Seawater-resistant plated steel material and manufacturing method therefor

Abstract

A seawater-resistant plated steel material according to an embodiment of the present invention comprises: a steel material containing, in weight%, 0.5 to 1.5% of Cr and 0.1 to 1.0% of Cu; and a zinc-based plating layer present on the steel material, wherein the zinc-based plating layer has an area fraction of pores therein of 0.5 to 1.5%.

Description

Seawater-resistant plated steel and method of manufacturing the same

[0001] One embodiment of the present invention relates to a seawater-resistant plated steel and a method for manufacturing the same. More specifically, one embodiment of the present invention relates to a seawater-resistant plated steel and a method for manufacturing the same, comprising a seawater-resistant steel and a heavy-duty coating system based on the steel's characteristics to improve durability in a seawater environment.

[0002] In marine environments, structural steel is used in various forms, such as piles supporting harbors, cranes, and sluice gates. Steel exposed to the extremely corrosive marine environment generally uses heavy-duty coatings to prevent corrosion; however, since facilities utilizing steel are typically used semi-permanently, it is common practice to maintain the facilities by performing maintenance due to frequent damage or deterioration of the applied heavy-duty coatings during long-term operation.

[0003] In the past, on-site maintenance of paintwork was relatively easy; however, due to recent factors such as the strengthening of industrial safety laws and rising labor costs, performing maintenance on-site has become very unfavorable in terms of legal issues and economic feasibility. Consequently, there is a growing demand for methods that do not require long-term maintenance from the time of initial installation.

[0004] Generally, ordinary carbon steel is the most widely used structural steel for marine environments, and while it varies depending on the application environment, organic heavy-duty coatings are applied for protection. In such systems, the coating layer is destroyed if it deteriorates due to UV rays and seawater, or if it is scratched by suspended particles; therefore, most technologies have been developed to enhance the durability of the paint itself and improve scratch resistance. In this case, the steel has been approached solely from the perspective of structural properties, and it is common for it to be designed in a way that contributes little to the overall system from a durability standpoint.

[0005] Seawater-resistant steel is a material created by adding Cr and Cu to a composition similar to general carbon steel, resulting in slower corrosion compared to general carbon steel in seawater environments, particularly in splash zones. Due to this reduced corrosion rate, when used as a structural material in seawater environments, this steel allows for a lighter design by reducing the corrosion margin thickness required for the design life compared to general carbon steel. Another characteristic of this steel is that it exhibits a lower galvanic current density than general carbon steel.

[0006] One embodiment of the present invention provides a seawater-resistant plated steel and a method for manufacturing the same. More specifically, one embodiment of the present invention provides a seawater-resistant plated steel and a method for manufacturing the same, comprising a seawater-resistant steel and a heavy-duty coating system based on the steel's characteristics to improve durability in a seawater environment.

[0007] A seawater-resistant plated steel according to one embodiment of the present invention comprises a steel containing Cr: 0.5 to 1.5% and Cu: 0.1 to 1.0% by weight, and a zinc-based plating layer present on the steel, wherein the zinc-based plating layer has an area ratio of pores within the zinc-based plating layer of 0.5 to 1.5%.

[0008] The steel may further contain, in weight percent, C: 0.1% or less, Si: 0.5% or less, Mn: 1.0% or less, P: 0.03% or less, S: 0.015% or less, the remainder being Fe and unavoidable impurities.

[0009] The zinc-based plating layer may include at least one of Zn, Mg, Al, and Ni.

[0010] The zinc-based plating layer may contain 10 to 30 weight percent of Al and the remainder being Zn.

[0011] The zinc-based plating layer may have a thickness of 100 to 150 μm.

[0012] The average particle size of the pores in the zinc-based plating layer may be 1 to 5 μm.

[0013] The area ratio of pores in the zinc-based plating layer may be 0.5 to 1.0%.

[0014] A seawater-resistant plated steel according to one embodiment of the present invention may further include a coating layer located on a zinc-based plating layer.

[0015] The coating layer may include one or more types of siloxane-based resins and epoxy-based resins.

[0016] The thickness of the coating layer may be 40 to 80 μm.

[0017] A method for manufacturing a seawater-resistant plated steel according to one embodiment of the present invention comprises the steps of: preparing a steel containing Cr: 0.5 to 1.5% and Cu: 0.1 to 1.0% by weight; and forming a zinc-based plating layer on the surface of the steel using an arc spraying method, wherein the voltage is adjusted to 30V or higher in the step of forming the zinc-based plating layer.

[0018] In the step of forming a zinc-based plating layer, the robot pitch can be adjusted to 10 mm or more.

[0019] After the step of forming a zinc-based plating layer, the method may further include the step of forming a coating layer on the zinc-based plating layer.

[0020] A seawater-resistant plated steel according to one embodiment of the present invention improves the durability of steel structures and extends the coating life.

[0021] Figure 1 is a photograph of a cross-section of a zinc-based plating layer prepared in Example 1, observed with an optical microscope.

[0022] Figure 2 is a photograph of a cross-section of the zinc-based plating layer prepared in Example 2, observed with an optical microscope.

[0023] Figure 3 is a photograph of a cross-section of a zinc-based plating layer prepared in Comparative Example 1, observed with an optical microscope.

[0024] Figure 4 is a photograph of the seawater-resistant plated steel prepared in Example 2 after an accelerated aging corrosion test.

[0025] Figure 5 is a photograph of the seawater-resistant plated steel manufactured in Comparative Example 1 after an accelerated aging corrosion test.

[0026] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0027] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0028] When it is stated that one part is "above" or "on" another part, it may be directly above or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly above" another part, no other part is interposed in between.

[0029] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0030] In one embodiment of the present invention, the meaning of including additional elements is that the remainder of iron (Fe) is replaced by an amount of the additional element.

[0031] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0032] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0033]

[0034] A seawater-resistant plated steel according to one embodiment of the present invention comprises a steel containing Cr: 0.5 to 1.5% and Cu: 0.1 to 1.0% by weight, and a zinc-based plating layer present on the steel, wherein the zinc-based plating layer has an area ratio of pores within the zinc-based plating layer of 0.5 to 1.5%.

[0035] In one embodiment of the present invention, the steel is a seawater-resistant steel, and by appropriately including Cr and Cu, a steel having the characteristic of corroding more slowly than general carbon steel in a seawater environment, particularly in a splash zone environment, can be used. More specifically, it may include 0.7 to 1.2 weight% of Cr and 0.3 to 0.7 weight% of Cu.

[0036] Regarding the remaining steel components, the steel may further contain, in weight percent, C: 0.1% or less, Si: 0.5% or less, Mn: 1.0% or less, P: 0.03% or less, S: 0.015% or less, the remainder being Fe and unavoidable impurities. Since the effect of one embodiment of the present invention is achieved by the characteristics of the zinc-based plating layer, a specific description of the steel components of the steel is omitted.

[0037] The aforementioned steel also possesses the characteristic of having a low galvanic current density. When this characteristic is applied to the design of a coating material that protects the steel, it is possible to manufacture a system in which the failure rate of the coating layer is significantly slower than that of general steel. Non-ferrous coatings using arc spraying in a seawater environment offer superior durability compared to organic coatings; however, securing long-term durability requires a very thick coating, and consequently, the process cost is relatively high compared to organic coatings, making it a method with limited application. However, when applied to seawater-resistant steel, the consumption rate of the coating layer is slower than that of general steel, allowing for sufficient durability even with a relatively thin coating layer. Furthermore, it is possible to reduce process costs, thereby providing a technique with superior durability and economic efficiency compared to organic coating methods.

[0038] In one embodiment of the present invention, a zinc-based plating layer exists on a steel material. The zinc-based plating layer is a plating layer containing Zn, and may include at least one of Mg, Al, and Ni in addition to Zn. More specifically, the zinc-based plating layer may contain 10 to 30 weight percent of Al and the remainder being Zn.

[0039] In one embodiment of the present invention, a zinc-based plating layer exists on a steel material, and the area ratio of pores within the zinc-based plating layer is 0.5 to 1.5%. The area ratio of pores within the zinc-based plating layer is inevitably present, and if the pore area is too large, the adhesion strength between the steel material and the zinc-based plating layer decreases, which can significantly reduce durability. More specifically, the area ratio of pores within the zinc-based plating layer may be 0.5 to 1.0%. The area ratio of pores can be calculated by observing a cross-section including the thickness direction of the zinc-based plating layer using an optical microscope and utilizing a porosity image analyzer program. At this time, the magnification can be set to 500x. In the observed photograph, a color value L of -70 or less can be determined as a pore. In one embodiment of the present invention, pores are considered not only as empty spaces within the zinc-based plating layer, but also as cases where empty spaces are partially filled with a material other than the plating material, such as a coating material.

[0040] The average particle size of pores within the zinc-based plating layer may be 1 to 5 µm. If the average particle size is too small, it is difficult to identify them as pores using an image analyzer, and in this case, it can be said that a dense coating layer has been well formed. If the average particle size is too large, the plating layer itself has very large pores, so it cannot function as a coating layer, and problems may arise where it easily detaches from the base material due to mechanical frictional wear. More specifically, the average particle size of the pores may be 1.5 to 3.5 µm. The average particle size of the pores can be calculated by assuming a virtual circle with an area equal to the area occupied by the pores and determining the diameter of that circle. Due to measurement limits, the minimum particle size is 1 µm, and the average refers to the numerical average.

[0041] The zinc-based plating layer may have a thickness of 100 to 150 μm. If the thickness of the zinc-based plating layer is too thin, corrosion resistance may be a problem. In one embodiment of the present invention, corrosion resistance is improved by forming fewer pores, so a thickness exceeding the aforementioned range may be unnecessary. More specifically, the thickness may be 130 to 150 μm.

[0042] A coating layer located on a zinc-based plating layer according to one embodiment of the present invention may be further included. The coating layer can protect the zinc-based plating layer to further improve durability. As the coating layer, one or more types selected from siloxane-based resins and epoxy-based resins may be included. These resins have low viscosity and can further improve corrosion resistance by filling the pores within the aforementioned zinc-based plating layer. As the coating layer, the viscosity is 1000 mm based on kinematic viscosity (25°C). 2 Substances with a value of / s(1000cST) or less may be used.

[0043] The thickness of the coating layer may be 40 to 80 µm. If the coating layer is too thin, it may be damaged quickly by ultraviolet rays and seawater. If the coating layer is too thick, there is a risk of peeling. More specifically, the thickness of the coating layer may be 45 to 70 µm.

[0044]

[0045] A method for manufacturing a seawater-resistant plated steel according to one embodiment of the present invention comprises the steps of: preparing a steel containing Cr: 0.5 to 1.5% and Cu: 0.1 to 1.0% by weight; and forming a zinc-based plating layer on the surface of the steel using an arc spraying method, wherein the voltage is adjusted to 30V or higher in the step of forming the zinc-based plating layer.

[0046] First, prepare a steel containing Cr: 0.5 to 1.5% and Cu: 0.1 to 1.0% by weight. Since the steel has been described above, a redundant explanation is omitted.

[0047] Next, a zinc-based plating layer is formed on the surface of the steel using an arc spraying method. Since the arc spraying method is widely known, a detailed explanation thereof is omitted. In one embodiment of the present invention, by adjusting the voltage applied to the arc gun during the arc spraying process to 30V or higher, fewer pores can be formed in the zinc-based plating layer. More specifically, the voltage can be adjusted to 31 to 35V.

[0048] Regarding conditions other than voltage, the current can be specifically adjusted to 100 to 300 A, the air (Primary Air) pressure to 45 to 55 psi, the arc jet to 55 to 65 psi, the spraying distance to 100 to 200 mm, and the gun speed to 400 to 600 mm / sec.

[0049] In addition, the robot pitch can be adjusted to 10 mm or more. The robot pitch refers to the distance between the substrate being coated and the arc gun. More specifically, it can be 15 to 25 mm.

[0050] After the step of forming a zinc-based plating layer, the method may further include the step of forming a coating layer on the zinc-based plating layer.

[0051]

[0052] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0053]

[0054] Example 1

[0055] A seawater-resistant steel containing 1 wt% Cr and 0.5 wt% Cu was prepared.

[0056] A plating layer with a thickness of 150㎛ was formed on the surface of steel using an arc spraying method under conditions of an arc gun voltage of 32V, current of 200A, air of 50psi, arc jet of 60psi, spraying distance of 150mm, gun speed of 500mm / sec, and robot pitch of 20mm, and with a wire type of 85%Zn-15%Al.

[0057] Afterwards, a coating layer made of siloxane resin was formed to a thickness of 50 μm.

[0058] A cross-section of the zinc-based plating layer was observed at 500x magnification using an optical microscope and is shown in Fig. 1.

[0059] As shown in Figure 1, it can be confirmed that the pore area is 1.423% and the average pore size is 3㎛.

[0060] Example 2

[0061] The same as in Example 1 was carried out, but the robot pitch was adjusted to 10 mm during the arc spraying process and the wire type was 85%Zn-15%Al.

[0062] A cross-section of the zinc-based plating layer was observed at 500x magnification using an optical microscope and is shown in Fig. 2.

[0063] As shown in Figure 2, it can be confirmed that the pore area is 0.750% and the average pore size is 1㎛.

[0064] Durability characteristics were tested using the accelerated aging test method consisting of UV, salt spray, and thermal shock cycles according to ISO 12994-6 and NORSOK M 501. A photograph taken after the experiment is shown in Fig. 4.

[0065] As shown in Figure 4, it can be confirmed that the corrosion failure of the paint layer is slow.

[0066] Comparative Example 1

[0067] The same as in Example 1 was used, but the voltage during the arc spraying process was set to 28V, the robot pitch to 10mm, and the wire type to 85%Zn-15%Al.

[0068] A cross-section of the zinc-based plating layer was observed at 500x magnification using an optical microscope and is shown in Fig. 3.

[0069] As shown in Figure 3, it can be confirmed that the pore area is 2.357% and the average pore size is 5㎛.

[0070] Durability characteristics were tested using the accelerated aging test method consisting of UV, salt spray, and thermal shock cycles according to ISO 12994-6 and NORSOK M 501. A photograph taken after the experiment is shown in Fig. 5.

[0071] As shown in Figure 5, it can be confirmed that the corrosion failure of the paint layer is very rapid.

[0072]

[0073] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Steel containing Cr: 0.5 to 1.5% and Cu: 0.1 to 1.0% by weight, and It includes a zinc-based plating layer present on the above steel material, and The above zinc-based plating layer is a seawater-resistant plated steel material having a pore area ratio of 0.5 to 1.5% within the zinc-based plating layer.

2. In Paragraph 1, The above steel is a seawater-resistant plated steel comprising, in weight%, C: 0.1% or less, Si: 0.5% or less, Mn: 1.0% or less, P: 0.03% or less, S: 0.015% or less, and the remainder being Fe and unavoidable impurities.

3. In Paragraph 1 or 2, The above zinc-based plating layer is a seawater-resistant plated steel containing at least one of Zn, Mg, Al, and Ni.

4. In any one of paragraphs 1 through 3, The above zinc-based plating layer is a seawater-resistant plated steel containing 10 to 30 weight% of Al and the remainder of Zn.

5. In any one of paragraphs 1 through 4, The above zinc-based plating layer is a seawater-resistant plated steel with a thickness of 100 to 150 μm.

6. In any one of paragraphs 1 through 5, Seawater-resistant plated steel having an average particle size of pores in the zinc-based plating layer of 1 to 5 μm.

7. In any one of paragraphs 1 through 6, Seawater-resistant plated steel having a pore area ratio of 0.5 to 1.0% in the zinc-based plating layer.

8. In any one of paragraphs 1 through 7, Seawater-resistant plated steel further comprising a coating layer located on the above zinc-based plating layer.

9. In Paragraph 8, The above coating layer is a seawater-resistant plated steel material comprising one or more types of siloxane-based resins and epoxy-based resins.

10. In Paragraph 8 or 9, Seawater-resistant plated steel having a coating layer thickness of 40 to 80 μm.

11. A step of preparing a steel material comprising Cr: 0.5 to 1.5% and Cu: 0.1 to 1.0% by weight; and The method includes the step of forming a zinc-based plating layer on the surface of the steel using an arc spraying method. A method for manufacturing seawater-resistant plated steel by adjusting the voltage to 30V or higher in the step of forming the zinc-based plating layer.

12. In Paragraph 11, A method for manufacturing seawater-resistant plated steel, wherein the robot pitch is controlled to be 10 mm or more in the step of forming the zinc-based plating layer.

13. In Paragraph 11 or 12, A method for manufacturing seawater-resistant plated steel, comprising, after the step of forming the zinc-based plating layer, the step of forming a coating layer on the zinc-based plating layer.

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