Patent Application
20220025508
The present disclosure relates to a coated steel sheet that may be used in vehicles, home appliances, construction materials, and the like, and more particularly, to a heterogeneous coated steel sheet having a zinc coating layer formed on one surface thereof and a zinc-magnesium coating layer formed on the other surface thereof.
The surface treatment technique is a technique for plating the surface of a steel sheet to suppress corrosion of the steel sheet, and a zinc-coated steel sheet using zinc is representative. As a method for manufacturing such a galvanized steel sheet, typically, electrical or hot-dip galvanizing has been utilized.
As illustrated in
The galvanized steel sheet is soft due to low hardness of the coating layer, and thus, may be easily damaged by external stress during coil transport, and there is a problem in which workability is degraded due to a phenomenon (galling) of zinc sticking to the die during processing. In addition, since the surface friction coefficient is great, it is difficult to apply the galvanized steel sheet to automotive steel sheets subjected to severe processing and having many welding parts.
In order to prevent such a problem, zinc alloy plated steel sheets have emerged, and representatively, alloyed hot-dip galvanized steel sheets and zinc-aluminum alloy plated steel sheets have been introduced.
The alloyed hot-dip galvanized steel sheet is excellent in paintability of coating film adhesion and weldability of electrode lifespan due to formation of Fe—Zn intermetallic compound by alloying reaction of base iron and a galvanized layer. However, due to an Fe—Zn alloy phase (gamma phase) generated by the alloying reaction, there is a problem in workability due to powdering in which the plating layer falls during processing of a steel sheet. In addition, when a sealer used for waterproofing, corrosion prevention, vibration absorption, and welding is attached to a steel sheet, there is a problem in that an Fe—Zn plating layer falls off after bonding the sealer due to an alloy phase generated between Fe—Zn. In addition, since the surface of the Fe—Zn plating layer is not beautiful and the whiteness is not high, it may be difficult to apply as a steel sheet for home appliances, requiring a beautiful surface even after painting or used without painting.
On the other hand, in the case of zinc-aluminum (Zn—Al) alloy plating, since it is difficult to prepare an electroplating solution, manufacturing the zinc-aluminum alloy plated steel sheet by an electroplating method may be difficult, and in the case of manufacturing using a hot-dip plating method, forming different plating layers on both surfaces of a steel sheet may be difficult.
An aspect of the present disclosure is to provide a heterogeneous coated steel sheet, in which one side of a steel sheet is coated with zinc and the other side thereof is coated with a zinc-magnesium alloy, and which has excellent workability and corrosion resistance, and a method of manufacturing the same.
The subject of the present disclosure to be solved is not limited to the above matters. Additional subjects of the present disclosure are described in the overall content of the specification, and those of ordinary skill in the art to which the present disclosure pertains will have no difficulty in understanding the additional subjects of the present disclosure from the contents described in the specification of the present disclosure.
According to an aspect of the present disclosure, a heterogeneous coated steel sheet having excellent workability and corrosion resistance, includes a steel sheet; a zinc coating layer attached to one side of the steel sheet; and a zinc-magnesium alloy coating layer attached to the other side of the steel sheet. A coating adhesion amount of the zinc coating layer is 5-60 g/m2, a coating adhesion amount of the zinc-magnesium alloy coating layer is 10 to 40 g/m2, and a magnesium content of the zinc-magnesium alloy coating layer is 8 to 30 wt %.
According to another aspect of the present disclosure, a method of manufacturing a heterogeneous coated steel sheet having excellent workability and corrosion resistance, includes preparing a steel sheet; levitating a coating material by electromagnetic force in a vacuum chamber to generate zinc deposition vapor, and forming a zinc coating layer having an adhesion amount of 5 to 60 g/m2 on one surface of the steel sheet by inducing and ejecting the zinc deposition vapor; and generating zinc-magnesium alloy deposition vapor by levitating a coating material by electromagnetic force in a vacuum chamber, and forming a zinc-magnesium alloy coating layer having an adhesion amount of 10 to 40 g/m2 on the other surface of the steel sheet by inducing and ejecting the zinc-magnesium alloy deposition vapor. A Mg content contained in the zinc-magnesium alloy deposition vapor is 8 to 30 weight %.
According to an exemplary embodiment, there is provided a heterogeneous coated steel sheet in which one side of a steel sheet is provided with a zinc coating layer thereon, and the other side thereof is provided with a zinc-magnesium alloy coating layer thereon. In detail, there is provided a heterogeneous coated steel sheet in which excellent workability and corrosion resistance may be secured by optimizing a coating amount of the zinc coating layer and a composition of the zinc-magnesium alloy coating layer.
There is provided a heterogeneous coated steel sheet having further excellent workability and corrosion resistance than a coated steel sheet in which both sides of a related art steel sheet are coated with zinc or a zinc alloy. In this case, the heterogeneous steel sheet indicates that one side and the other side of the steel sheet are coated with different kinds of materials, so that respective sides of the steel sheet have different coating layers in one coating steel sheet.
The inventors of the present disclosure have contemplated manners to economically produce products while ensuring corrosion resistance and workability by forming a Zn—Mg coating layer required for products that require high corrosion resistance and galling resistance, compared to the existing coated steel sheet having the same material on both sides, and by forming a zinc coating layer for temporary rust prevention on the other side thereof corresponding to the service coating. To obtain the above effect, a heterogeneous coated steel sheet in which a zinc coating layer is formed on one side of the steel sheet and a zinc-magnesium alloy coating layer is formed on the other side thereof has been derived.
Hereinafter, a heterogeneous coated steel sheet according to an exemplary embodiment will be described in detail with reference to the accompanying drawings. The accompanying drawings are only for understanding of the present disclosure, and are not intended to limit the present disclosure.
As illustrated in
In the present disclosure, the steel sheet 200 may be a hot-rolled steel sheet, a cold-rolled steel sheet, an annealed steel sheet, or the like that may be used for home appliances, building materials, automobiles, and the like, and the use and type thereof are not particularly limited.
The zinc coating layer 210 attached to one surface of the steel sheet 210 may preferably have an average grain size of 500 to 800 nm, which is a level of ⅓ of the grain size of an electro-galvanized steel sheet of the related art. Due to the fine grain size thereof, high angle pyramidal surfaces ((103), (102) and (101) surfaces) and a prism (110) surface may be relatively developed and first cultured. A coating adhesion amount of the zinc coating layer 210 may preferably be 5 to 60 g/m2, more preferably 10 to 60 g/m2. If the coating adhesion amount of the zinc coating layer is less than 5 g/m2, there is a problem in which the corrosion resistance of the steel sheet as temporary rust prevention cannot be guaranteed, and if the coating adhesion amount thereof exceeds 60 g/m2, it may act disadvantageously in terms of productivity and workability of the zinc coating layer. Therefore, the coating adhesion amount of the zinc coating layer may preferably be 5-60 g/m2.
The zinc-magnesium alloy coating layer 220 attached to the other side of the steel sheet 210 may preferably contain 8 to 30% by weight of magnesium (Mg), and the balance of Zn and unavoidable impurities. If the Mg content is less than 8% by weight, the surface appearance may be defective due to color non-uniformity on the surface of the steel sheet, and if it exceeds 30% by weight, there is no advantage in corrosion resistance, economy and workability.
The corrosion potential of the zinc-magnesium alloy coating layer 220 is −1.07V to −1.13V (SCE, Saturated Calomel Electrode), which exhibits a high corrosion potential compared to the existing zinc-iron alloy coated steel sheet (−0.89V SCE) and zinc coating steel sheet (−1.03V SCE), thereby securing excellent corrosion resistance.
On the other hand, it may be preferable that the coating adhesion amount of the zinc-magnesium alloy coating layer 220 is 10 to 40 g/m2. If the coating adhesion amount of the zinc-magnesium alloy coating layer is less than 10 g/m2, excellent corrosion resistance may not be secured, and if it exceeds 40 g/m2, workability is reduced due to powdering properties of the coating layer, which may not be preferable. The zinc-magnesium alloy coating layer 220 is not limited to one layer, and may be formed in a multilayer structure of two or more layers.
The coating structure of the zinc-magnesium alloy coating layer 220 may include various alloy phases, such as Zn single phase, Mg single phase, Mg2Zn11 alloy phase, MgZn2 alloy phase, MgZn alloy phase, Mg7Zn3 alloy phase, and the like, depending on a composition of magnesium, and fractions of the alloy phases may also differ from each other.
The heterogeneous coated steel sheet according to an exemplary embodiment of the present disclosure provides a coating layer of various structures, in consideration of various usage patterns, uses and the like in composing the zinc-magnesium alloy coating layer, and thus, surface appearance, corrosion resistance, galling resistance, weldability and the like may be secured. For example, by including a Zn layer on the upper and/or lower portion of the zinc-magnesium alloy coating layer, a structure of two to three layers or more may be provided.
For example,
In
On the other hand, in
Hereinafter, a method of manufacturing a heterogeneous coated steel sheet according to another embodiment of the present disclosure will be described in detail.
First, a steel sheet is prepared. A process of removing foreign substances, oxide films, or the like that may be present on the surface of the steel sheet, may be included. For example, after degreasing, rinsing, and drying using a 2% or more of low-temperature complex degreasing agent or alkaline degreasing solution, a process of removing foreign substances and natural oxide films on the surface may be performed using plasma and ion beams or the like.
A zinc coating layer is formed on one side of the steel sheet to have a coating adhesion amount of 5 to 60 g/m2, and a zinc-magnesium alloy coating layer is formed to have a coating adhesion amount of 10 to 40 g/m2 on the other side of the steel sheet. There is no difference in the formation order of the zinc coating layer and the zinc-magnesium alloy coating layer.
The zinc coating layer and the zinc-magnesium alloy coating layer may be preferably formed by an electromagnetic heating physical vapor deposition method having an electromagnetic stirring effect.
To manufacture a coated steel sheet, a physical vapor deposition (PVD) process is used in a vacuum. The disadvantage of the related art PVD process is that the coating material to be vaporized is always present in a liquid state due to the high processing temperature, and thus, the coating speed is limited. For example, in the case of electron beam evaporation using an electron gun, the coating material should be placed in a crucible made of ceramic or copper. In the case of a copper crucible, care should be taken not to melt the copper due to intensive cooling with water or not to vaporize the copper at the same time. A disadvantage of cooling the copper crucible is that a significant amount of heat is lost due to the cooling operation. The use of ceramic crucibles is limited to a coating material that does not chemically react with the material of the crucible at a relatively high temperature. In addition, since most ceramic crucibles have relatively low thermal conductivity, there is a problem in supplying required thermal energy. Therefore, the manufacturing method of the present disclosure may be preferably performed by an electromagnetic heating physical vapor deposition method.
The electromagnetic heating physical vapor deposition method may be performed using a phenomenon, in which when high-frequency power is applied to an electromagnetic coil that generates an alternating magnetic field in a vacuum chamber to generate electromagnetic force, a coating material (zinc, magnesium or the like) is levitated in the air without external help in a space surrounded by an alternating electromagnetic field, and the levitated coating material generates a large amount of metal vapor (zinc deposition vapor, zinc and magnesium deposition vapor).
On the other hand, the Mg content contained in the zinc-magnesium alloy deposition vapor may preferably be 8 to 30% by weight.
The method may further include a process of forming a zinc layer before and/or after forming the zinc-magnesium alloy coating layer. The zinc layer may preferably be formed by an electromagnetic heating physical vapor deposition method.
The heterogeneous plated steel sheet of the present disclosure obtained by the above method has a significantly fine grain size compared to the related art plated steel sheet, and thus, and has an advantage that the surface appearance is beautiful, the workability is improved due to the increase in hardness, and the corrosion resistance by a Zn—Mg alloy phase due to the Mg content is greatly improved.
Hereinafter, embodiments of the present disclosure will be described in detail. The following examples are only for the understanding of the present disclosure, and are not intended to limit the scope of the present disclosure.
A cold-rolled steel sheet including, by weight %, C: 0.125%, Si: 0.102%, Ti: 0.019%, Cu: 0.012%, and the balance of Fe and unavoidable impurities, and having a thickness of 1.20 mm, was prepared. By using the apparatus of
On the other hand, in Table 1, a related art example is a zinc coating steel sheet manufactured by an electrogalvanizing or hot dip plating method.
For the coated steel sheet manufactured as described above, corrosion resistance, powdering properties, and galling properties were evaluated, and the results are illustrated together in Table 1.
For corrosion resistance, the corrosion resistance was evaluated after cutting the coated steel sheet into 75 mm×150=specimens and processing flat plate and cup drawing thereon. In accordance with JIS Z 2371, a salt spray test was conducted to record the time of initial occurrence of red rust, and the relative comparison evaluation with the hot-dip galvanized steel sheet (GI) of 60 g/m2 based on the coating adhesion amount on one side was performed. The criteria are as follows.
1: Excellent
2: Normal (GI 60 g/m2) level
3: Defective
For powdering properties, a specimen obtained by cutting a coated steel sheet into a width of 40 mm and a length of 80 mm was mounted on a press tester and subjected to a 60° bending test. After detaching the specimen from the tester and attaching the cellophane tape to the bent part, the tape was unfolded and removed, and then, the tape was attached to a white paper, and the peeling width was measured for comparative evaluation. The criteria are as follows.
1: Excellent (peel width: less than 6.0 mm)
2. Normal (peel width: 6.0-8.0 mm)
3: Defective (peel width: exceeding 8.0 mm)
On the other hand, the galling properties were compared and evaluated by measuring a total of 40 times (120° rotation per rotation) using a rotational friction tester on a specimen obtained by cutting a coated steel sheet into 200 mm×200 mm sizes. The friction coefficient value compared to the initial (before the rotational friction test) was compared and evaluated when the rotation was continuously performed using a rotational friction tester, and the criteria are as follows.
1: Excellent (the coefficient of friction after 30 rotations increased by less than 20% compared to the initial value)
2: Normal (the coefficient of friction after 30 rotations increased by less than 40% compared to the initial value)
3: Defective (the coefficient of friction after 30 rotations increased by 50% or more compared to the initial value)
The surface appearance was provided by comparing and evaluating Delta E values obtained by measuring L (whiteness), a (Red-Green), and b (Yellow-Blue) using a color difference meter on specimens cut in size of 600=×1000 mm. The criteria are as follows.
1: Excellent (Delta E 3 or less between measurement portions within the full width/full length of the coated steel sheet)
2: Normal (Delta E 5 or less between measurement portions within the full width/full length of the coated steel sheet)
3: Defective (exceeding Delta E 5 between measurement portions within the full width/length of the coated steel sheet)
In the ‘coating layer composition’ in Table 1, Zn/Zn—Mg, Zn—Mg/Zn, and Zn/Zn—Mg/Zn refer to a coating layer having a multi-layer structure, and indicates that it is formed from the surface of the steel sheet. For example, Zn/Zn—Mg indicates that a zinc (Zn) layer is formed and a zinc-magnesium alloy (Zn—Mg) layer is formed thereon, from the surface of the steel sheet.
In the case of the related art, it can be seen that, due to the ductility of zinc, zinc adheres to the mold during continuous molding and the friction coefficient increases, resulting in poor galling resistance and poor corrosion resistance.
Meanwhile, Comparative Examples 1 to 6 correspond to a heterogeneous coated steel sheet of a zinc coating layer and a zinc-magnesium alloy coating layer, and may have the case of satisfactory tendency depending on the composition ratio of adhesion amount of the coating layer, but it can be seen that all conditions cannot be uniformly satisfied. On the other hand, in the case of Comparative Examples 3 and 5, the Mg content of the zinc-magnesium alloy coating layer did not meet the conditions presented in the present disclosure, and thus, it can be confirmed that the surface appearance characteristics are inferior. In the case of Comparative Example 4, all properties were illustrated to be good, but due to an excessive adhesion amount of coating, workability was lowered and there was a disadvantage in terms of costs, and thus, this case was classified as a comparative example.
Inventive Examples 1 to 11 are heterogeneous coated steel sheets having a zinc coating layer and a zinc-magnesium alloy coating layer, and the coating adhesion amount and Mg content are appropriately adjusted, and it can be confirmed that the overall properties are evenly superior to those of the related art examples or comparative examples.
On the other hand, Inventive Examples 9 to 11 illustrate the case in which the zinc-magnesium alloy coating layer and the zinc layer form a multilayer structure. In the case of Inventive Examples 9-1 and 11-1, it can be seen that the adhesion amount of the zinc layer between the steel sheet and the zinc-magnesium alloy coating layer was low, and thus, the powdering properties were somewhat deteriorated. In the case of Inventive Examples 10-3 and 11-4, it can be seen that the adhesion amount of the zinc layer present on the zinc-magnesium alloy coating layer was slightly excessive, and thus, the galling resistance was slightly lowered. Inventive Examples 10-1 and 11-3 are cases in which the adhesion amount of the zinc layer present on the zinc-magnesium alloy coating layer is small, and blackening resistance may be inferior.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2018-0165283 | Dec 2018 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2019/018099 | 12/19/2019 | WO | 00 |
