EP4411016A1 - Tôle d'acier plaquée présentant d'excellentes propriétés de résistance à la corrosion et de soudabilité, et son procédé de fabrication - Google Patents

Tôle d'acier plaquée présentant d'excellentes propriétés de résistance à la corrosion et de soudabilité, et son procédé de fabrication Download PDF

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Publication number
EP4411016A1
EP4411016A1 EP22876842.0A EP22876842A EP4411016A1 EP 4411016 A1 EP4411016 A1 EP 4411016A1 EP 22876842 A EP22876842 A EP 22876842A EP 4411016 A1 EP4411016 A1 EP 4411016A1
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EP
European Patent Office
Prior art keywords
steel sheet
plated layer
content
plated
weight
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP22876842.0A
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German (de)
English (en)
Inventor
Sung-Joo Kim
Tae-Chul Kim
Myung-Soo Kim
Bong-Hwan YOO
Yong-Kyun Cho
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Posco Holdings Inc
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Posco Co Ltd
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Filing date
Publication date
Application filed by Posco Co Ltd filed Critical Posco Co Ltd
Publication of EP4411016A1 publication Critical patent/EP4411016A1/fr
Pending legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
    • B24C1/00—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods
    • B24C1/10—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods for compacting surfaces, e.g. shot-peening
    • 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
    • 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
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • 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
    • 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
    • C23C2/26—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
    • C23C2/34—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

Definitions

  • the present disclosure relates to a high-corrosion resistance plated steel sheet having excellent corrosion resistance and weldability and a method for manufacturing the same.
  • a galvanized steel sheet When a galvanized steel sheet is exposed to a corrosive environment, a galvanized steel sheet may have sacrificial properties in which zinc, having a lower redox potential than that of iron, is corroded first, such that corrosion of a steel material may be prevented. Also, as zinc in a plated layer oxidizes, dense corrosion products may be formed on the surface of a steel material, thereby blocking the steel material from the oxidizing atmosphere and improving corrosion resistance of the steel material. Due to the advantageous properties, the application of a galvanized steel sheet has been increased to include steel sheets for construction materials, home appliances, and automobiles.
  • a Zn-Mg-Al-based galvanized alloy steel sheet may be often used by being painted or welded.
  • phosphatability required for painting pre-treatment may decrease due to Al-based oxide, such that painting adhesion may deteriorate.
  • pores may remain in a welded metal due to influence of Al vapor during arc welding, which may cause a decrease in strength of the welded zone.
  • a galvanized steel sheet after processing may be often provided on the periphery of products, but surface damage factors such as partial peeling due to paint adhesion deterioration and deformation of a welded zone due to welding pores may be added, such that surface quality may be poor, and accordingly, exterior quality may need to be improved.
  • An aspect of the present disclosure is to provide a plated steel sheet having excellent corrosion resistance and weldability and a method for manufacturing the same.
  • another aspect of the present disclosure is to provide a plated steel sheet having excellent corrosion resistance, weldability and phosphatability and a method for manufacturing the same.
  • An aspect of the present disclosure provides
  • [Zn] 1/10t represents a weight% content of Zn in a 1/10t position (t is a total thickness of the plated layer) in a thickness direction from a surface of the plated layer
  • [Zn] s represents a weight% content of Zn on a surface of the plated layer.
  • [Al] 1/10t represents a weight% content of Al in a 1/10t position (t is a total thickness of the plated layer) in a thickness direction from a surface of the plated layer
  • [Al] s represents a weight% content of Al on a surface of the plated layer.
  • Another aspect of the present disclosure provides
  • a plated steel sheet having excellent corrosion resistance and weldability and a method for manufacturing the same may be provided.
  • a plated steel sheet having excellent corrosion resistance, weldability and phosphatability and a method for manufacturing the same may be provided.
  • FIG. 1 is a diagram illustrating a component analysis profile using GDS for a plated steel sheet obtained in Embodiment 7.
  • Mg may be added to improve corrosion resistance.
  • floating dross may increase in a plating bath, such that the dross may need to be removed frequently, which may be problematic, and an upper limit of Mg content may be limited to 3%.
  • the technical attempts have been conducted, such as, by increasing the Al content simultaneously as the Mg content increases, Al oxide may be preferentially formed on the plating bath surface rather than Mg oxide, such that Mg oxide-based floating dross may be prevented, and the exterior of the product may be prevented from being easily darkened.
  • the present inventors conducted intensive studies to address the above-mentioned problems and to provide a plated steel sheet having excellent corrosion resistance and also excellent weldability and/or phosphatability.
  • the content change of each component e.g., Zn and Al, and further comprising Mg
  • t is a total thickness of the plated layer
  • the plated steel sheet according to the present disclosure may comprise a base steel sheet; and a Zn-Mg-Al-based plated layer provided on at least one surface of the base steel sheet.
  • the type of base steel sheet may not be particularly limited.
  • the base steel sheet may be implemented as an Fe-based base steel sheet used as a base steel sheet of general galvanized steel sheet, that is, a hot-rolled steel sheet or a cold-rolled steel sheet, but an embodiment thereof is not limited thereto.
  • the base steel sheet may be, for example, carbon steel, ultra-low carbon steel, or high manganese steel used as a material for construction, home appliances, and automobiles.
  • the base steel sheet may have a composition of, in weight%, C: more than 0% (more preferably, 0.001% or more) and 0.18% or less, Si: more than 0% (more preferably, 0.001% or more) and 1.5% or less, Mn: 0.01 to 2.7%, P: more than 0% (more preferably, 0.001% or more) and 0.07% or less, S: more than 0% (more preferably, 0.001% or more) and 0.015% or less, Al: more than 0% (more preferably, 0.001% or more) and 0.5% or less, Nb: more than 0% (more preferably, 0.001% or more) and 0.06% or less, Cr: more than 0% (more preferably, 0.001% or more) and 1.1% or less, Ti: more than 0% ( more preferably, 0.001% or more) and 0.06% or less, B: more than 0% (more preferably, 0.001% or more) and 0.03% or less and a balance of Fe and inevitable impurities.
  • At least one surface of the base steel sheet may be provided with a Zn-Mg-Al-based plated layer consisted of a Zn-Mg-Al-based alloy.
  • the plated layer may be formed on only one surface of the base steel sheet, or may be formed on both surfaces of the base steel sheet.
  • the Zn-Mg-Al-based plated layer may refer to a plated layer comprising Mg and Al and mainly comprising Zn (comprising more than 50% of Zn).
  • a thickness of the Zn-Mg-Al-based plated layer may be 9 to 100 ⁇ m, more preferably 20 to 90 um.
  • the thickness of the plated layer may excessively decrease locally due to errors resulting from the thickness deviation of the plated layer, such that corrosion resistance may deteriorate.
  • the thickness of the plated layer exceeds 100 ⁇ m, cooling of the molten plated layer may be delayed, a solidification defect such as a flow pattern, for example, may occur on the surface of the plated layer, and productivity of the steel sheet may decrease to solidify the plated layer.
  • an Fe-Al-based inhibition layer may be further comprised between the base steel sheet and the Zn-Mg-Al-based plated layer.
  • the Fe-Al-based inhibition layer may mainly comprise an intermetallic compound of Fe and Al (e.g., more than 60%), and examples of the intermetallic compound of Fe and Al may comprise FeAl, FeAl 3 , and Fe 2 Al 5 .
  • some components derived from the plated layer, such as Zn and Mg may be further comprised, for example, up to 40%.
  • the inhibition layer may be formed due to alloying by Fe and plating bath components diffused from the base steel sheet at an initial stage of plating.
  • the inhibition layer may improve adhesion between the base steel sheet and the plated layer, and may also prevent Fe diffusion from the base steel sheet to the plated layer.
  • the inhibition layer may be formed continuously between the base steel sheet and the Zn-Mg-Al-based plated layer, or may be formed discontinuously. In this case, other than the above-mentioned description, regarding the inhibition layer, a commonly known description in the relevant technical field may be applied.
  • a thickness of the inhibition layer may be 0.01 to 2.50 um.
  • the inhibition layer may assure corrosion resistance by preventing alloying, but as the layer is brittle, the layer may affect processability, and accordingly, a thickness thereof may be determined to be 2.50 ⁇ m or less.
  • the thickness may be 0.01 um or more.
  • an upper limit of the thickness of the inhibition layer may be 1.80 um.
  • a lower limit of the inhibition layer thickness may be 0.02 um.
  • the thickness of the inhibition layer may refer to a minimum thickness in the direction perpendicular to an interfacial surface of the base steel sheet.
  • the Zn-Mg-Al based plated layer may comprise, in weight%, Mg: 4.0 to 7.0%, Al: 8.2 to 19.5%, a balance of Zn and inevitable impurities.
  • Mg Mg: 4.0 to 7.0%
  • Al Al: 8.2 to 19.5%
  • a balance of Zn and inevitable impurities a balance of Zn and inevitable impurities.
  • Mg 4.0% or more and 7.0% or less
  • Mg may improve corrosion resistance of a plated steel material.
  • a Mg content in the plated layer may be controlled to 4.0% or more to assure desired excellent corrosion resistance.
  • the Mg content may be controlled to 7.0% or less.
  • a lower limit of the Mg content may be 4.7%, or an upper limit of the Mg content may be 6.0%.
  • Mg when Mg is added at 1% or more, the effect of improving corrosion resistance may be exhibited, but when Mg is added at 2% or more, floating dross may increase in a plating bath due to oxidation of Mg in the plating bath, such that it may be necessary to reduce dross. Due to this problem, in the prior art, by adding more than 1.0% of Mg in Zn-Mg-Al-based zinc alloy plating, corrosion resistance may be assured, and an upper limit of Mg content may be determined to be 3.0% for commercialization. However, as mentioned above, to further improve corrosion resistance, it may be necessary to increase the Mg content to 4% or more.
  • the plated layer comprises 4% or more of Mg
  • dross may occur due to oxidation of Mg in the plating bath, which may be problematic, such that it may be necessary to add 8.2% or more of Al.
  • Al is added excessively to suppress dross, a melting point of the plating bath may increase and an operating temperature may thus increase excessively, such that problems caused by high-temperature work, such as erosion of the plating bath structure and deterioration of the steel material, may occur.
  • Al content in the plating bath when the Al content in the plating bath is excessive, Al may react with Fe of base iron and may not contribute to the formation of the Fe-Al inhibition layer, and the reaction between Al and Zn may occur rapidly, such that a lump-shaped outburst phase may be excessively formed, and corrosion resistance may actually deteriorate. Accordingly, it may be preferable to control an upper limit of Al content in the plated layer to 19.5%. Meanwhile, more preferably, in terms of maximizing the above-mentioned effect, a lower limit of the Al content may be 11.0%, or an upper limit of the Al content may be 18.0%.
  • Inevitable impurities may comprise components unintentionally mixed in a process of manufacturing general hot-dip galvanized steel sheet, and a person skilled in the relevant technical field may easily understand the addition.
  • the plated layer may satisfy relational expressions 1 and 2 below. ⁇ 10.0 ⁇ Zn 1 / 10 t ⁇ Zn s ⁇ ⁇ 5.0
  • [Zn] 1/10t represents a weight% content of Zn in a 1/10t position (t is a total thickness of the plated layer) in a thickness direction from a surface of the plated layer
  • [Zn] s represents a weight% content of Zn on a surface of the plated layer.
  • [Al] 1/10t represents a weight% content of Al in a 1/10t position (t is a total thickness of the plated layer) in a thickness direction from a surface of the plated layer
  • [Al] s represents a weight% content of Al on a surface of the plated layer.
  • the present inventors conducted a thorough study to assure further improved corrosion resistance as compared to the prior art and also to assure weldability and/or phosphatability. As a result, it was found that, excluding the effect of oxidation on the plated layer, the content change of each component (e.g., Zn and Al, and further comprising Mg) in the surface layer region from the plated layer surface to the 1/10t position in a thickness direction (t is a total thickness of the plated layer) may be an important factor.
  • each component e.g., Zn and Al, and further comprising Mg
  • the Zn-Mg-Al-based plated layer may comprise a Zn single phase and a Zn-MgZn 2 -Al-based ternary eutectic phase, which are common phases in a high-corrosion resistance plated steel sheet.
  • the amount of Zn single phase and Zn-MgZn 2 -Al ternary eutectic phase may be increased in the entire plated layer, and as the Al and Mg content in the plated layer increases, the amount of MgZn 2 phase and Al single phase may increase.
  • the Al content may also need to increase simultaneously to suppress dross, such that the Al single phase may also be present. Accordingly, through repeated research, the present inventors have determined that, by suppressing nucleation and growth of the aforementioned MgZn 2 phase and Al single phase on the surface of the plated layer and promoting the same in the plated layer, distribution of Zn single phase, Al-Zn binary eutectic phase and Zn-MgZn 2 -Al ternary eutectic phase may be increased on the plated layer surface, and a plated layer surface having a high Zn component content and also a low Al component content may be formed.
  • the present inventors confirmed that, while assuring the aforementioned corrosion resistance, the region directly affecting weldability and phosphatability may be a surface layer region from the plated layer surface to the 1/10t position in the thickness direction. Accordingly, it was found that, by controlling a change in Zn content and a change in Al content in the surface region of the plated layer to satisfy the above-mentioned relational expressions 1 and 2, a plated steel sheet having excellent weldability and/or phosphatability and also excellent corrosion resistance may be effectively obtained.
  • a lower limit of the [Zn] 1/10t - [Zn] s value defined in relational expression 1 above may be -9.9, or an upper limit of the [Zn] 1/10t - [Zn] s value may be - 5.3 (most preferably, -7.0).
  • a lower limit of the [Al] 1/10t - [Al] s value defined in relational expression 2 may be +6.4, or an upper limit of the [Al] 1/10t - [Al] s value may be +11.1.
  • the present inventors conducted intensive studies to further improve corrosion resistance and, optionally, it was further found that, by controlling a profile of Mg content in the thickness direction to further satisfy relational expression 3 below, corrosion was carried out uniformly in the thickness direction, which has the effect of improving corrosion resistance to a higher level.
  • [Mg] 1/10t represents a weight% content of Mg in a 1/10t position (t is a total thickness of the plated layer) in a thickness direction from a surface of the plated layer
  • [Mg] s represents a weight% content of Mg on a surface of the plated layer.
  • a potential of MgZn2 may be -1.2V on hydrogen reduction potential, and a potential of Al is -0.7V on hydrogen reduction potential, such that a relatively large potential difference may be assured, and accordingly, the potentials may act as an anode and a cathode, respectively, and may form a galvanic cell between microstructures of the adjacent MgZn 2 phase and the Al single phase.
  • a lower limit of the [Mg] 1/10t - [Mg] s value defined in relational expression 3 above may be -0.8, or an upper limit of the [Mg] 1/10t - [Mg] s value may be +0.8.
  • the method of measuring the content of each component in the 1/10t position defined in the above-mentioned relational expressions 1 to 3 and the content of each component on the surface of the plated layer may not be particularly limited, and for example, the contents may be measured as below.
  • the plated steel material may be cut in the vertical direction, and the distribution of content of each component such as Zn, Al, Mg and Fe in the cross-section of the plated layer may be measured using a glow discharge optical emission spectrometry (GDS).
  • GDS glow discharge optical emission spectrometry
  • the region up to 0.1 um in the thickness direction from the outermost surface of the plated layer may be excluded in the present disclosure.
  • the above-mentioned 'surface of the plated layer' may refer to a point which may be 0.1 um position from an outermost surface of the plated layer in the thickness direction, excluding the region affected by oxidation.
  • a content of each component on the surface of the plated layer defined in the above relational expressions 1 to 3 may be defined as a content of each component (Zn, Al and Mg) in a position of 0.1 um from an outermost surface of the plated layer.
  • a distance from the plated layer surface to a position in which the Zn and Fe contents match each other may be defined as t with respect to a profile of each component measured using a GDS. Accordingly, the 1/10t position for the total thickness t of the plated layer may be defined, such that the content of each component (Zn, Al and Mg) measured by GDS at the 1/10t point may be measured.
  • the value of t up to a position in which the contents of Zn and Fe match each other may be about 34 um.
  • the 1/10t position may refer to a point about 3.4 um from the plated layer surface, and accordingly, by measuring the weight% content of each component at a point about 3.4 um from the plated layer surface, the values of [Zn] 1/10t , [Al] 1/10t , and [Mg] 1/10t may be measured.
  • the weight% content of Mg in the 2/3t position in the thickness direction from the surface of the plated layer may be in the range of ⁇ 0.5wt% based on an average weight% content of Mg in the plated layer. By satisfying this condition, corrosion may be carried out uniformly in the thickness direction, such that corrosion resistance may further improve.
  • the weight% content of Mg in the 2/3t position in the thickness direction from the surface of the plated layer may satisfy a ⁇ 0.3wt% range based on an average weight% content of Mg in the plated layer.
  • the method of measuring the weight% average content of Mg in the plated layer is not particularly limited.
  • the Mg content at each point may be measured every 0.5 um up to the shortest distance t, and an average value calculated therefrom may be obtained.
  • the Mg content in the 2/3t position may be obtained based on the previously defined t.
  • an area ratio of the Al single phase having a Zn solid-solution rate of 27 atomic% or more on the surface of the plated layer may be 2.0 to 10.1%.
  • the area ratio of the Al single phase having a Zn solid-solution rate of 27 atomic% or more is less than 2.0% or more than 10.0%, one or more properties of weldability and phosphatability may be deteriorated.
  • a lower limit of the area ratio of the Al single phase on which the Zn solid-solution rate is 27 atomic% or more may be 2.2%, or an upper limit of the area ratio of the Al single phase having the Zn solid-solution rate of 27 atomic% or more may be 4.0%.
  • the Al single phase may refer to a phase mainly formed of Al, regardless of the Zn solid-solution rate, and may refer to a phase in which a balance of Al is comprised, excluding impurities such as dissolved Zn and inevitably comprised Mg.
  • a balance of Al is comprised, excluding impurities such as dissolved Zn and inevitably comprised Mg.
  • the Al single phase present on the surface of the plated layer, an Al single phase having a low Zn solid-solution rate of less than 27%, and an Al single phase having a high Zn solid-solution rate of more than 27% may be present.
  • the area ratio of the Al single phase having a Zn solid-solution rate of 27% or more may be controlled low, and may be comprised 2.0 area% or more, which may be an effective factor in reducing Al oxide generated on the surface of the plated layer, which adversely affects weldability and phosphatability.
  • the method of measuring the area ratio of the Al single phase having a Zn solid-solution rate of 27 atomic% or more on the surface of the plated layer is not particularly limited.
  • images derived under scanning electron microscope (SEM) measurement conditions may be analyzed using an automatic image generation software based on the super-pixel algorithm of microstructure phase analysis software (RISA) of the Research Institute of Industrial Science and Technology (RIST).
  • RISA microstructure phase analysis software
  • the superpixel algorithm may be a mechanism of dividing the entire image into thousands to tens of thousands of regions (superpixels) and measuring similarity by comparing superpixels with similar patterns or features, calculating a histogram of the brightness values of a pixel, and automatically selecting superpixels when the similarity is greater than a predefined threshold.
  • a predefined threshold as for a boundary of the Al single phase in the image derived by SEM, by predefining each phase based on the Zn solid-solution rate of 27 atomic% employed in the Al single-phase organization using an EDS, histogramming and structure differentiation of brightness values on soft images may be possible.
  • the technical idea of the above-mentioned RISA may be indicated in Korean Laid-Open Patent Publication No. 2019-0078331 .
  • preparing a base steel sheet may be further comprised, and the type of the base steel sheet is not particularly limited.
  • a Fe-based base steel sheet used as the base steel sheet of the general hot-dip galvanized steel sheet may be a hot-rolled steel sheet or a cold-rolled steel sheet, but an embodiment thereof is not limited thereto.
  • the base steel sheet may be, for example, carbon steel, ultra-low carbon steel, or high manganese steel used as a material for construction, home appliances, and automobiles, but an embodiment thereof is not limited thereto. In this case, the above description may be applied to the base steel sheet.
  • a primary shot blasting treatment may be performed such that metal balls with a particle size of 0.6 to 1.0 mm are projected onto the surface of the base steel sheet at 400 to 1,200 kg/min.
  • the surface oxide of the base steel sheet before plating may be primarily removed, thereby ensuring the effect of reducing the effect of the oxide.
  • a secondary shot blasting treatment may be performed such that metal balls with a particle size of 0.2 to 0.5 mm are projected onto the surface of the base steel sheet at 400 to 1200 kg/min.
  • the base steel sheet having gone through the primary and secondary shot blasting treatment may comprise, by weight%, Mg: 4.0 to 7.0%, Al: 8.2 to 19.5%, and a balance of Zn and inevitable impurities, and may be immersed in the in a plating bath maintained at a temperature of Ts+20°C to Ts+80°C as compared to the solidification start temperature (Ts) in the phase diagram and may be hot-dip galvanized.
  • the description of the components of the plated layer described above may be applied.
  • a composite ingot comprising predetermined Zn, Al and Mg or a Zn-Mg or a Zn-Al ingot comprising individual components may be used.
  • the ingot may be further melted and supplied.
  • the ingot may be dissolved by being directly immersed in a plating bath, or the ingot may be melted in a separate pot and the molten metal may be added to the plating bath.
  • the temperature of the plating bath may be maintained at a temperature 20 to 80°C higher than the solidification start temperature (Ts) on the phase diagram (Ts+20°C to Ts+80°C) .
  • the solidification start temperature in the equilibrium phase diagram may be in the range of 390 to 460°C, or the temperature of the plating bath may be maintained in the range of 440 to 520°C.
  • the temperature of the plating bath increases, fluidity may be assured in the plating bath and a uniform composition may be formed, and the amount of floating dross may be reduced.
  • the temperature of the plating bath is less than Ts+20°C, the dissolution of the ingot may be extremely slow and viscosity of the plating bath may be relatively high, it may be difficult to assure excellent surface quality of the plated layer. Meanwhile, when the temperature of the plating bath exceeds Ts+80°C, ash defects due to Zn evaporation may occur on the plating surface.
  • the hot-dip galvanized steel sheet may be cooled using an inert gas at an average cooling rate of 2 to 8°C/s from the solidification start temperature to the solidification end temperature with reference to the surface temperature.
  • the slow cooling may contribute to promoting nucleation and growth in the plated layer rather than on the surface of the plated layer. Accordingly, when the above-mentioned average cooling rate is less than 2°C/s, the MgZn 2 structure may be formed too coarsely on the surface and the entire plated layer may become brittle, which may increase cracks and may be disadvantageous in assuring uniform corrosion resistance and processability.
  • the change from the liquid phase to the solid phase may occur too rapidly during the hot-dip plating process, and uneven phases may be formed locally on the surface of the plated layer, such that color deviation in the width direction and corrosion resistance of the plated steel sheet may be reduced.
  • performing pre-temper rolling by applying a roll reduction of 100 to 400 tons to the surface of the base steel sheet having gone through the shot blasting treatment using a dull roll having a surface roughness Ra of 1.8 to 2.8 um may be further comprised.
  • the present inventors found that, by performing a pre-temper rolling (SPM) treatment using a dull roll satisfying the above-mentioned conditions, the surface shape of the base steel sheet may be controlled irregularly, and accordingly that the effect of maximizing the creation site of solidification nuclei in the plated layer may be obtained by the subsequent plating process.
  • SPM pre-temper rolling
  • the surface roughness Ra of the dull roll is less than 1.8 um, there may be a problem of promoting nucleation in the surface layer of the plated layer rather than nucleation in the plated layer. Meanwhile, when the surface roughness Ra of the dull roll exceeds 2.8 um, excessive dents may occur in the base steel sheet, such that the thickness of the molten plated layer formed by the subsequent plating process may become uneven in the width direction.
  • the shape control effect of the base steel sheet may be low, such that it may be difficult to expect the effect of promoting solidification nucleation in the plated layer, and when the roll reduction of the dull roll exceeds 400 tons, there may be a risk of inducing C bending of the base steel sheet, and it may be difficult to expect the effect of contributing to uniform formation of the plated layer in the thickness direction.
  • a plated steel sheet having excellent corrosion resistance and also weldability and/or phosphatability may be effectively provided.
  • Embodim ent 1 1.0 1600 500 0.2 1400 700 Bright* 0.6 200 Embodim ent 2 0.6 1300 700 0.4 1200 600 Bright 0.2 300 Embodim ent 3 1.0 1500 1000 0.2 1300 800 Bright 0.4 100 Embodim ent 4 0.8 1330 1000 0.2 1200 800 Dull* 2.0 50 Embodim ent 5 0.8 1900 900 0.4 1700 700 Dull 2.0 600 Embodim ent 6 1.0 1500 600 0.2 1900 1000 Unused - - Embodim ent 7 1.0 2000 800 0.2 1200 700 Dull 2.8 350 Embodim ent 1 1.0 1600 500 0.2 1400 700 Bright* 0.6 200 Embodim ent 2 0.6 1300 700 0.4 1200 600 Bright 0.2 300 Embodim ent 3 1.0 1500 1000 0.2 1300 800 Bright 0.4 100 Embodim ent 4 0.8 1330 1000 0.2 1200 800 Dull* 2.0 50 Embodim ent 5 0.8 1900 900 0.4 1700 700 Dull 2.0 600 Embodim ent 6 1.0 1500 600 0.2 1900 1000
  • a sample of the plated steel sheet described above was manufactured, the plated layer was dissolved in a hydrochloric acid solution, the dissolved liquid was analyzed by wet analysis (ICP) to measure the composition of the plated layer, and was listed in Table 3 below (however, a balance of Zn and inevitable impurities were comprised).
  • ICP wet analysis
  • a cross-sectional sample cut in the thickness direction of the steel sheet (in the direction perpendicular to the rolling direction) was manufactured such that the plated layer and the base iron interfacial surface were able to be observed, was imaged using a scanning electron microscope (SEM), and it was confirmed that a Fe-Al-based inhibition layer having a thickness of 0.02 ⁇ m was formed between the base steel sheet and the Zn-Mg-Al-based plated layer.
  • SEM scanning electron microscope
  • component analysis was performed from the surface of the plated layer in the thickness direction using a GDS measurement device, the content in the 1/10t position for each component of Zn, Al and Mg was measured, and excluding the region up to 0.1 um from the surface, the content at the surface at the 0.1 um point was measured to exclude the influence of oxidation, and was listed in Table 3 below. [Table 3] No.
  • the weight% content of Mg was measured in a 2/3t position in the thickness direction from the surface of the plated layer in the same manner as described above in this specification.
  • the average weight% content of Mg in the plated layer was also measured in the same manner as described above in this specification.
  • Corrosion resistance was evaluated according to the following criteria using a salt spray tester and a test method in accordance with ISO14993.
  • the steel sheet went through the processes in the order of degreasing - washing - surface adjustment - phosphate treatment, the free acidity in the phosphate solution was 0.7 to 0.9, and total acidity was 19 to 21, and accelerator was 4 to 4.5. Also, using a scanning electron microscope (SEM), three random points on the surface of the steel sheet were observed at a magnification of 1,000 times, and 20 phosphate particles were selected within one observation in order of increasing longitudinal size of phosphate particles, an average thereof was obtained, an average value of the three points was calculated, and phosphatability was evaluated according to the values as below.
  • SEM scanning electron microscope
  • the amount of spatter generation, which affects welding workability, and a pore rate, which affects tensile strength of the weld zone were evaluated.
  • gas metal arc (GMA) welding was performed under the conditions of gas CO 2 , welding material KC-28 solid wire, current 150A, voltage 20V, and welding speed 0.6m/min.
  • the amount of spatter generation was compared by imaging 5 times every 5 seconds immediately after the start of welding, and the welding pore rate was measured by measuring the distribution rate (%) of pore defects on the weld line after radioactive non-destructive testing of the welded zone.
  • the weight% content of Mg from the surface of the plated layer to the 2/3t position in the thickness direction satisfied ⁇ 0.5wt% based on an average weight% content of Mg in the plated layer, corrosion resistance was superior to that of embodiments 1 to 6.
  • comparative examples 2 and 4 satisfied the Mg content of the plated layer and ensured corrosion resistance, but did not satisfy relational expressions 1 and 2, such that the Al content was excessive on the surface of the plated layer, and phosphatability and weldability were extremely poor.

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EP22876842.0A 2021-09-30 2022-09-28 Tôle d'acier plaquée présentant d'excellentes propriétés de résistance à la corrosion et de soudabilité, et son procédé de fabrication Pending EP4411016A1 (fr)

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PCT/KR2022/014553 WO2023055070A1 (fr) 2021-09-30 2022-09-28 Tôle d'acier plaquée présentant d'excellentes propriétés de résistance à la corrosion et de soudabilité, et son procédé de fabrication

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