Specification
Title of Invention : Galvanized steel
Technical field
[0001]
This disclosure relates to plated steel.
Background technology
[0002]
For example, in the field of building materials, a wide variety of plated steel materials are used. Most of them are Zn-plated steel. Due to the need to extend the life of building materials, research has been conducted for a long time to improve the corrosion resistance of Zn-plated steel materials, and various plated steel materials have been developed. The first high-corrosion-resistant plated steel for building materials is a Zn-5% Al-plated steel (Galfan-plated steel) in which Al is added to the Zn-based plating layer to improve corrosion resistance. It is a well-known fact that Al is added to the plating layer to improve corrosion resistance. Addition of 5% Al forms Al crystals in the plating layer (specifically, the Zn phase) to improve corrosion resistance. Zn-55% Al-1.6% Si plated steel (Galvalume steel) is basically a plated steel with improved corrosion resistance for the same reason.
Therefore, if the Al concentration is improved, the flat surface corrosion resistance is basically improved. However, an increase in Al concentration causes a decrease in sacrificial corrosion resistance.
[0003]
Here, the attraction of Zn-based plated steel is its sacrificial anti-corrosion effect on the base steel. In other words, at the cut edges of the plated steel, cracks in the plating layer during processing, and exposed portions of the base steel that appear due to peeling of the plating layer, etc., the surrounding plating layer elutes before the base steel is corroded, protecting the eluted plating components. Forms a film. This makes it possible to prevent red rust from the base steel material to some extent.
[0004]
This action is generally preferred when the Al concentration is low and the Zn concentration is high. Therefore, in recent years, highly corrosion-resistant plated steel materials in which the Al concentration is suppressed to a relatively low concentration of about 5% to 25% have been put to practical use. In particular, a plated steel material containing about 1 to 3% of Mg while keeping the Al concentration low has flat surface corrosion resistance and sacrificial corrosion resistance superior to those of Galfan plated steel material. Therefore, it became a trend in the market as a plated steel material, and is now widely known in the market.
[0005]
As a plated steel material containing certain amounts of Al and Mg, for example, the plated steel material disclosed in Patent Document 1 has also been developed.
[0006]
Specifically, in Patent Document 1, the surface of the steel material is composed of Al: 5 to 18% by mass, Mg: 1 to 10% by mass, Si: 0.01 to 2% by mass, and the balance Zn and unavoidable impurities. A hot-dip Zn--Al--Mg--Si coated steel material is disclosed in which 200 or more Al phases exist per 1 mm 2 on the surface of the coated steel material having a coating layer.
prior art documents
patent literature
[0007]
Patent Document 1: JP-A-2001-355053
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0008]
However, with plated steel containing a certain amount of Al concentration, the corrosion of the plated layer (specifically, the Zn-Al-Mg alloy layer) progresses locally, and there is a high tendency to reach the base steel at an early stage. As a result, the corrosion resistance of the flat surface deteriorates, and the variation in the corrosion resistance of the flat surface increases. Therefore, at present, there is a demand for a plated steel material having stable and high flat surface corrosion resistance.
[0009]
In addition, in order to enhance sacrificial corrosion resistance in the plating layer, it is necessary to include a structure that is easily dissolved in water (hereinafter also referred to as "water-soluble structure"). However, the water-soluble structure also dissolves in water condensed on the surface of the plated steel material from the moisture in the air. As a result, the surface of the plated steel may be discolored black from an early stage after the production of the plated steel.
[0010]
Therefore, an object of one aspect of the present disclosure is to provide a plated steel material that has high discoloration resistance while ensuring flat surface corrosion resistance and sacrificial corrosion resistance.
Means to solve problems
[0011]
The above issues will be resolved by the following means.
[0012]
<1>
A plated steel material having a base steel material and a plating layer including a Zn-Al-Mg alloy layer disposed on the surface of the base steel material,
　The plating layer, in mass%,
Zn: more than 65.0%,
Al: more than 5.0% to less than 25.0%,
Mg: more than 3.0% to less than 12.5%,
Sn: 0 to 0.20%,
Bi: 0% to less than 5.0%,
In: 0% to less than 2.0%,
Ca: 0% to 3.0%,
Y: 0% to 0.5%,
La: 0% to less than 0.5%,
Ce: 0% to less than 0.5%,
Si: 0% to less than 2.5%,
Cr: 0% to 0.25%,
Ti: 0% to 0.25%,
Ni: 0% to 0.25%,
Co: 0% to 0.25%,
　V: 0% to 0.25%,
Nb: 0% to 0.25%,
Cu: 0% to 0.25%,
Mn: 0% to 0.25%,
Fe: 0% to 5.0%,
Sr: 0% to less than 0.5%,
Sb: 0% to less than 0.5%,
Pb: 0% to less than 0.5%,
B: 0% to less than 0.5%, and
has a chemical composition consisting of impurities,
After polishing the surface of the Zn-Al-Mg alloy layer to 1/2 of the layer thickness, in the backscattered electron image of the Zn-Al-Mg alloy layer obtained when observed with a scanning electron microscope at a magnification of 100 times, A plated steel material in which Al crystals are present and the average value of the cumulative perimeter of the Al crystals is 88 to 195 mm/mm 2 .
<2>
The plated steel material according to <1>, wherein the Sn content is 0 to less than 0.10% by mass. <3>
The plated steel material according to <1> or <2>, wherein the plated layer has an Al-Fe alloy layer with a thickness of 0.05 to 5 μm between the base steel material and the Zn-Al-Mg alloy layer.
Effect of the invention
[0013]
According to one aspect of the present disclosure, it is possible to provide a plated steel material having high discoloration resistance while ensuring flat surface corrosion resistance and sacrificial corrosion resistance.
Brief description of the drawing
[0014]
FIG. 1 is a backscattered electron image of SEM (100× magnification) showing an example of a Zn—Al—Mg alloy layer of a plated steel material of the present disclosure.
2 is a SEM backscattered electron image (magnification: 500) showing an example of a Zn—Al—Mg alloy layer of the plated steel material of the present disclosure. FIG.
3 is a SEM backscattered electron image (10000× magnification) showing an example of a Zn—Al—Mg alloy layer of the plated steel material of the present disclosure. FIG.
[Fig. 4] A diagram showing an example of a backscattered electron image (backscattered electron image of SEM) of the Zn-Al-Mg alloy layer of the plated steel material of the present disclosure, which has undergone image processing (binarization) so that Al crystals can be identified. is.
MODE FOR CARRYING OUT THE INVENTION
[0015]
An example of the present disclosure will be described below.
In addition, in the present disclosure, the "%" display of the content of each element in the chemical composition means "% by mass".
A numerical range expressed using "~" means a range that includes the numerical values ​​described before and after "~" as lower and upper limits.
A numerical range when "more than" or "less than" is attached to the numerical value described before and after "~" means a range that does not include these numerical values ​​as the lower or upper limit.
The content of an element in a chemical composition is sometimes expressed as element concentration (eg, Zn concentration, Mg concentration, etc.).
The term "process" includes not only an independent process, but also if the intended purpose of the process is achieved, even if it cannot be clearly distinguished from other processes.
"Flat surface corrosion resistance" refers to the resistance to corrosion of the plating layer (specifically, the Zn-Al-Mg alloy layer) itself.
"Sacrificial corrosion resistance" refers to corrosion of the base steel at exposed parts (for example, cut edges of plated steel, cracks in the coating layer during processing, and locations where the base steel is exposed due to peeling of the coating layer). It exhibits suppressive properties.
"Discoloration resistance" refers to the property that the surface of the plated steel (that is, the surface of the plating layer) does not easily turn black after the plated steel is manufactured.
[0016]
The plated steel material of the present disclosure is a plated steel material that has a base steel material and a plating layer that is arranged on the surface of the base steel material and includes a Zn-Al-Mg alloy layer.
In the plated steel material of the present disclosure, the plating layer has a predetermined chemical composition, and after polishing the surface of the Zn-Al-Mg alloy layer to 1/2 of the layer thickness, it is observed with a scanning electron microscope at a magnification of 100 times. In a backscattered electron image of the Zn--Al--Mg alloy layer obtained by observation, Al crystals are present, and the average value of the cumulative perimeter of the Al crystals is 88 to 195 mm/mm 2 .
[0017]
Due to the above configuration, the plated steel material of the present disclosure is a plated steel material having high discoloration resistance while ensuring flat surface corrosion resistance and sacrificial corrosion resistance. The plated steel material of the present disclosure was discovered based on the following findings.
[0018]
The inventors analyzed the initial corrosion behavior of the plating layer including the Zn-Al-Mg alloy layer. As a result, it was found that the corrosion of the plating layer (specifically, the Zn--Al--Mg alloy layer) progressed locally like an ant's nest, preferentially corroding around the Al crystals.
This is estimated as follows. Potentiometric corrosion occurs between the Al crystal having a relatively high potential and the surrounding structure having a low potential. Therefore, the larger the contact area between the Al crystal and the phase around the Al crystal, the more likely corrosion occurs around the Al crystal, which deteriorates the corrosion resistance of the flat surface and increases the variation in the corrosion resistance of the flat surface.
[0019]
Therefore, in order to reduce the contact area between the Al crystal and the phase surrounding the Al crystal as much as possible, the inventors control the cooling conditions after immersion in the plating bath during the production of the plating layer to precipitate Al crystals coarsely. I came up with the idea.
As a result, we found the following. As an index of the size of Al crystals, the cumulative perimeter of Al crystals obtained by image analysis correlates well with the corrosion resistance of the plane portion. When the average value of the cumulative peripheral length of the Al crystal is within a predetermined range, the contact area between the Al crystal and the surrounding phase of the Al crystal is reduced. As a result, preferential corrosion around Al crystals is suppressed, and stable planar corrosion resistance is obtained. However, if the average value of the cumulative circumference length of the Al crystal is excessively decreased, the workability is deteriorated.
[0020]
On the other hand, the inventors studied the Sn content, which enhances sacrificial corrosion resistance, and obtained the following findings.
In order to increase the sacrificial corrosion resistance, if the plating layer contains more than 0.20% Sn, a water-soluble Mg2Sn phase is generated. However, the Mg 2 Sn phase, which is a water-soluble structure, also dissolves in water condensed on the surface of the plated steel material from moisture in the atmosphere. As a result, after the production of the plated steel, the surface of the plated steel may turn black over time.
Therefore, by suppressing the Sn content to 0 to 0.20%, excessive generation of the Mg2Sn phase, which is a water-soluble structure, can be suppressed. As a result, along with the corrosion resistance of the plane portion, the sacrificial corrosion resistance is ensured, and the discoloration resistance is enhanced.
[0021]
From the above, it was found that the plated steel material of the present disclosure is a plated steel material having high discoloration resistance while ensuring flat surface corrosion resistance and sacrificial corrosion resistance.
[0022]
Details of the plated steel material of the present disclosure will be described below.
[0023]
　The base steel material to be plated will be explained.
There are no particular restrictions on the shape of the base steel material. Base steel materials include steel plates, steel pipes, civil engineering and construction materials (fences, corrugated pipes, drain covers, sand prevention plates, bolts, wire meshes, guardrails, water stop walls, etc.), home appliance components (outdoor unit housings for air conditioners, etc.) body, etc.), automobile parts (suspension parts, etc.), and the like. Various plastic working methods such as press working, roll forming, and bending can be used for forming.
[0024]
There are no particular restrictions on the material of the base steel. Base steel materials include, for example, general steel, pre-plated steel, Al-killed steel, ultra-low-carbon steel, high-carbon steel, various high-strength steels, and some high-alloy steels (steel containing strengthening elements such as Ni and Cr), etc. Various base steel materials are applicable.
For the base steel material, there are no particular restrictions on conditions such as the manufacturing method of the base steel material and the manufacturing method of the base steel plate (hot rolling method, pickling method, cold rolling method, etc.).
As the base steel material, hot-rolled steel sheets, hot-rolled steel strips, cold-rolled steel sheets, and cold-rolled steel strips described in JIS G 3302 (2010) can also be applied.
[0025]
The base steel material may be pre-plated pre-plated steel material. A pre-plated steel material is obtained, for example, by an electrolytic treatment method or a displacement plating method. In the electrolytic treatment method, the base steel material is immersed in a sulfuric acid bath or a chloride bath containing metal ions of various pre-plating components and electrolytically treated to obtain a pre-plated steel material. In the displacement plating method, the base steel material is immersed in an aqueous solution containing metal ions of various pre-plating components, the pH of which is adjusted with sulfuric acid.A pre-plated steel material is obtained by subjecting the metal to displacement deposition.
A typical example of pre-plated steel is pre-Ni plated steel.
[0026]
Next, the plating layer will be explained.
The plating layer includes a Zn-Al-Mg alloy layer. The plating layer may include an Al--Fe alloy layer in addition to the Zn--Al--Mg alloy layer. The Al--Fe alloy layer is provided between the base steel material and the Zn--Al--Mg alloy layer.
[0027]
That is, the plating layer may have a single layer structure of a Zn-Al-Mg alloy layer, or may have 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 a layer forming the surface of the plating layer.
However, although an oxide film of the constituent elements of the plating layer is formed on the surface of the plating layer by about 50 nm, it is considered that the thickness is thin compared to the thickness of the entire plating layer and does not constitute the main body of the plating layer.
[0028]
Here, the thickness of the Zn-Al-Mg alloy layer is, for example, 2 μm or more and 95 μm or less (preferably 5 μm or more and 75 μm or less).
[0029]
On the other hand, the thickness of the entire plating layer is, for example, about 100 μm or less. Since the thickness of the entire plating layer depends on the plating conditions, the upper and lower limits of the thickness of the entire plating layer are not particularly limited. For example, the thickness of the entire plating layer is related to the viscosity and specific gravity of the plating bath in a normal hot-dip plating method. Furthermore, the coating weight is adjusted according to the drawing speed of the base steel and the intensity of wiping. Therefore, it may be considered that the lower limit of the thickness of the entire plating layer is about 2 μm.
On the other hand, due to the weight and uniformity of the plating metal, the upper limit of the thickness of the plating layer that can be produced by the hot dip plating method is about 95 μm.
　The thickness of the plating layer can be changed freely depending on the withdrawal speed from the plating bath and the wiping conditions, so it is not particularly difficult to form a plating layer with a thickness of 2 to 95 μm.
[0030]
The amount of the plating layer attached is preferably 20 to 300 g/m2 per side.
When the coating weight of the plating layer is 20 g/m 2 or more, it is possible to more reliably secure the corrosion resistance of the flat surface and the sacrificial corrosion resistance. On the other hand, when the coating amount of the plating layer is 300 g/m 2 or less, it is possible to suppress appearance defects such as drip patterns of the plating layer.
[0031]
Next, the Al--Fe alloy layer will be explained.
[0032]
The Al--Fe alloy layer is formed on the surface of the base steel material (specifically, between the base steel material and the Zn--Al--Mg alloy layer), and the Al 5Fe phase is the main phase layer as the structure. The Al--Fe alloy layer is formed by mutual atomic diffusion of the base steel material and the plating bath. When hot-dip plating is used as a manufacturing method, an Al—Fe alloy layer is likely to be formed in a plating layer containing Al element. Since the plating bath contains Al at a certain concentration or higher, the Al 5Fe phase forms the most. However, atomic diffusion takes a long time, and there is a portion where the Fe concentration is high near the base steel material. Therefore, the Al—Fe alloy layer may partially contain a small amount of an AlFe phase, an Al 3Fe phase, an Al 5Fe 2 phase, or the like. Also, since the plating bath contains Zn at a certain concentration, the Al—Fe alloy layer also contains a small amount of Zn.
[0033]
In terms of corrosion resistance, there is no great difference between the Al 5Fe phase, Al 3Fe phase, AlFe phase, and Al 5Fe 2 phase. The corrosion resistance referred to here is the corrosion resistance of portions not affected by welding.
[0034]
Here, when Si is contained in the plating layer, Si is particularly likely to be incorporated into the Al--Fe alloy layer, and may form an Al--Fe--Si intermetallic compound phase. The identified intermetallic compound phase includes the AlFeSi phase, and α, β, q1, q2-AlFeSi phases and the like exist as isomers. Therefore, these AlFeSi phases and the like may be detected in the Al--Fe alloy layer. The Al--Fe alloy layer containing these AlFeSi phases is also called an Al--Fe--Si alloy layer.
Since the Al--Fe--Si alloy layer is also thinner than the Zn--Al--Mg alloy layer, its influence on the corrosion resistance of the entire plating layer is small.
[0035]
Also, when various pre-plated steel materials are used for the base steel material (base steel plate, etc.), the structure of the Al-Fe alloy layer may change depending on the amount of pre-plating applied. Specifically, when the pure metal layer used for pre-plating remains around the Al-Fe alloy layer, an intermetallic compound phase (for example, Al 3Ni phase, etc.) forms an alloy layer, forms an Al—Fe alloy layer in which some of the Al atoms and Fe atoms are substituted, or forms an Al atom, a portion of the Fe atoms and the Si atoms is substituted by Al -Fe--Si alloy layer may be formed. In any case, since these alloy layers are also thinner than the Zn--Al--Mg alloy layer, they have little influence on the corrosion resistance of the entire plating layer.
[0036]
In other words, the Al--Fe alloy layer is a layer that includes alloy layers of the above-described various modes in addition to the alloy layer mainly composed of the Al 5Fe phase.
[0037]
When a plating layer is formed on a pre-Ni-plated steel material among various pre-plated steel materials, an Al-Ni-Fe alloy layer is formed as the Al-Fe alloy layer. Since the Al--Ni--Fe alloy layer is also thinner than the Zn--Al--Mg alloy layer, its influence on the corrosion resistance of the entire plating layer is small.
[0038]
The thickness of the Al--Fe alloy layer is, for example, 0 μm or more and 5 μm or less.
In other words, the Al--Fe alloy layer does not have to be formed. The thickness of the Al—Fe alloy layer is preferably 0.05 μm or more and 5 μm or less from the viewpoint of enhancing the adhesion of the plating layer (specifically, the Zn—Al—Mg alloy layer) and ensuring workability.
[0039]
However, usually, when a plating layer having a chemical composition specified in the present disclosure is formed by a hot dip plating method, an Al--Fe alloy layer of 100 nm or more may be formed between the base steel material and the Zn--Al--Mg alloy layer. many. The lower limit of the thickness of the Al--Fe alloy layer is not particularly limited, and it has been found that an Al--Fe alloy layer is inevitably formed when forming a hot-dip plating layer containing Al. . Empirically, around 100 nm is the thickness at which the formation of the Al--Fe alloy layer is most suppressed, and is judged to be the thickness that sufficiently secures the adhesion between the plating layer and the base steel material. Since the Al concentration is high unless special measures are taken, it is difficult to form an Al--Fe alloy layer thinner than 100 nm by hot-dip plating. However, even if the thickness of the Al--Fe alloy layer is less than 100 nm, and even if the Al--Fe alloy layer is not formed, it is assumed that the plating performance is not significantly affected.
[0040]
On the other hand, when the thickness of the Al--Fe alloy layer exceeds 5 μm, the Al component of the Zn--Al--Mg alloy layer formed on the Al--Fe alloy layer becomes insufficient, and furthermore, the adhesion and workability of the plating layer deteriorate. tends to get worse. Therefore, it is preferable to limit the thickness of the Al--Fe alloy layer to 5 μm or less.
The Al--Fe alloy layer also has a close relationship with respect to the Al concentration and the Sn concentration, and generally the higher the Al concentration and the Sn concentration, the faster the growth rate tends to be.
[0041]
Since the Al-Fe alloy layer is often composed mainly of the Al 5Fe phase, the chemical composition of the Al-Fe alloy layer is Fe: 25 to 35%, Al: 65 to 75%, Zn: 5% or less, and Balance: A composition containing impurities can be exemplified.
[0042]
Since the thickness of the Zn-Al-Mg alloy layer is usually thicker than that of the Al-Fe alloy layer, the contribution of the Al-Fe alloy layer to the flat surface corrosion resistance as a plated steel material is Smaller than the Al—Mg alloy layer. However, the Al—Fe alloy layer contains Al and Zn, which are corrosion-resistant elements, at a certain concentration or more, as presumed from the results of component analysis. Therefore, the Al—Fe alloy layer has a certain degree of sacrificial anti-corrosion ability and corrosion barrier effect on the base steel material.
[0043]
Here, it is difficult to confirm the contribution of the thin Al-Fe alloy layer alone to corrosion resistance by quantitative measurement. However, for example, if the Al-Fe alloy layer has a sufficient thickness, the Zn-Al-Mg alloy layer on the Al-Fe alloy layer is precisely removed by cutting from the surface of the plating layer with an end mill or the like, and the corrosion test is performed. It is possible to evaluate the corrosion resistance of the Al--Fe alloy layer alone by multiplying by . Since the Al--Fe alloy layer contains an Al component and a small amount of Zn component, when the Al--Fe alloy layer is present, red rust occurs in dots, and the base steel material is exposed without the Al--Fe alloy layer. It does not become red rust all over like time.
[0044]
Also, during the corrosion test, when observing the cross-section of the plating layer just before the occurrence of red rust on the base steel material, even if the upper Zn-Al-Mg alloy layer was eluted and rusted, only the Al-Fe alloy layer remained. , it can be confirmed that the base steel is protected from corrosion. This is because the Al--Fe alloy layer is electrochemically more noble than the Zn--Al--Mg layer, but is positioned lower than the base steel material. From these facts, it can be judged that the Al--Fe alloy layer also has a certain degree of corrosion resistance.
[0045]
From the viewpoint of corrosion, the thicker the Al-Fe alloy layer, the better, and it has the effect of delaying the red rust generation time. However, since a thick Al--Fe alloy layer significantly deteriorates the plating workability, the thickness is preferably a certain thickness or less. From the standpoint of workability, the thickness of the Al—Fe alloy layer is preferably 5 μm or less. When the thickness of the Al--Fe alloy layer is 5 μm or less, the amount of cracks and powdering generated starting from the plated Al--Fe alloy layer by a V-bending test or the like is reduced. The thickness of the Al—Fe alloy layer is more preferably 2 μm or less.
[0046]
Next, the chemical composition of the plating layer will be explained.
The component composition of the Zn-Al-Mg alloy layer contained in the plating layer is almost maintained even in the Zn-Al-Mg alloy layer of the plating bath. In the hot-dip plating method, the formation of the Al--Fe alloy layer has completed the reaction in the plating bath. Very little.
[0047]
And, in order to achieve stable flat surface corrosion resistance, the chemical composition of the plating layer is as follows.
[0048]
　In other words, the chemical composition of the plating layer is, in mass%,
Zn: more than 65.0%,
Al: more than 5.0% to less than 25.0%,
Mg: more than 3.0% to less than 12.5%,
Sn: 0 to 0.20%,
Bi: 0% to less than 5.0%,
In: 0% to less than 2.0%,
Ca: 0% to 3.0%,
Y: 0% to 0.5%,
La: 0% to less than 0.5%,
Ce: 0% to less than 0.5%,
Si: 0% to less than 2.5%,
Cr: 0% to 0.25%,
Ti: 0% to 0.25%,
Ni: 0% to 0.25%,
Co: 0% to 0.25%,
　V: 0% to 0.25%,
Nb: 0% to 0.25%,
Cu: 0% to 0.25%,
Mn: 0% to 0.25%,
Fe: 0% to 5.0%,
Sr: 0% to less than 0.5%,
Sb: 0% to less than 0.5%,
Pb: 0% to less than 0.5%,
B: 0% to less than 0.5%, and
A chemical composition consisting of impurities.
[0049]
In the chemical composition of the plating layer, Bi, In, Ca, Y, La, Ce, Si, Cr, Ti, Ni, Co, V, Nb, Cu, Mn, Fe, Sr, Sb, Pb, and B are optional. is an ingredient. In other words, these elements do not have to be contained in the plating layer. When these optional components are included, the content of each optional element is preferably within the range described later.
[0050]
Here, the chemical composition of this plating layer is the average chemical composition of the entire plating layer (if the plating layer has a single-layer structure of a Zn-Al-Mg alloy layer, the average chemical composition of the Zn-Al-Mg alloy layer, the plating layer is the average chemical composition of the total of the Al--Fe alloy layer and the Zn--Al--Mg alloy layer in the case of the laminated structure of the Al--Fe alloy layer and the Zn--Al--Mg alloy layer.
[0051]
　Usually, in the hot-dip plating method,The chemical composition of the Zn--Al--Mg alloy layer is almost the same as the chemical composition of the plating bath, since the forming reaction of the plating layer is completed in the plating bath in most cases. Further, in the hot-dip plating method, the Al—Fe alloy layer is instantly formed and grown immediately after immersion in the plating bath. The Al--Fe alloy layer has completed its formation reaction in the plating bath, and its thickness is often sufficiently smaller than that of the Zn--Al--Mg alloy layer.
Therefore, unless a special heat treatment such as heat alloying treatment is performed after plating, the average chemical composition of the entire plating layer is substantially the same as the chemical composition of the Zn--Al--Mg alloy layer, and that of the Al--Fe alloy layer. component can be ignored.
[0052]
Each element of the plating layer will be described below.
[0053]

Zn is an element necessary to obtain sacrificial corrosion resistance in addition to flat surface corrosion resistance. When the Zn concentration is considered in terms of atomic composition ratio, the plating layer is composed of elements with low specific gravity such as Al and Mg.
Therefore, the Zn concentration should be over 65.0%. Zn concentration is preferably 70% or more. Note that the upper limit of the Zn concentration is the concentration of elements other than Zn and the remainder other than impurities.
[0054]

Al is an essential element for forming Al crystals and ensuring both flat surface corrosion resistance and sacrificial corrosion resistance. Al is also an essential element for enhancing the adhesion of the plating layer and ensuring workability. Therefore, the lower limit of Al concentration is more than 5.0% (preferably 10.0% or more).
above).
On the other hand, when the Al concentration increases, the sacrificial corrosion resistance tends to deteriorate. Therefore, the upper limit of Al concentration is less than 25.0% (preferably 23.0% or less).
[0055]

　Mg is an essential element for ensuring both flat surface corrosion resistance and sacrificial corrosion resistance. Therefore, the lower limit of the Mg concentration should be over 3.0% (preferably over 5.0%).
On the other hand, when the Mg concentration increases, workability tends to deteriorate. Therefore, the upper limit of the Mg concentration is less than 12.5% ​​(preferably 10.0% or less).
[0056]

Sn is an element that forms the Mg2Sn phase, which is a water-soluble structure, and imparts high sacrificial corrosion resistance. However, if Sn is contained excessively, a large amount of Mg2Sn phase, which is a water-soluble structure, is generated, resulting in deterioration of discoloration resistance. However, from the viewpoint of enhancing the sacrificial corrosion resistance, a certain amount of Sn is preferably included. Therefore, the upper limit of the Sn concentration is 0.20% or less (preferably less than 0.10%). The upper limit of the Sn concentration may be 0.09% or less, 0.08% or less, 0.07% or less, 0.06% or less, or 0.05% or less.
On the other hand, it is preferable not to contain Sn from the viewpoint of enhancing discoloration resistance. Therefore, the lower limit of Sn concentration is set to 0%. However, from the viewpoint of enhancing the sacrificial corrosion resistance, the lower limit of the Sn concentration may be more than 0%, 0.01% or more, 0.02%, or 0.03% or more.
[0057]

Bi is an element that contributes to sacrificial corrosion resistance. Therefore, the lower limit of the Bi concentration is preferably over 0% (preferably 0.1% or more, more preferably 3.0% or more).
On the other hand, when the Bi concentration increases, the flat surface corrosion resistance tends to deteriorate. Therefore, the upper limit of the Bi concentration is less than 5.0% (preferably 4.8% or less).
[0058]

In is an element that contributes to sacrificial corrosion resistance. Therefore, the lower limit of the In concentration is preferably over 0% (preferably 0.1% or more, more preferably 1.0% or more).
On the other hand, when the In concentration increases, the flat surface corrosion resistance tends to deteriorate. Therefore, the upper limit of the In concentration is less than 2.0% (preferably 1.8% or less).
[0059]

Ca is an element that can adjust the optimum amount of Mg elution to impart flat surface corrosion resistance and sacrificial corrosion resistance. Therefore, the lower limit of Ca concentration is preferably over 0% (preferably 0.05% or more).
On the other hand, when the Ca concentration increases, the flat surface corrosion resistance and workability tend to deteriorate. Therefore, the upper limit of Ca concentration is 3.0% or less (preferably 1.0% or less).
[0060]

Y is an element that contributes to sacrificial corrosion resistance. Therefore, the lower limit of the Y concentration is preferably over 0% (preferably 0.1% or more).
On the other hand, when the Y concentration increases, the flat surface corrosion resistance tends to deteriorate. Therefore, the upper limit of the Y concentration is 0.5% or less (preferably 0.3% or less).
[0061]

La and Ce are elements that contribute to sacrificial corrosion resistance. Therefore, the lower limits of La concentration and Ce concentration are preferably over 0% (preferably 0.1% or more).
On the other hand, when the La concentration and Ce concentration increase, the flat surface corrosion resistance tends to deteriorate. Therefore, the upper limits of La concentration and Ce concentration are each less than 0.5% (preferably 0.4% or less).
[0062]

　Si is an element that suppresses the growth of the Al-Fe alloy layer and contributes to the improvement of corrosion resistance. Therefore, the Si concentration is preferably over 0% (preferably 0.05% or more, more preferably 0.1% or more). In particular, when Sn is not contained (that is, when the Sn concentration is 0%), the Si concentration is preferably 0.1% or more (preferably 0.2% or more) from the viewpoint of ensuring sacrificial corrosion resistance.
On the other hand, when the Si concentration increases, the flat surface corrosion resistance, sacrificial corrosion resistance, and workability tend to deteriorate. Therefore, the upper limit of Si concentration is set to less than 2.5%. In particular, from the viewpoint of flat portion corrosion resistance and sacrificial corrosion resistance, the Si concentration is preferably 2.4% or less, more preferably 1.8% or less, and even more preferably 1.2% or less.
[0063]

Cr, Ti, Ni, Co, V, Nb, Cu and Mn are elements that contribute to sacrificial corrosion resistance. Therefore, the lower limits of the concentrations of Cr, Ti, Ni, Co, V, Nb, Cu and Mn are each preferably over 0% (preferably 0.05% or more, more preferably 0.1% or more).
On the other hand, when the concentrations of Cr, Ti, Ni, Co, V, Nb, Cu and Mn increase, the corrosion resistance of the flat surface tends to deteriorate. Therefore, the upper limits of the concentrations of Cr, Ti, Ni, Co, V, Nb, Cu and Mn are each set to 0.25% or less. The upper limit of the concentration of Cr, Ti, Ni, Co, V, Nb, Cu and Mn is preferably 0.22% or less.
[0064]

When the plating layer is formed by the hot dip plating method, the Zn-Al-Mg alloy layer and the Al-Fe alloy layer contain a certain concentration of Fe.
It has been confirmed that up to a Fe concentration of 5.0% does not adversely affect the performance even if it is included in the plating layer (especially the Zn-Al-Mg alloy layer). Since most of Fe is often contained in the Al—Fe alloy layer, the Fe concentration generally increases as the thickness of this layer increases.
[0065]

Sr, Sb, Pb and B are elements that contribute to sacrificial corrosion resistance. Therefore, it is preferable that the lower limits of the concentrations of Sr, Sb, Pb and B each exceed 0% (preferably 0.05% or more, more preferably 0.1% or more).
On the other hand, when the concentration of Sr, Sb, Pb and B increases, the corrosion resistance of the plane portion tends to deteriorate. Therefore, the upper limits of the concentrations of Sr, Sb, Pb and B are each less than 0.5%.
[0066]

Impurities refer to ingredients contained in raw materials or ingredients that are mixed in during the manufacturing process and are not intentionally included. For example, the plating layer may contain a small amount of components other than Fe as impurities due to mutual atomic diffusion between the base steel material and the plating bath.
[0067]
　The chemical composition of the plating layer is measured by the following method.
First, an acid solution is obtained by stripping and dissolving the plating layer with an acid containing an inhibitor that suppresses the corrosion of the base steel material. Next, by measuring the obtained acid solution by ICP analysis, the chemical composition of the plating layer (if the plating layer has a single-layer structure of a Zn-Al-Mg alloy layer, the chemical composition of the Zn-Al-Mg alloy layer , the total chemical composition of the Al--Fe alloy layer and the Zn--Al--Mg alloy layer) can be obtained when the plating layer has a laminated structure of an Al--Fe alloy layer and a Zn--Al--Mg alloy layer. The acid species is not particularly limited as long as it is an acid capable of dissolving the plating layer. The chemical composition is measured as an average chemical composition. Note that the Zn concentration is determined by the ICP analysis using the formula: Zn concentration=100%-concentration of other elements (%).
Here, when a pre-plated steel material is used as the base steel material, the components of the pre-plated material are also detected.
For example, when pre-Ni plated steel is used, ICP analysis detects not only Ni in the plating layer but also Ni in the pre-Ni plating. Specifically, for example, when a pre-plated steel material with a Ni adhesion amount of 1 g/m 2 to 3 g/m 2 is used as the base steel material, even if the Ni concentration contained in the plating layer is 0%, the Ni concentration is detected as 0.1-15%. On the other hand, when a pre-Ni-plated steel material is used as the base steel material, when the base steel material is immersed in the plating bath, a small amount of Ni in the pre-Ni-plated layer dissolves in the plating bath. Therefore, the Ni concentration in the plating bath is 0.02 to 0.03% higher than the Ni concentration in the freshly prepared plating bath. Therefore, when the pre-Ni plated steel material is used, the Ni concentration in the plated layer increases by 0.03% at maximum.
Therefore, in the present disclosure, when a pre-Ni-plated steel material is used, ICP analysis shows that the Ni concentration exceeds 0.28 (0.25% (upper limit of Ni concentration in the plating layer) + 0.03%)%)%. % or less, the Ni concentration in the plating layer is regarded as 0%. The Zn concentration at this time is obtained by the formula: Zn concentration=100%-concentration of elements other than Ni (%).
On the other hand, when pre-Ni-plated steel is used, when the Ni concentration exceeds 15% by ICP analysis, the plating layer contains 0.25% Ni (the upper limit of the Ni concentration in the plating layer ) is considered to be included in the above. In the present disclosure, the components of the plating layer were measured using only the ICP analysis method. can be analyzed.
[0068]
Next, the metal structure of the Zn-Al-Mg alloy layer will be explained.
[0069]
　In the metal structure of the Zn-Al-Mg alloy layer, Al crystals are present, and the average value of the total perimeter of the Al crystals is 88 to 195 mm/mm2.
[0070]
If the average value of the total perimeter of the Al crystals is less than 88 mm/mm2, the Al crystals will become too coarse and workability will deteriorate.
On the other hand, if the average value of the cumulative perimeter of the Al crystal is more than 195 mm/mm 2 , the Al crystal becomes finer and the contact area between the Al crystal and the phase surrounding the Al crystal increases. As a result, the larger the contact area between the Al crystal and the phase around the Al crystal, the more easily corrosion occurs around the Al crystal, which deteriorates the corrosion resistance of the flat surface and increases the variation in the corrosion resistance of the flat surface.
Therefore, the average value of the total perimeter of the Al crystal is 88-195mm/mm2. The lower limit of the average value of the total perimeter of the Al crystal is preferably 95 mm/mm 2 or more, more preferably 105 mm/mm 2 or more. The upper limit of the average value of the total peripheral length of the Al crystal is preferably 185 mm/mm 2 or less, more preferably 170 mm/mm 2 or less.
[0071]
The metal structure of the Zn-Al-Mg alloy layer has Al crystals. The metallographic structure of the Zn--Al--Mg alloy layer may have a Zn--Al phase in addition to the Al crystal.
[0072]
Al crystal corresponds to "the α phase that dissolves 0 to 3% of Zn". On the other hand, the Zn--Al phase corresponds to "a β phase containing more than 70% to 85% of a Zn phase (η phase) and finely separated into an α phase and a Zn phase (η phase)".[0073]
Here, FIGS. 1 to 3 show examples of SEM backscattered electron images of the Zn-Al-Mg alloy layer on the polished surface obtained by polishing the surface of the Zn-Al-Mg alloy layer to 1/2 of the layer thickness. 1 is a 100-fold magnification, FIG. 2 is a 500-fold magnification, and FIG. 3 is a backscattered electron image of a 10,000-fold SEM.
　In FIGS. 1 to 3, Al indicates an Al crystal, Zn—Al indicates a Zn—Al phase, MgZn 2 indicates a MgZn 2 phase, and Zn—Eu indicates a Zn-based eutectic phase.
[0074]
In the backscattered electron image of the Zn-Al-Mg alloy layer, the area fraction of each structure is not particularly limited, but the area fraction of the Al crystal is preferably 8 to 45% from the viewpoint of stable improvement of the corrosion resistance of the flat surface. , 15 to 35% is more preferred. In other words, it is preferable that the Al crystal exists within the above area fraction range.
[0075]
The residual structure other than the Al crystal and the Zn-Al phase includes MgZn 2 phase, Zn-based eutectic phase (specifically, Zn-Al-MgZn 2-Mg 2Sn, etc.).
[0076]
Here, the method for measuring the average value of the cumulative peripheral length of Al crystals and the area fraction of Al crystals will be described.
[0077]
The average value of the cumulative peripheral length of Al crystals and the area fraction of Al crystals were obtained by polishing the surface of the Zn-Al-Mg alloy layer to 1/2 of the layer thickness, and then using a scanning electron microscope at a magnification of 100. It is measured using a backscattered electron image of the Zn--Al--Mg alloy layer obtained when observed. Specifically, it is as follows.
[0078]
First, a sample is taken from the plated steel material to be measured. However, the sample is taken from a place where there is no defect in the plating layer, other than near the punched end face of the plated steel material (2 mm from the end face).
[0079]
Next, the surface of the plated layer (specifically, the Zn-Al-Mg alloy layer) of the sample is polished in the thickness direction of the plated layer (hereinafter also referred to as "Z-axis direction").
　The surface of the plating layer is polished in the Z-axis direction by polishing the surface of the Zn-Al-Mg alloy layer to 1/2 of the layer thickness. For this polishing, the surface of the Zn-Al-Mg alloy layer is dry-polished with a #1200-grit polishing sheet, followed by a finishing liquid containing alumina having an average particle size of 3 μm, a finishing liquid containing alumina having an average particle size of 1 μm, and colloidal polishing. Final polishing is performed using each of the finishing liquids containing silica in this order.
Before and after polishing, the Zn intensity on the surface of the Zn-Al-Mg alloy layer was measured by XRF (X-ray fluorescence analysis), and the time when the Zn intensity after polishing was 1/2 of the Zn intensity before polishing was determined. , 1/2 of the layer thickness of the Zn--Al--Mg alloy layer.
[0080]
Next, the polished surface of the Zn-Al-Mg alloy layer of the sample was observed with a scanning electron microscope (SEM) at a magnification of 100 times, and a backscattered electron image of the Zn-Al-Mg alloy layer (hereinafter "SEM backscattered electron image ) is obtained. The SEM observation conditions are acceleration voltage: 15 kV, irradiation current: 10 nA, and field size: 1222.2 μm×927.8 μm.
[0081]
　In order to identify each phase in the Zn-Al-Mg alloy layer, an FE-SEM or a TEM (transmission electron microscope) equipped with an EDS (energy dispersive X-ray spectrometer) is used. When using a TEM, FIB (focused ion beam) processing is applied to the polished surface of the Zn--Al--Mg alloy layer of the same sample to be measured. After FIB processing, a TEM electron diffraction image of the polished surface of the Zn--Al--Mg alloy layer is obtained. Then, the metal contained in the Zn--Al--Mg alloy layer is identified.
[0082]
Next, the backscattered electron image of SEM and the identification result of the electron diffraction image of FE-SEM or TEM are compared, and each phase in the Zn-Al-Mg alloy layer is identified in the backscattered electron image of SEM. In identifying each phase in the Zn--Al--Mg alloy layer, it is preferable to perform EDS point analysis and compare the result of the EDS point analysis with the identification result of the TEM electron diffraction image. An EPMA device may be used for identification of each phase.
[0083]
Next, in the backscattered electron image of the SEM, the three values ​​of grayscale brightness, hue, and contrast value indicated by each phase in the Zn-Al-Mg alloy layer are determined. Since the three values ​​of brightness, hue and contrast value shown by each phase reflect the atomic number of the element contained in each phase, usually the lower the atomic number of the Al content and the higher the Mg content, the blacker the phase. , and the higher the Zn content, the more white it tends to appear.
[0084]
From the EDS collation result, image processing (binarization ) is performed (for example, only a specific phase is displayed as a white image, and the area (number of pixels) of each phase in the field of view is calculated. See FIG. 4). By performing this image processing, the area fraction of Al crystals in the Zn--Al--Mg alloy layer occupying the backscattered electron image of the SEM is obtained.
Note that FIG. 4 is an example of an image processed (binarized) so that the Al crystal can be identified from the backscattered electron image (SEM backscattered electron image) of the Zn-Al-Mg alloy layer. Al in FIG. 4 indicates an Al crystal.
[0085]
The area fraction of Al crystals in the Zn-Al-Mg alloy layer is the average value of the area fractions of Al crystals obtained by the above operation in the three fields of view.
If it is difficult to distinguish Al crystals, electron beam diffraction or EDS point analysis by TEM is performed.
[0086]
As an example, using the binary processing function with two thresholds of WinROOF2015 (image analysis software) manufactured by Mitani Corporation, the Al crystal in the SEM backscattered electron image (grayscale image saved in 8 bits, 256 colors display) Describe the method of identification. In a grayscale image saved in 8 bits, black is represented when the luminous intensity is 0, and white is represented when the maximum value is 255. In the case of the above-described SEM backscattered electron image, it has been found from the identification results by FE-SEM and TEM that Al crystals can be identified with high accuracy when 10 and 95 are set as the light intensity thresholds. Therefore, the image is processed so that the color of these light intensity ranges from 10 to 95 changes, and the Al crystal is identified. Image analysis software other than WinROOF2015 may be used for binarization processing.
[0087]
Next, using the automatic shape feature measurement function of Mitani Shoji's WinROOF2015 (image analysis software), the perimeter lengths of the Al crystals identified by the above image processing are accumulated, and the total perimeter length of the Al crystals is obtained. Then, the total perimeter of Al crystal per unit area (mm 2 ) is calculated by dividing the total perimeter of Al crystal by the area of ​​the field of view.
This operation is performed in 3 fields of view, and the arithmetic mean of the cumulative perimeter of the Al crystal per unit area (mm 2 ) is taken as the "average value of the cumulative perimeter of the Al crystal".
[0088]
In addition, the area fraction of Al crystals can also be determined using the automatic shape feature measurement function of WinROOF2015 (image analysis software) manufactured by Mitani Corporation. Specifically, in the backscattered electron image of the Zn--Al--Mg alloy layer, the area fraction (area fraction with respect to the visual field area) of the Al crystal identified by binarization is calculated using this function. Then, this operation is performed in three fields of view, and the arithmetic average is taken as the area fraction of the Al crystal.
[0089]
　The thickness of the Al-Fe alloy layer is measured as follows.
After embedding the sample in the resin, it was polished and the backscattered electron image of the SEM of the cross section of the plating layer (cut surface along the thickness direction of the plating layer) (magnification: 5000 times, size of field: 50 μm × 200 μm, The field of view in which the Al--Fe alloy layer is visible), the thickness is measured at any five points of the identified Al--Fe alloy layer. The thickness of the Al--Fe alloy layer is taken as the arithmetic average of the five points.
[0090]
Next, an example of the method for manufacturing the plated steel material of the present disclosure will be described.
[0091]
The plated steel material of the present disclosure is obtained by forming a plating layer having the above-described predetermined chemical composition and metallographic structure on the surface (that is, one side or both sides) of the base steel material (base steel plate, etc.) by hot dip plating.
[0092]
Specifically, as an example, hot-dip plating is performed under the following conditions.
First, the plating bath temperature is set to the melting point of the plating bath +20°C or higher, and after the base steel material is pulled up from the plating bath, the temperature range from the plating bath temperature to the plating solidification start temperature is changed from the plating solidification start temperature to the plating solidification start temperature -30°C. Cool at an average cooling rate that is greater than the average cooling rate in the temperature range up to.
Next, the temperature range from the plating solidification start temperature to the plating solidification start temperature -30°C is cooled at an average cooling rate of 12°C/s or less.
Next, the temperature range from the plating solidification start temperature of -30°C to the plating solidification start temperature of -300°C is set to a higher average cooling rate than the average cooling rate of the temperature range from the plating solidification start temperature to the plating solidification start temperature of -30°C. Cool with
[0093]
That is, in one example of the method for producing a plated steel material of the present disclosure, the temperature of the plating bath is set to the melting point of the plating bath +20°C or higher, and after the base steel material is pulled up from the plating bath, the temperature range from the plating bath temperature to the plating solidification start temperature is averaged. A is the cooling rate, B is the average cooling rate in the temperature range from the plating solidification start temperature to the plating solidification start temperature -30°C, and C is the average cooling rate from the plating solidification start temperature -30°C to the plating solidification start temperature -300°C. , under the three-stage cooling conditions of A>B, B≦12° C./s, and C>B, hot-dip plating is performed on the base steel material.
[0094]
Al crystals are generated by setting the plating bath temperature to the melting point of the plating bath + 20 ° C or higher and pulling up the base steel material from the plating bath.
Then, by cooling the temperature range from the plating solidification start temperature to the plating solidification start temperature -30 ° C. at an average cooling rate of 12 ° C./s or less, Al crystals are present in the Zn-Al-Mg alloy layer. A metal structure is formed in which the average value of the cumulative perimeter of is within the above range. Cooling at this average cooling rate is carried out, for example, by air cooling in which air is blown with a weak wind.
However, from the viewpoint of preventing the plating from winding around the top roll, etc., the lower limit of the average cooling rate in the temperature range from the plating solidification start temperature to the plating solidification start temperature -30°C shall be 0.5°C/s or more.
[0095]
The plating solidification start temperature can be measured by the following method. A sample is collected from the plating bath, heated by DSC to the melting point of the plating bath +20°C or higher, and then cooled at 10°C/min.
[0096]
In the method for producing a plated steel material of the present disclosure, the average cooling rate in the temperature range from the temperature when the base steel material is pulled up from the plating bath (that is, the plating bath temperature) to the plating solidification start temperature is not particularly limited, but the top roll etc. From the viewpoint of preventing the plating from winding around and suppressing appearance defects such as wind ripples, the temperature is preferably 0.5° C./s to 20° C./s.
However, the average cooling rate in the temperature range from the plating bath temperature to the plating solidification start temperature shall be a higher average cooling rate than the average cooling rate in the temperature range from the plating solidification start temperature to the plating solidification start temperature -30°C. As a result, the number of nucleation sites for Al crystals can be increased, and excessive coarsening of Al crystals can be suppressed.
[0097]
In addition, the average cooling rate in the temperature range from the plating solidification start temperature -30 ° C. to the plating solidification start temperature -300 ° C. is not particularly limited, but from the viewpoint of preventing the plating from winding around the top roll, etc., it is 0.5 C./s to 20.degree. C./s is preferable.
However, the average cooling rate in the temperature range from the plating solidification start temperature -30°C to the plating solidification start temperature -300°C is greater than the average cooling speed in the temperature range from the plating solidification start temperature to the plating solidification start temperature -30°C. Average cooling rate. As a result, excessive coarsening of Al crystals can be suppressed, and workability can be ensured.
[0098]
The Al--Fe alloy layer formed between the base steel material and the Zn--Al--Mg alloy layer rapidly forms and grows in less than one second immediately after immersion in the plating bath. The higher the plating bath temperature, the higher the growth rate, and the longer the immersion time in the plating bath, the higher the growth rate. However, when the temperature of the plating bath is less than 500° C., the growth hardly occurs. Therefore, it is better to shorten the immersion time or shift to the cooling process immediately after solidification.
[0099]
In addition, with regard to plated steel, once it is solidified, if it is reheated to remelt the plated layer, all the constituent phases will disappear.becomes a liquid phase. Therefore, for example, even a plated steel material that has undergone rapid cooling or the like once can be subjected to the structure control specified in the present disclosure in the process of reheating it off-line and performing an appropriate heat treatment. In this case, it is preferable that the reheating temperature of the plating layer is set in the vicinity of the melting point of the plating bath so that the Al—Fe alloy layer does not grow excessively.
[0100]
Post-treatments that can be applied to the plated steel material of the present disclosure will be described below.
[0101]
A film may be formed on the plating layer of the plated steel material of the present disclosure. The coating can form one layer or two or more layers. Examples of the types of films directly on the plating layer include chromate films, phosphate films, and chromate-free films. Chromate treatment, phosphate treatment, and chromate-free treatment for forming these films can be performed by known methods.
[0102]
Chromate treatment includes electrolytic chromate treatment, in which a chromate film is formed by electrolysis, reactive chromate treatment, in which a film is formed by using a reaction with the material, and then excess treatment liquid is washed away, and treatment liquid is applied to the object to be coated. There is a coating type chromate treatment that forms a film by drying without washing with water. Either process may be adopted.
[0103]
As electrolytic chromate treatment, electrolytic chromate treatment using chromic acid, silica sol, resin (acrylic resin, vinyl ester resin, vinyl acetate acrylic emulsion, carboxylated styrene-butadiene latex, diisopropanolamine-modified epoxy resin, etc.), and hard silica is used. can be exemplified.
[0104]
Examples of phosphate treatment include zinc phosphate treatment, zinc calcium phosphate treatment, and manganese phosphate treatment.
[0105]
Chromate-free treatment is particularly suitable because it does not burden the environment. Chromate-free treatment includes electrolytic-type chromate-free treatment that forms a chromate-free film by electrolysis, reaction-type chromate-free treatment that forms a film using reaction with the material, and then rinses off excess treatment liquid, and There is a coating-type chromate-free treatment in which a coating is applied to an object to be coated and dried without washing with water to form a film. Either process may be adopted.
[0106]
Furthermore, one layer or two layers or more of organic resin films may be provided on the film 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, modified products of these resins, and the like. Here, the modified product is a reaction of the reactive functional group contained in the structure of these resins with another compound (monomer, cross-linking agent, etc.) containing a functional group capable of reacting with the functional group in the structure. It refers to resin.
[0107]
As such an organic resin, one or two or more organic resins (unmodified) may be mixed and used, or in the presence of at least one organic resin, at least one other One or a mixture of two or more organic resins obtained by modifying the organic resin may be used. Further, the organic resin film may contain any color pigment or rust preventive pigment. A water-based product obtained by dissolving or dispersing in water can also be used.
Example
[0108]
Examples of the present disclosure will be described, but the conditions in the examples are one example of conditions adopted to confirm the feasibility and effect of the present disclosure, and the present disclosure is limited to this one example of conditions. not a thing Various conditions can be adopted for the present disclosure as long as the purpose of the present disclosure is achieved without departing from the gist of the present disclosure.
[0109]
(Example)
A predetermined amount of pure metal ingot was used to melt the ingot in a vacuum melting furnace so as to obtain a plating layer with the chemical composition shown in Tables 1 and 2, and then a plating bath was prepared in the atmosphere. A batch-type hot-dip plating apparatus was used to produce the plated steel sheets.
As the base steel material, a general material hot-rolled carbon steel sheet (C concentration <0.1%) with a thickness of 2.3 mm was used, and degreasing and pickling were performed immediately before the plating process.
In some examples, a pre-Ni-plated steel material obtained by applying pre-Ni-plating to a general-purpose hot-rolled carbon steel sheet having a thickness of 2.3 mm was used as the base steel material. The Ni adhesion amount was set to 1 g/m 2 to 3 g/m 2 . In addition, examples of using pre-Ni-plated steel as the base steel material are described as "pre-Ni" in the column of "base steel material" in the table, and the Ni concentration in the plating bath is written in parentheses in the column of Ni concentration. was written.
[0110]
In any sample preparation, the same reduction treatment method was applied to the base steel material until the time of immersion in the plating bath. That is, under an environment of N 2-H 2 (5%) (dew point of −40° C. or less, oxygen concentration of less than 25 ppm), the base steel material was heated from room temperature to 800° C. by electric heating, held for 60 seconds, and then N 2 It was cooled to a plating bath temperature of +10°C by gas blowing, and immediately immersed in the plating bath.
For all plated steel sheets, the immersion time in the plating bath was the time shown in the table. A plated steel sheet was produced by adjusting the N2 gas wiping pressure so that the plating thickness was 30 μm (±1 μm).
[0111]
The plating bath temperature was based on the melting point +20°C, and the temperature was further increased at some levels for plating. The plating bath immersion time was 2 seconds. After the base steel material was pulled up from the plating bath, a plating layer was obtained by a cooling process under the conditions shown in Tables 1 and 2 at average cooling rates in the following 1st to 3rd stages shown in Tables 1 and 2.
・First stage average cooling rate: Average cooling rate in the temperature range from the plating bath temperature to the plating solidification start temperature ・Second stage average cooling rate: Average temperature range from the plating bath temperature to the plating solidification start temperature -30°C cooling rate
・Third-stage average cooling rate: Temperature range average cooling rate from the plating solidification start temperature of -30°C to the plating solidification start temperature of -300°C
[0112]
－Various measurements－
A sample was cut out from the obtained plated steel sheet. Then, the following items were measured according to the method described above.
・Average value of cumulative perimeter length of Al crystal (denoted as “perimeter length of Al crystal” in the table)
・Area fraction of Al crystal
・Thickness of Al-Fe alloy layer (However, in the example of using a pre-Ni-plated steel sheet as the base steel material, the thickness of the Al-Ni-Fe alloy layer is shown.)
[0113]
－Corrosion resistance of flat part－
In order to compare the corrosion resistance of the flat part, the manufactured sample was subjected to an accelerated corrosion test (JASO M609-91) for 120 cycles, immersed in a 30% chromic acid aqueous solution at room temperature to remove white rust, and the corrosion resistance of the flat part was calculated from the corrosion weight loss. evaluated. The test was performed 5 times, and the average corrosion weight loss was 80 g / m 2 or less, and the maximum and minimum corrosion weight loss values ​​in n = 5 were within ± 100% of the average value. A case where the corrosion weight loss is 100 g/m 2 or less and the maximum and minimum values ​​of the corrosion weight loss in n = 5 are within ± 100% of the average value was evaluated as "A", and other than that was evaluated as "NG". .
[0114]
-Sacrificial corrosion resistance (corrosion resistance of cut edge)-
In order to compare the sacrificial corrosion resistance (corrosion resistance of the end face of the cut part), the sample was sheared to 50 mm x 100 mm, the upper and lower end faces were sealed, and the accelerated corrosion test (JASO M609-91) was performed for 120 cycles to expose the end face of the side part. The average value of the red rust generation area ratio of the part was evaluated. A red rust area rate of 50% or less was evaluated as "A+", 70% or less as "A", and more than 70% as "NG".
[0115]
- Workability -
　In order to evaluate the workability of the plating layer, the plated steel sheet was V-bent by 90°, a cellophane tape with a width of 24 mm was pressed against the valley of the V-bend and separated, and the powdering was visually evaluated. The evaluation was "A" when no powdering peeling powder adhered to the tape, "A-" when the powder was slightly adhered, and "NG" when the powder was adhered.
[0116]
-Discoloration resistance-
In order to evaluate discoloration resistance, the sample was sheared to 50 mm x 100 mm, all the samples were laminated with burrs aligned in the direction of the end face, wrapped in waterproof paper, and iron plates were laid on the top and bottom of the wrapped sample. , The four corners of the iron plate were fixed with bolts and nuts. When tightening the nut, a load of 12 N·m was applied with a torque wrench. Thereafter, the sample was placed in a constant temperature and humidity chamber (KCL-2000 manufactured by EYELA) at 50° C. and 80% RH, and the color difference after 7 days was evaluated. With respect to the color difference, the L value, a* value and b* value of the sample were measured with a colorimeter (Konica Minolta Optics CR-400) before and after the test to investigate the color difference ΔE.
Then, when ΔE was 3 or less, it was evaluated as "A+", when ΔE was more than 3 to 5 or less, it was evaluated as "A", and when ΔE was more than 5, it was evaluated as "NG".
[0117]
-Comprehensive evaluation-
"A" is an example in which each evaluation result of flat part corrosion resistance, sacrificial corrosion resistance, workability evaluation, and discoloration resistance evaluation is all "A", "A+" or "A-", even one is "NG" A certain thing was evaluated as "NG".
[0118]
Examples are listed in Tables 1 and 2.
[0119]
[Table 1-1]

[0120]
[Table 1-2]

[0121]
[Table 1-3]

[0122]
[Table 2-1]

[0123]
[Table 2-2]

[0124]
[Table 2-3]

[0125]
From the above results, it can be seen that the examples corresponding to the plated steel materials of the present disclosure have more stable flat surface corrosion resistance than the comparative examples.
In particular, it can be seen that the comparative example (test No. 50) in which the Sn concentration exceeds 0.2% has deteriorated discoloration resistance.
In addition, in the comparative example (Test No. 71) in which the average cooling rate was not changed to 15 ° C./s even if the chemical composition of the plating layer of the present disclosure was satisfied, the average value of the cumulative circumference length of the Al crystals became excessively large, It can be seen that stable flat surface corrosion resistance is not obtained.
On the other hand, a comparative example in which the average cooling rate in the second stage is excessively low (Comparative Example No. 72), a comparative example in which the average cooling rate was changed only in two stages (Test No. 73), and an average cooling rate of 6 ° C./s It can be seen that in the comparative example (test No. 74) that did not change, the average value of the cumulative circumference length of the Al crystal became excessively small, and the workability deteriorated.
In addition, the Ni concentration of the plating layer in the examples using pre-Ni-plated steel sheets (test Nos. 41 to 44) is more than 0.28% and 15% or less as detected by ICP analysis, so the Ni concentration of the plating layer is regarded as 0%.
[0126]
Although the preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, the present disclosure is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present disclosure belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. , are also understood to belong to the technical scope of the present disclosure.
[0127]
The explanation of the symbols is as follows.
Al: Al crystal
Zn-Al: Zn-Al phase
MgZn2: MgZn two-phase
Zn—Eu: Zn-based eutectic phase
[0128]
The disclosure of Japanese Patent Application No. 2019-205998 is incorporated herein by reference in its entirety.
All publications, patent applications and technical standards mentioned herein are to the same extent as if each individual publication, patent application and technical standard were specifically and individually noted to be incorporated by reference. incorporated herein by reference.

The scope of the claims

[Claim 1]
A plated steel material having a base steel material and a plating layer including a Zn-Al-Mg alloy layer disposed on the surface of the base steel material,
　The plating layer, in mass%,
Zn: more than 65.0%,
Al: more than 5.0% to less than 25.0%,
Mg: more than 3.0% to less than 12.5%,
Sn: 0 to 0.20%,
Bi: 0% to less than 5.0%,
In: 0% to less than 2.0%,
Ca: 0% to 3.0%,
Y: 0% to 0.5%,
La: 0% to less than 0.5%,
Ce: 0% to less than 0.5%,
Si: 0% to less than 2.5%,
Cr: 0% to 0.25%,
Ti: 0% to 0.25%,
Ni: 0% to 0.25%,
Co: 0% to 0.25%,
　V: 0% to 0.25%,
Nb: 0% to 0.25%,
Cu: 0% to 0.25%,
Mn: 0% to 0.25%,
Fe: 0% to 5.0%,
Sr: 0% to less than 0.5%,
Sb: 0% to less than 0.5%,
Pb: 0% to less than 0.5%,
　B: 0% ~less than 0.5%, and
has a chemical composition consisting of impurities,
A backscattered electron image of the Zn-Al-Mg alloy layer obtained by polishing the surface of the Zn-Al-Mg alloy layer to 1/2 of the layer thickness and then observing with a scanning electron microscope at a magnification of 100. 3. A plated steel material in which Al crystals are present and the average value of the cumulative perimeter of the Al crystals is 88 to 195 mm/mm 2 .
[Claim 2]
The plated steel material according to claim 1, wherein the Sn content is 0 to less than 0.10% by mass.
[Claim 3]
The plated steel material according to claim 1 or claim 2, wherein the plated layer has an Al-Fe alloy layer with a thickness of 0.05 to 5 µm between the base steel material and the Zn-Al-Mg alloy layer.