or painting treatments. It is also possible to utilize the uneven pattern on the plating layer surface, or to further apply a plating layer of Cr, Ni, Au, etc., and then paint it to impart a design. Furthermore, to further improve corrosion resistance, touch-up paint for repair, thermal spraying treatment, etc. may be performed on welded parts, processed parts, etc.

[0093] The plated steel material of this embodiment may have a coating formed on the plating layer. One or more coatings may be formed. Examples of the coatings that may be formed directly on the plating layer include chromate coatings, phosphate coatings, and chromate-free coatings. The chromate treatment, phosphate treatment, and chromate-free treatment that form these coatings can be performed by known methods.

[0094] Chromate treatments include electrolytic chromate treatments that form a chromate film by electrolysis, reactive chromate treatments that form a film by utilizing a reaction with the material and then wash away excess treatment solution, and paint-on chromate treatments that apply a treatment solution to the substrate and dry it without rinsing with water to form a film. Any of these treatments may be used.

[0095] Examples of electrolytic chromate treatments include electrolytic chromate treatments using chromic acid, silica sol, resins (phosphoric acid, acrylic resins, vinyl ester resins, vinyl acetate acrylic emulsions, carboxylated styrene butadiene latex, diisopropanolamine-modified epoxy resins, etc.), and hard silica.

[0096] Examples of the phosphate treatment include zinc phosphate treatment, zinc calcium phosphate treatment, and manganese phosphate treatment.

[0097] Chromate-free treatments are particularly suitable because they do not place a burden on the environment. Chromate-free treatments include electrolytic chromate-free treatments that form a chromate-free film by electrolysis, reactive chromate-free treatments that form a film by utilizing a reaction with the material and then wash away excess treatment liquid, and paint-on chromate-free treatments that apply a treatment liquid to the substrate and dry it without rinsing with water to form a film. Any of these treatments may be used.

[0098] Furthermore, one or more organic resin coatings may be provided on the coating directly on the plating layer. The organic resin is not limited to a specific type, and examples thereof include polyester resins, polyurethane resins, epoxy resins, acrylic resins, polyolefin resins, and modified versions of these resins. Here, the term "modified version" refers to a resin obtained by reacting a reactive functional group contained in the structure of these resins with another compound (such as a monomer or a crosslinking agent) containing a functional group capable of reacting with the functional group.

[0099] Such organic resins may be a mixture of one or more unmodified organic resins, or a mixture of one or more organic resins obtained by modifying at least one other organic resin in the presence of at least one organic resin. The organic resin film may also contain any coloring pigment or anti-rust pigment. Water-based organic resins obtained by dissolving or dispersing them in water may also be used.

[0100] The basic corrosion resistance of a plated steel sheet can be evaluated by evaluating the corrosion resistance of a bare flat surface using an exposure test, a salt spray test (JIS Z2371), or a combined cyclic corrosion test (CCT) including a salt spray test. To confirm sacrificial corrosion protection, one of these tests is performed on the plated steel sheet with the cut edge open, and the superiority or inferiority of sacrificial corrosion protection can be evaluated by evaluating the red rust area ratio of the edge (the smaller the ratio, the better the corrosion resistance).

[0101] Changes in plating appearance are preferably evaluated by the change in color difference after a corrosion test. For example, initial changes in appearance are expected to be due to corrosion caused by moisture, so the color difference before and after storage in a constant temperature and humidity chamber is observed. Using a color difference meter, the color is judged based on the absolute value of ΔE, the change in the L*a*b* color space. A small ΔE indicates a small color change before and after corrosion, while a large ΔE indicates a large color change before and after corrosion. When investigating long-term corrosion, it is sufficient to evaluate the color difference before and after a salt spray test and a combined cyclic corrosion test.

[0102] ΔE is L ＊ a ＊ b ＊ The chromaticity index in the color system is a ＊ and b ＊ , the lightness index is L ＊ When this is the case, it is expressed by the following formula:

[0103] ΔE ＊ ab = √((Δa ＊ ) ２ + (Δb ＊ ) ２ + (ΔL ＊ ) ２ )

[0104] Plated steel materials (plated steel sheets) shown in Tables 2A to 6B were manufactured and their performance evaluated. Pure metals were mixed to prepare each type of plating bath. After preparing the plating alloy, Fe powder was added to prevent an increase in the Fe concentration during testing. To determine the composition of the plated steel sheets, the inhibitor was dissolved, the plating layer was stripped with hydrochloric acid, and the stripped components were analyzed using ICP. A "0" in the tables indicates that the content of the element in question was below the detection limit.

[0105] A test of the plated steel sheet was carried out using a batch-type hot-dip galvanizing simulator (manufactured by Rhesca Co., Ltd.) for a 180 x 100 size hot-rolled original sheet (1.6 to 3.2 mm). A K thermocouple was attached to a part of the plated original sheet, and N ２ (H ２ After annealing at 800°C for 1 minute in a 0.5% reduction atmosphere, the surface of the plated steel sheet was fully reduced with hydrogen and immersed in the plating bath under each condition for 3 seconds. ２ The coating thickness was adjusted to 25 to 30 μm by gas wiping. After the coated steel sheets were pulled out of the coating bath, coated steel sheets were produced under various cooling conditions A to K in Table 1.

[0106]

[0107] Condition D is a comparative condition in which the oxygen concentration is low between the bath temperature and 490°C. Condition E is a comparative condition in which the oxygen concentration is low between 400 and 300°C. Condition F is a comparative condition in which the oxygen concentration is low between the bath temperature and 490°C and between 400 and 300°C. Condition G is a comparative condition in which the average cooling rate is high between the bath temperature and 400°C. Condition H is a comparative condition in which the average cooling rate is low between 400 and 300°C. Condition K is a comparative condition in which the oxygen concentration is high between 490 and 400°C. The other conditions are preferable conditions.

[0108] The plated steel sheet was cut into 20 mm square pieces and analyzed using a high-angle X-ray diffractometer (Rigaku Corporation, model RINT-TTR III) with an X-ray output of 40 kV, 150 mA, a copper target, a TTR goniometer (horizontal goniometer), a Kβ filter slit width of 0.05 mm, a longitudinal limiting slit width of 2 mm, a receiving slit width of 8 mm, and a receiving slit 2 open. Measurement conditions included a scan speed of 5 deg. / min, a step width of 0.01 deg., and a scan axis 2θ (5 to 90°). The diffraction peak intensities (cps) at each angle were then obtained. R1 and R2 were then calculated from the diffraction intensities. In the BG Adopted Value column of Tables 6A and 6B, "27°" means that the denominator in Equation 4 and Equation 6 was I (27.0°) (diffraction intensity (cps) at 2θ = 27.0°). Also, "585" means that the denominators in Equation 4 and Equation 6 are set to 585 cps.

[0109] To evaluate the corrosion resistance of the flat surface of the plated steel sheet, a 70 x 150 mm square test piece was cut out from the manufactured plated steel sheet, the end faces of the test piece were protected with an epoxy resin-based paint, and a 5% salt spray test (JIS 2371) was carried out for 120 hours to evaluate the white rust area ratio of the evaluation surface. The evaluation criteria for the white rust area ratio are as follows: "A" or higher was considered to be acceptable.

[0110] A white rust area rate of less than 5% is rated as "AAA." A white rust area rate of 5-10% is rated as "AA." A white rust area rate of 10-20% is rated as "A." A white rust area rate of 20% or more is rated as "B."

[0111] In the early stages of the corrosion process, the more corrosion-resistant the plating layer was, the less likely white rust was to occur.

[0112] For sacrificial corrosion protection, a 70 x 150 mm square test piece was cut out from the plated steel sheet, and the JASO test (M609-91) was carried out with the four end faces of the test piece left open. After 30 cycles, the red rust area ratio on the left and right side faces of the end face was evaluated. The evaluation criteria for the red rust area ratio are as follows: "A" or higher was considered a pass.

[0113] A red rust area ratio of less than 5% is rated as "AAA." A red rust area ratio of 5-10% is rated as "AA." A red rust area ratio of 10-20% is rated as "A." A red rust area ratio of 20% or more is rated as "B."

[0114] When white rust forms over the edge of a plated steel sheet due to corrosion, the occurrence of red rust is suppressed and the red rust area ratio tends to decrease.

[0115] For the corrosion appearance evaluation (short-term), square test pieces measuring 70 x 150 mm were cut from the manufactured plated steel sheets, the end faces were protected with epoxy resin-based paint, and the plated steel sheets were left in a constant temperature and humidity chamber at 90% humidity and 70°C for 24, 48, 72, and 120 hours, and the color difference before and after the test was measured. The change in appearance of the steel sheets was evaluated based on the magnitude of the change in ΔE (SCE method). The evaluation criteria were as follows: "A" or higher was considered a pass.

[0116] ΔE is L ＊ a ＊ b ＊ The chromaticity index in the color system is a ＊ and b ＊ , the lightness index is L ＊ When the above is true, it is expressed by the following formula: "A" or higher was considered to be a pass.

[0117] ΔE ＊ ab = √((Δa ＊ ) ２ + (Δb ＊ ) ２ + (ΔL ＊ ) ２ )

[0118] If ΔE<5 continued for 120 hours or more, it was rated as "S". If ΔE<5 continued for 72 hours or more, it was rated as "AAA". If ΔE<5 continued for 48 hours or more, it was rated as "AA". If ΔE<5 continued for 24 hours or more, it was rated as "A". If ΔE<5 did not continue for less than 24 hours, it was rated as "B".

[0119] For the corrosion appearance evaluation (long-term), square test pieces measuring 70 x 150 mm were cut out from the manufactured plated steel sheets, the edge surfaces were protected with epoxy resin-based paint, and the plated steel sheets were left in the JASO test for 3, 6, 9, and 15 cycles, and the color difference ΔE before and after the test was measured in areas where no white rust had developed. The change in appearance of the steel sheets was evaluated based on the magnitude of the change in ΔE (SCE method). The evaluation criteria were as follows. A rating of "A" or higher was considered a pass.

[0120] A case where ΔE<5 continued for 15 cycles or more was designated "S". A case where ΔE<5 continued for 9 cycles or more was designated "AAA". A case where ΔE<5 continued for 6 cycles or more was designated "AA". A case where ΔE<5 continued for 3 cycles or more was designated "A". A case where ΔE<5 did not continue for 3 cycles or less was designated "B".

[0121] As shown in Tables 2A to 6B, Examples 1 to 5, 11, 12, 14 to 16, 21, 22, 26 to 46, and 48 to 51 satisfy the range of the present invention, and the corrosion resistance, sacrificial corrosion protection, corrosion appearance evaluation (short term), and corrosion appearance evaluation (long term) were all good.

[0122] In Comparative Examples 6 to 10, 13, 17 to 21, and 24, the manufacturing conditions were not favorable, so the diffraction intensity ratio R1 was 2.5 or less, and none of the properties of corrosion resistance, sacrificial corrosion protection, corrosion appearance evaluation (short-term), and corrosion appearance evaluation (long-term) were satisfactory. In Comparative Example 25, (Si / ΣB) × (Mg / Si) was 375.0 or more, so the diffraction intensity ratio R1 was 2.5 or less, and none of the properties of corrosion resistance, sacrificial corrosion protection, corrosion appearance evaluation (short-term), and corrosion appearance evaluation (long-term) were satisfactory. In Comparative Example 47, (Si / ΣB) × (Mg / Si) was less than 26.0, so the diffraction intensity ratio R1 was 2.5 or less, and none of the properties of corrosion resistance, sacrificial corrosion protection, corrosion appearance evaluation (short-term), and corrosion appearance evaluation (long-term) were satisfactory. In Comparative Examples 52 to 78, the average chemical composition of the plating layer was outside the range of the present invention, resulting in a diffraction intensity ratio R1 of 2.5 or less, and none of the properties of corrosion resistance, sacrificial corrosion protection, corrosion appearance evaluation (short-term), and corrosion appearance evaluation (long-term) were satisfactory.

[0123]

[0124]

[0125]

[0126]

[0127]

[0128]

[0129]

[0130]

[0131]

[0132]

[0133] According to the present invention, it is possible to provide a Zn-based plated steel material that exhibits little change in appearance over a long period of time, and therefore the present invention has a high industrial applicability.

Claims

1. A plated steel material having a plating layer on a steel material surface, the plating layer having an average chemical composition, in mass%, of: Zn: more than 50.00%, Al: more than 15.0% and less than 30.0%, Mg: more than 5.0% and less than 15.0%, Si: 0.25% or more and less than 3.50%, Sn: 0% or more and less than 1.00%, Bi: 0% or more and less than 1.00%, In: 0% or more and less than 1.00%, Ca: 0% or more and less than 0.60%, Y: 0% or more and less than 0.60%, La: 0% or more and less than 0.60%, Ce: 0% or more and less than 0.60%, Sr: 0% or more and less than 0.60%, Cr: 0% or more and less than 0.25%, Ti: 0% or more and less than 0.25%, Ni: 0% or more and less than 0.25%, Co: 0% or more and less than 0.25%, V: 0% or more and less than 0.25%, Nb: 0% or more and less than 0.25%, Zr: 0% or more and less than 0.25%, Mo: 0% or more and less than 0.25%, W: 0% or more and less than 0.25%, Ag: 0% or more and less than 0.25%, Cu: 0% or more and less than 0.25%, Mn: 0% or more and less than 0.25%, Fe: 0% or more and less than 5.0%, Sb: 0% or more and less than 0.5%, Pb: 0% or more and less than 0.5%, B: 0% or more and less than 0.5%, P: 0% or more and less than 0.5%, and impurities, and the total amount (ΣA) of at least one selected from the group consisting of Sn, Bi and In is less than 1.00%, a plated steel material in which a total amount (ΣB) of at least one element selected from the group consisting of Ca, Y, La, Ce, and Sr is 0.02% or more and less than 0.60%, the Mg content, the Si content, and the ΣB satisfy the following formulas 1 to 3, and in an X-ray diffraction pattern of the plated layer surface, measured using Cu-Kα radiation under conditions of an X-ray output of 40 kV and 150 mA, a diffraction intensity ratio R1 defined by the following formula 4 satisfies the following formula 5.where R1 is the average composition (mass%) of Si and Mg in the plating layer, I(16.18°) is the diffraction intensity (cps) at 2θ=16.18° in the X-ray diffraction pattern, I(32.69°) is the diffraction intensity (cps) at 2θ=32.69° in the X-ray diffraction pattern, and I(27.0°) is the diffraction intensity (cps) at 2θ=27.0° in the X-ray diffraction pattern. When a diffraction peak having an intensity of 1000 cps or more appears at 2θ=27.0°, I(27.0°) in the formula 4 is set to 585 cps.

2. The plated steel product according to claim 1, wherein in an X-ray diffraction pattern of the surface of the plated layer measured using Cu-Kα radiation under conditions of an X-ray output of 40 kV and 150 mA, a diffraction intensity ratio R2 defined by the following formula 6 satisfies the following formula 7: R2={I(24.24°)+I(28.07°)} / I(27.0°) ... formula 6 2.5<R2 ... formula 7 In formula 6, I(24.24°) is the diffraction intensity (cps) at 2θ=24.24° in the X-ray diffraction pattern, I(28.07°) is the diffraction intensity (cps) at 2θ=28.07° in the X-ray diffraction pattern, and I(27.0°) is the diffraction intensity (cps) at 2θ=27.0° in the X-ray diffraction pattern. When a diffraction peak having an intensity of 1000 cps or more appears at 2θ=27.0°, I(27.0°) in the formula 6 is set to 585 cps.

3. The plated steel material according to claim 1 or 2, wherein R1 defined by formula 4 satisfies the following formula 8: 10<R1 ... formula 8 4. The plated steel material according to any one of claims 1 to 3, which satisfies the following formula 9: 3.0≦Si / ΣA<50.0 ... formula 9, where Si in formula 9 is the average composition (mass%) of Si in the plated layer.

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