US20180320260A1 - Zinc alloy plated steel sheet having excellent bending workability and manufacturing method therefor - Google Patents

Zinc alloy plated steel sheet having excellent bending workability and manufacturing method therefor Download PDF

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US20180320260A1
US20180320260A1 US15/770,615 US201615770615A US2018320260A1 US 20180320260 A1 US20180320260 A1 US 20180320260A1 US 201615770615 A US201615770615 A US 201615770615A US 2018320260 A1 US2018320260 A1 US 2018320260A1
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zinc alloy
steel sheet
plated steel
alloy plated
single phase
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Min-Suk Oh
Sang-Heon Kim
Tae-Chul Kim
Jong-sang Kim
Hyun-Chu YUN
Bong-Hwan Yoo
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Posco Holdings Inc
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Posco Co Ltd
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Priority claimed from PCT/KR2016/012098 external-priority patent/WO2017074030A1/ko
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/14—Removing excess of molten coatings; Controlling or regulating the coating thickness
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/14—Removing excess of molten coatings; Controlling or regulating the coating thickness
    • C23C2/16—Removing excess of molten coatings; Controlling or regulating the coating thickness using fluids under pressure, e.g. air knives
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/14—Removing excess of molten coatings; Controlling or regulating the coating thickness
    • C23C2/16—Removing excess of molten coatings; Controlling or regulating the coating thickness using fluids under pressure, e.g. air knives
    • C23C2/18—Removing excess of molten coatings from elongated material
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/14—Removing excess of molten coatings; Controlling or regulating the coating thickness
    • C23C2/16—Removing excess of molten coatings; Controlling or regulating the coating thickness using fluids under pressure, e.g. air knives
    • C23C2/18—Removing excess of molten coatings from elongated material
    • C23C2/20—Strips; Plates
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/261—After-treatment in a gas atmosphere, e.g. inert or reducing atmosphere
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C18/00—Alloys based on zinc
    • C22C18/04—Alloys based on zinc with aluminium as the next major constituent
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12771—Transition metal-base component
    • Y10T428/12785—Group IIB metal-base component
    • Y10T428/12792—Zn-base component
    • Y10T428/12799—Next to Fe-base component [e.g., galvanized]

Definitions

  • the present disclosure relates to a zinc alloy plated steel sheet having high bending workability and a method for manufacturing the zinc alloy plated steel sheet.
  • a zinc plating method for suppressing the corrosion of iron by cathodic protection has high anti-corrosion efficiency and economic feasibility, and thus has been widely used in manufacturing steel materials having high corrosion resistance.
  • hot-dip zinc plated steel sheets manufactured by dipping a steel material into molten zinc to form a plating layer, are obtainable through simple manufacturing processes and are relatively inexpensive, as compared to electro-zinc plated steel sheets, and thus, demand therefor has increased in a wide range of industries, such as the automotive industry, the home appliance industry, and the construction industry.
  • the zinc alloy plated steel sheet includes large amounts of Zn—Al—Mg-based intermetallic compounds in a plating layer thereof as a result of thermodynamic reaction between zinc (Zn), aluminum (Al), and magnesium (Mg), and such intermetallic compounds may cause cracks in the plating layer during a bending process because of high hardness of the intermetallic compounds, thereby lowering the bending workability of the zinc alloy plated steel sheet.
  • aspects of the present disclosure may provide a zinc alloy plated steel sheet having high bending workability and a method for manufacturing the zinc alloy plated steel sheet.
  • a zinc alloy plated steel sheet may include a base steel sheet and a zinc alloy plating layer, wherein the zinc alloy plating layer may include a Zn single phase structure as a microstructure and a Zn—Al—Mg-based intermetallic compound, and the Zn single phase structure may have a degree (f) of (0001) preferred orientation, expressed by Formula 1 below, within a range of 50% or greater,
  • I total refers to an integral of all diffraction peaks of the Zn single phase structure when an X-ray diffraction pattern is measured within a range of 2 theta from 10° to 100° using a Cu-K ⁇ source
  • I basal refers to an integral of diffraction peaks of the Zn single phase structure relating to a basal plane.
  • a method for manufacturing a zinc alloy plated steel sheet may include: preparing a zinc alloy plating bath including magnesium (Mg) and aluminum (Al); obtaining a zinc alloy plated steel sheet by dipping a base steel sheet into the zinc alloy plating bath to plate the base steel sheet; wiping the zinc alloy plated steel sheet with gas to adjust a plating weight; and after adjusting the plating weight of the zinc alloy plated steel sheet, cooling the zinc alloy plated steel sheet by spraying droplets of water or an aqueous solution onto the zinc alloy plated steel sheet and then using air, wherein when the droplets are sprayed, a droplet spray start temperature ranges from 405° C. to 425° C., a droplet spray stop temperature ranges from 380° C. to 400° C.
  • an embodiment of the present disclosure provides a zinc alloy plated steel sheet having high bending workability as well as high corrosion resistance.
  • the zinc alloy plated steel sheet of the embodiment has high surface quality.
  • the zinc alloy plated steel sheet of the embodiment has high scratch resistance.
  • FIG. 1 is views illustrating results of (a) an observation of a surface microstructure of Inventive Sample 1 and (b) an observation of a surface microstructure of Comparative Sample 5.
  • FIG. 2 is views illustrating results of (a) an observation of a cross-sectional microstructure of Inventive Sample 1 and (b) an observation of a cross-sectional microstructure of Comparative Sample 5.
  • FIG. 3 is a view illustrating results of X-ray diffractometer (XRD) analysis of Inventive Sample 1.
  • the zinc alloy plated steel sheet includes a base steel sheet and a zinc alloy plating layer.
  • the base steel sheet is not limited to a particular type.
  • a hot-rolled steel sheet or a cold-rolled steel sheet commonly used as a base steel sheet of a zinc alloy plated steel sheet may be used.
  • hot-rolled steel sheets have a large amount of surface oxide scale that lowers plating adhesion and thus plating quality, and thus a hot-rolled steel sheet from which oxide scale has been previously removed using an acid solution may be used as the base steel sheet.
  • the zinc alloy plating layer may be formed on one or each side of the base steel sheet.
  • the zinc alloy plating layer may include, by wt %, aluminum (Al): 0.5% to 3%, magnesium (Mg): 0.5% to 3%, and the balance of zinc (Zn) and inevitable impurities.
  • magnesium (Mg) reacts with zinc (Zn) and aluminum (Al) and forms a Zn—Al—Mg-based intermetallic compound, thereby functioning as a key element improving the corrosion resistance of the zinc alloy plated steel sheet. If the content of magnesium (Mg) is excessively low, the Zn—Al—Mg-based intermetallic compound is not present in sufficient amounts in the microstructure of the zinc alloy plating layer, and thus corrosion resistance may not be sufficiently improved. Therefore, the amount of magnesium (Mg) in the zinc alloy plating layer may be 0.5 wt % or greater, preferably 1.0 wt % or greater.
  • the amount of magnesium (Mg) in the zinc alloy plating layer may be 3 wt % or less, preferably 2.9 wt % or less.
  • Aluminum (Al) suppresses the formation of Mg oxide dross and reacts with zinc (Zn) and magnesium (Mg) to form the Zn—Al—Mg-based intermetallic compound in the zinc alloy plating layer, thereby functioning as a key element improving the corrosion resistance of the zinc alloy plated steel sheet. If the content of aluminum (Al) is excessively low, the formation of Mg dross is not sufficiently suppressed, and the Zn—Al—Mg-based intermetallic compound is not present in sufficient amounts in the microstructure of the zinc alloy plating layer, which may result in insufficient improvements in corrosion resistance.
  • the amount of aluminum (Al) in the zinc alloy plating layer may be 0.5 wt % or greater, preferably 0.6 wt % or greater.
  • the content of aluminum (Al) is excessively high, the effect of improving corrosion resistance is saturated, and the durability of plating equipment may be negatively affected because of a high plating bath temperature.
  • the Zn—Al—Mg-based intermetallic compound having high harness may be formed in excessively large amounts in the microstructure of the zinc alloy plating layer, and thus bending workability may be lowered. Therefore, the amount of aluminum (Al) in the zinc alloy plating layer may be 3 wt % or less, preferably 2.6 wt % or less.
  • the contents of magnesium (Mg) and aluminum (Al) in the zinc alloy plating layer may satisfy the following Formula 2. If [Mg]/[Al] is 1.0 or less, scratch resistance may deteriorate, and if [Mg]/[Al] is greater than 4.0, Mg-based dross may be formed in large amounts in a hot-dip plating bath to lower workability.
  • the zinc alloy plating layer may include a Zn single phase structure as a microstructure and the Zn—Al—Mg-based intermetallic compound.
  • the Zn—Al—Mg-based intermetallic compound is not limited to a particular type.
  • the Zn—Al—Mg-based intermetallic compound may include at least one selected from the group consisting of a Zn/Al/MgZn 2 ternary eutectic structure, a Zn/MgZn 2 binary eutectic structure, a Zn/Al binary eutectic structure, and an MgZn 2 single phase structure.
  • the inventors have conducted in-depth research into improving the bending workability of zinc alloy plated steel sheets and found that if a Zn single phase structure having a hexagonal close packing (HCP) structure is grown in a (0001) orientation in the microstructure of the zinc alloy plating layer, ductility increases owing to easy slippage, and thus cracks are markedly reduced in a bending process.
  • HCP hexagonal close packing
  • the degree (f) of (0001) preferred orientation may preferably be adjusted to be 50% or greater, more preferably 60% or greater.
  • I total refers to the integral of all diffraction peaks of the Zn single phase structure when an X-ray diffraction pattern is measured within the range of 2 theta from 10° to 100° using a Cu-K ⁇ source
  • I basal refers to the integral of diffraction peaks of the Zn single phase structure relating to a basal plane.
  • the inventors have found that if the Zn single phase structure coarsely formed in the zinc alloy plating layer is refined in size, it is also helpful to reduce cracking during a bending process.
  • the average grain diameter of the Zn single phase structure may be preferably adjusted to be 15 ⁇ m or less, more preferably 12 ⁇ m or less, and even more preferably 10 ⁇ m or less.
  • the “average grain diameter” of the Zn single phase structure refers to the average of equivalent circular diameters of the Zn single phase structure measured by observing a thicknesswise cross-section of the zinc alloy plating layer.
  • the zinc alloy plated steel sheet of the present disclosure has high corrosion resistance and bending workability as well.
  • the zinc alloy plated steel sheet of the present disclosure may have a good appearance.
  • the number of black spots per unit area may be equal to or less than 0.1/cm 2 on the surface of the zinc alloy plated steel sheet.
  • the area fraction of the Zn single phase structure may preferably be 40% or less (excluding 0%) on the surface of the zinc alloy plating layer. That is, the appearance of the zinc alloy plated steel sheet may be improved by maximizing the fraction of the Zn—Al—Mg-based intermetallic compound present on the surface of the zinc alloy plating layer.
  • the zinc alloy plated steel sheet of the present disclosure may also have high scratch resistance.
  • the sum of the area fractions of the Zn/MgZn 2 binary eutectic structure and the Zn/Al/MgZn 2 ternary eutectic structure may be 50% or greater (excluding 100%), and the area fraction of the MgZn 2 single phase structure may be 10% or less (including 0%).
  • the MgZn 2 single phase structure has high hardness and thus causes cracks during a machining process, and thus the area fraction of the MgZn 2 single phase structure may be adjusted to be as low as possible.
  • the zinc alloy plated steel sheet of the present disclosure may be manufactured by various methods without limitation. However, for example, when the zinc alloy plating layer solidifies from a molten state, the zinc alloy plating layer may be cooled by spraying droplets thereon and then cooled with air to obtain the above-described degree of preferred orientation and average grain diameter.
  • droplets may be sprayed by a charge spray method to attach the droplets by electrostatic attraction between the droplets and the zinc alloy plated steel sheet.
  • This charge spray method may be helpful in forming fine, uniform droplets and reducing the amount of droplets colliding with and bouncing off the zinc alloy plated steel sheet after being sprayed on the zinc alloy plated steel sheet, thereby facilitating rapid cooling of the zinc alloy plating layer from the molten state and having a positive effect on the growth of the Zn single phase structure in the (0001) orientation and refinement of the Zn single phase structure.
  • the droplets may be droplets of a phosphate aqueous solution capable of rapidly cooling the zinc alloy plating layer from the molten state through an endothermic reaction and thus effective in growing the Zn single phase structure in the (0001) orientation and refining the Zn single phase structure.
  • the phosphate aqueous solution may include an aqueous solution of ammonium hydrogen phosphate ((NH 4 ) 2 HPO 4 ), an aqueous solution of sodium ammonium hydrogen phosphate (NaNH 4 HPO 4 ), an aqueous solution of zinc dihydrogen phosphate (Zn(H 2 PO 4 ) 2 ), and an aqueous solution of calcium phosphate (Ca 3 (PO 4 ) 2 ).
  • the content of the phosphate aqueous solution may be 1 wt % to 3 wt %. If the content of the phosphate aqueous solution is less than 1 wt %, the effect of the phosphate aqueous solution may not be sufficient. If the content of the phosphate aqueous solution is greater than 3 wt %, the effect of the phosphate aqueous solution is saturated, and nozzle clogging may occur in a continuous production process, lowering productivity.
  • droplets when the droplets may be sprayed at a droplet spray start temperature of 405° C. to 425° C., and more preferably 410° C. to 420° C.
  • droplet spray start temperature refers to a surface temperature of the zinc alloy plated steel sheet at the start time of droplet spraying. If the droplet spray start temperature is less than 405° C., solidification of the Zn single phase structure may have already started, and thus black spots may be formed on the surface of the zinc alloy plated steel sheet. Conversely, if the droplet spray start temperature is greater than 425° C., droplets may not effectively undergo an endothermic reaction, and thus it may be difficult to obtain an intended structure.
  • the droplets may be sprayed at a droplet spray stop temperature of 380° C. to 400° C., and more preferably 390° C. to 400° C.
  • the term “droplet spray stop temperature” refers to a surface temperature of the zinc alloy plated steel sheet at a point in time at which spraying of droplets stops. If the droplet spray stop temperature is greater than 400° C., an endothermic reaction by the droplets may occur ineffectively, and thus it may be difficult to obtain an intended structure.
  • a Mg 2 Zn 11 phase may be formed due to over cooling while the Zn/MgZn 2 binary eutectic phase and the Zn/Al/MgZn 2 ternary phase start to solidify, and thus many black spots may be formed, decreasing the degree of (0001) preferred orientation of the Zn single phase structure.
  • the difference between the droplet spray start temperature and the droplet spray stop temperature may be 15° C. or greater. If the difference is less than 15° C., the droplets may not undergo an effective endothermic reaction, and thus it may be difficult to obtain an intended structure.
  • the droplets may be sprayed in an amount of 50 g/m 2 to 100 g/m 2 . If the spraying amount of the droplets is less than 50 g/m 2 , the effect of the droplets may be insufficient, and if the spraying amount of the droplets is greater than 100 g/m 2 , the effect of the droplets may be saturated.
  • Low carbon cold-rolled steel sheets each having a thickness of 0.8 mm, a width of 100 mm, and a length of 200 mm were prepared as base steel sheets for plating test samples, and then foreign substances such as rolling oil were removed from the surfaces of the base steel sheets by dipping the base steel sheets into acetone and washing the base steel sheets with ultrasonic waves. Thereafter, a 750° C. reducing atmosphere heat treatment commonly performed to guarantee mechanical characteristics of steel sheets in the hot-dipping plating field was performed on the base steel sheets, and then the base steel sheets were dipped into plating baths (bath temperature: 460° C.) having compositions shown in Table 1 below to fabricate zinc alloy plated steel sheets.
  • bath temperature bath temperature: 460° C.
  • Comparative Sample 5 was prepared by performing a gas wiping process on a zinc alloy plated steel sheet fabricated using the same plating bath as that used to fabricate Inventive Sample 1 to adjust a plating weight to be 70 g/m 2 on each side, and then cooling the zinc alloy plated steel sheet using a general cooling device at an average cooling rate of 12° C./sec until the plating layer of the zinc alloy plated steel sheet was completely solidified (at about 300° C. or less).
  • the microstructures of the fabricated zinc alloy plated steel sheets were observed using an FE-SEM (SUPRA-55VP, Zeiss) as illustrated in FIGS. 1 and 2 , and the average grain diameter of a Zn single phase structure of each of the zinc alloy plated steel sheets was measured as shown in Table 2 below.
  • I total refers to the integral of all diffraction peaks of the Zn single phase structure when an X-ray diffraction pattern was measured within the range of 2 theta from 10° to 100° using a Cu-K ⁇ source
  • I basal refers to the integral of diffraction peaks of the Zn single phase structure relating to a basal plane.
  • Corrosion resistance was evaluated as follows. A salt spray test (based on KS-C-0223) was performed on each of the zinc alloy plated steel sheets to facilitate corrosion, and then the time taken until the area fraction of red rust on the surface of each plating layer was 5% was measured.
  • 3T bending was performed on each of the zinc alloy plated steel sheets, and a 1-mm length of the apex of each bent portion was observed using an SEM to measure the area fraction of bending cracks using an image analysis system.
  • Comparative Samples 1 to 5 had high corrosion resistance, Comparative Samples 1 to 5 had poor bending workability because the (f) values thereof were less than 50%.
  • FIG. 1 is views illustrating results of (a) an observation of a surface microstructure of Inventive Sample 1 of the present disclosure and (b) an observation of a surface microstructure of Comparative Sample 5
  • FIG. 2 is views illustrating results of (a) an observation of a cross-sectional microstructure of Inventive Sample 1 of the present disclosure and (b) an observation of a cross-sectional microstructure of Comparative Sample 5.
  • FIG. 3 is a view illustrating results of X-ray diffractometer (XRD) analysis of Inventive Sample 1.
  • XRD X-ray diffractometer
  • Low carbon cold-rolled steel sheets each having a thickness of 0.8 mm, a width of 100 mm, and a length of 200 mm were prepared as base steel sheets for plating test samples, and then foreign substances such as rolling oil were removed from the surfaces of the base steel sheets by dipping the base steel sheets into acetone and washing the base steel sheets with ultrasonic waves. Thereafter, a 750° C. reducing atmosphere heat treatment commonly performed to guarantee mechanical characteristics of steel sheets in the hot-dipping plating field was performed on the base steel sheets, and then the base steel sheets were dipped into plating baths having compositions shown in Table 3 below to fabricate zinc alloy plated steel sheets. Thereafter, each of the zinc alloy plated steel sheets was wiped with gas to adjust a plating weight to be 70 g/m 2 on each side. Then, the zinc alloy plated steel sheets were cooled under the same conditions as Inventive Sample 1 of Example 1.
  • a friction test (linear friction test) was performed by rubbing the surface of each of the zinc alloy plated steel sheets 20 times with a tool head at a constant pressure.
  • a target load was 333.3 kgf
  • a pressure was 3.736 MPa
  • the tool head traveled 200 mm per rub
  • the speed of the tool head was 20 mm/s.
  • each of the zinc alloy plated steel sheets was inserted into a salt spray tester, and the time taken until the occurrence of red rust was measured according to international standard ASTM B117-11. In that time, a 5% salt solution (35° C., pH 6.8) was sprayed at a rate of 2 ml/80 cm 2 per hour.
  • a 5% salt solution 35° C., pH 6.8 was sprayed at a rate of 2 ml/80 cm 2 per hour.
  • each of Comparative Samples A, B, D, and E had poor appearance because the area fraction of a Zn single phase structure present on the surface of a plating layer was excessively high, and each of Comparative Samples A to G had poor scratch resistance because the area fractions of a Zn/MgZn 2 binary eutectic structure and a Zn/Al/MgZn 2 ternary eutectic structure are excessively low.

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  • Engineering & Computer Science (AREA)
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  • Organic Chemistry (AREA)
  • Coating With Molten Metal (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)
  • Laminated Bodies (AREA)
US15/770,615 2015-10-26 2016-10-26 Zinc alloy plated steel sheet having excellent bending workability and manufacturing method therefor Abandoned US20180320260A1 (en)

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US11168389B2 (en) 2015-12-24 2021-11-09 Posco Plated steel sheet having fine and even plating structure
US11473174B2 (en) * 2017-01-16 2022-10-18 Nippon Steel Corporation Coated steel product
US11725259B2 (en) 2019-04-19 2023-08-15 Nippon Steel Corporation Plated steel sheet

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US11834747B2 (en) * 2019-06-26 2023-12-05 Posco Co., Ltd Plated steel wire and manufacturing method for the same
EP4022102A1 (en) 2019-08-30 2022-07-06 Rijksuniversiteit Groningen Characterization method of formability properties of zinc alloy coating on a metal substrate
CN111155044B (zh) * 2019-12-13 2021-09-21 首钢集团有限公司 一种提高锌铝镁镀层钢表面质量的方法、锌铝镁镀层
WO2023238940A1 (ja) * 2022-06-10 2023-12-14 日本製鉄株式会社 Ｚｎ－Ａｌ－Ｍｇ系溶融めっき鋼板

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JP3179401B2 (ja) * 1996-12-13 2001-06-25 日新製鋼株式会社 耐食性および表面外観の良好な溶融Ｚｎ−Ａｌ−Ｍｇめっき鋼板およびその製造法
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BRPI0519664A2 (pt) * 2004-12-28 2009-03-03 Posco chapa de aÇo galvanizada sem flores de zinco, seu mÉtodo de produÇço e equipamento usado para tal produÇço
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11168389B2 (en) 2015-12-24 2021-11-09 Posco Plated steel sheet having fine and even plating structure
US11473174B2 (en) * 2017-01-16 2022-10-18 Nippon Steel Corporation Coated steel product
US11725259B2 (en) 2019-04-19 2023-08-15 Nippon Steel Corporation Plated steel sheet

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CN108350555A (zh) 2018-07-31
EP3369838A1 (en) 2018-09-05
KR20170049422A (ko) 2017-05-10
JP2018532889A (ja) 2018-11-08
EP3369838A4 (en) 2018-09-05
JP6983153B2 (ja) 2021-12-17
EP3369838B1 (en) 2019-08-21
KR101819381B1 (ko) 2018-01-18

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