SG194952A1 - Molten zn-al-based alloy-plated steel sheet having excellent corrosion resistance and workability, and method for producing same - Google Patents
Molten zn-al-based alloy-plated steel sheet having excellent corrosion resistance and workability, and method for producing same Download PDFInfo
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- SG194952A1 SG194952A1 SG2013084314A SG2013084314A SG194952A1 SG 194952 A1 SG194952 A1 SG 194952A1 SG 2013084314 A SG2013084314 A SG 2013084314A SG 2013084314 A SG2013084314 A SG 2013084314A SG 194952 A1 SG194952 A1 SG 194952A1
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 96
- 239000010959 steel Substances 0.000 title claims abstract description 96
- 230000007797 corrosion Effects 0.000 title claims abstract description 38
- 238000005260 corrosion Methods 0.000 title claims abstract description 38
- 238000004519 manufacturing process Methods 0.000 title claims description 8
- 239000011248 coating agent Substances 0.000 claims abstract description 88
- 238000000576 coating method Methods 0.000 claims abstract description 88
- 239000011247 coating layer Substances 0.000 claims abstract description 84
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 55
- 239000000956 alloy Substances 0.000 claims abstract description 55
- 229910007570 Zn-Al Inorganic materials 0.000 claims abstract description 53
- 239000010410 layer Substances 0.000 claims abstract description 21
- 238000000034 method Methods 0.000 claims abstract description 14
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 10
- 239000000758 substrate Substances 0.000 claims description 21
- 239000000203 mixture Substances 0.000 claims description 16
- 239000012535 impurity Substances 0.000 claims description 9
- 238000001816 cooling Methods 0.000 claims description 4
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 35
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 26
- 230000000052 comparative effect Effects 0.000 description 12
- 238000012360 testing method Methods 0.000 description 9
- 230000000694 effects Effects 0.000 description 7
- 229910018134 Al-Mg Inorganic materials 0.000 description 4
- 229910018467 Al—Mg Inorganic materials 0.000 description 4
- 229910001335 Galvanized steel Inorganic materials 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 239000008397 galvanized steel Substances 0.000 description 4
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 4
- 229910000838 Al alloy Inorganic materials 0.000 description 3
- 238000005452 bending Methods 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 239000007921 spray Substances 0.000 description 3
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 229910000905 alloy phase Inorganic materials 0.000 description 2
- 238000005275 alloying Methods 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 239000004566 building material Substances 0.000 description 2
- 230000015556 catabolic process Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000010960 cold rolled steel Substances 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 238000006731 degradation reaction Methods 0.000 description 2
- 230000005496 eutectics Effects 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 238000005246 galvanizing Methods 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 239000002932 luster Substances 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- 241001163841 Albugo ipomoeae-panduratae Species 0.000 description 1
- 229910000611 Zinc aluminium Inorganic materials 0.000 description 1
- HXFVOUUOTHJFPX-UHFFFAOYSA-N alumane;zinc Chemical compound [AlH3].[Zn] HXFVOUUOTHJFPX-UHFFFAOYSA-N 0.000 description 1
- 239000008199 coating composition Substances 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 238000012790 confirmation Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
Classifications
-
- 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
- C23C2/34—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
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Coating With Molten Metal (AREA)
Abstract
A steel sheet is Immersed into a hot-dip Zn-Al alloy coating bath containing Al: 3 to 6%, Mg: 0.2 to 1.0%, Ni: 0.01 to 0.10%, and 0.10% or less of Fe in terms of percent by mass, withdrawn therefrom, and cooled to form a hot-dip Zn-Al alloy coating layer on surfaces of the steel sheet. During this process, the bath temperature of the coating bath is adjusted to be within a range of 420°C to 520°C and the sheet temperature of the steel sheet upon immersing into the coating bath is adjusted to be within a range of 420°C to 600°C but not less than the bath temperature of the coating bath. As a result, a hot-dip Zn-Al alloy coated steel sheet having high formability and high corrosion resistance and including a coating layer having an Fe content of 2.0 g/m2 or less and a Ni-rich layer having a thickness of 0.05 to 1.0 gm at the Interface between the coating layer and the steel sheet is obtained.
Description
- 1 =
HOT-DIP ZINC-ALUMINUM ALLOY COATED STEEL SHEET HAVING HIGH
CORROSION RESISTANCE AND FORMABILITY AND METHOD FOR
PRODUCING THE SAME
The present invention relates to a hot-dip Zn-Al alloy coated steel sheet suitable for use in construction, civil engineering, household electric appliances, etc., and a method for producing the sheet. In particular, it relates to improvements in formability and corrosion resistance of formed portions.
In the fields of building materials, household electric appliances, automobiles, etc., hot-dip galvanized steel sheets have been widely used. Hot-dip Zn coated steel sheets applied to such usages are mainly required to exhibit high corrosion resistance. However, for example, in the field of construction, hot-dip galvanized steel sheets are formed into particular shapes and used as parts of roofs, walls, structures, etc., and thus hot-dip galvanized steel sheets for such usages are required to exhibit not only high corrosion resistance but also high formability and,
furthermore, high corrosion resistance in formed portions.
In the fields of building materials and household electric appliances, for example, the sheets are frequently used unpainted and are thus required to excel also in uniformity of appearance and blackening resistance.
To meet such requirements, for example, Patent
Literature 1 proposes a hot-dip Zn-Al alloy coated steel sheet that has good coating appearance with metallic luster and high blackening resistance. In the technique described in Patent Literature 1, a steel sheet is immersed into a hot-dip Zn-Al alloy coating bath, withdrawn from the coating bath, and cooled at a cooling rate of 1 to 15°C/s to 250°C so as to form a hot-dip Zn-Al alloy coating layer composed of Al: 1.0 to 10%, Mg: 0.2 to 1.0%, Ni: 0.005 to 0.1%, and the balance being Zn and unavoidable impurities on surfaces of the steel sheet, thereby producing a hot-dip Zn-Al alloy coated steel sheet having good coating appearance with metallic luster and high blackening resistance. In the technique described in Patent Literature 1, the cooling rate after coating is controlled to be within the aforementioned particular range to accelerate condensation of Ni in the outermost surface portion of the coating due to a synergetic effect of Mg and Ni.
Patent Literature 2 describes a technique related to a hot-dip galvanized steel sheet having high corrosion resistance. A coated steel sheet described in Patent
Literature 2 has, on surfaces of a steel sheet, a hot-dip
Zn-Al alloy coating layer composed of, in terms of mass$,
Al: 1.0 to 10%, Mg: 0.2 to 1.0%, Ni: 0.005 to 0.2%, and the balance being Zn and unavoidable impurities, and a Ni-rich layer at the interface between the coating layer and the base steel sheet. According to this technique, the coating layer exhibits high formability, cracking in formed portions is suppressed, and thus corrosion of the base steel sheet is suppressed, thereby producing a coated steel sheet having high corrosion resistance in formed portions.
Patent Literature
PTL 1: Japanese Unexamined Patent Application
Publication No. 2008-138285
PTL 2: Japanese Unexamined Patent Application
Publication No. 2010-255084
In the technique described in Patent Literature 1, a
Zn-Al-Mg coating layer containing Ni is used to mainly improve the blackening resistance. However, Patent
Literature 1 makes no mention as to the amount of Fe in the coating layer. For example, when Fe contained in the coating bath is excessively incorporated into the coating layer and a thick alloy phase is formed between the coating layer and the substrate, the coating layer becomes susceptible to cracks on forming such as bending. The coating layer becomes thin in cracked portions and exposure of the base steel sheet may sometimes result. Accordingly, a coated steel sheet produced by the technique described in
Patent Literature 1 has suffered from low formability and low corrosion resistance in formed portions as a natural consequence.
In the technique described in Patent Literature 2, a coated steel sheet having high formability and high corrosion resistance in formed portions is obtained.
However, Patent Literature 2 makes no mention as to the amount of Fe in the coating layer. Accordingly, as with the coated steel sheet produced by the technique described in
Patent Literature 1, there has been a problem in that when
Fe in the coating bath is excessively incorporated into the coating layer and the steel sheet is subjected to forming such as bending, cracks readily occur in the coating layer, resulting in low formability and low corrosion resistance in formed portions.
Patent Literature 2 merely describes that the sheet immersing temperature of the steel sheet upon immersing into the coating bath is appropriately controlled to be within the range of 450°C to 600°C and the coating bath temperature is appropriately controlled to be within the range of 400°C to 550°C both on the basis of the sheet thickness and the line speed, and makes no mention of a clear and specific production process. Moreover, in Patent Literature 2, no confirmation is made on effects achieved by the production method.
An object of the present invention is to provide a hot- dip Zn-Al alloy coated steel sheet having both high corrosion resistance and high formability and a method for producing the sheet.
The inventors of the invention of the subject application have carried out extensive studies on various factors that affect the corrosion resistance and formability of a hot-dip Zn-Al alloy coated steel sheet to achieve the object described above. As a result, the inventors have found that in order to improve coating adherence, corrosion resistance, and corrosion resistance after forming, it is preferable to use a coating bath having a Zn-Al-Mg alloy coating composition containing an adequate amount of Ni, adjust the bath temperature of the coating bath to a temperature within an adequate range, and adjust the temperature of a steel sheet (sheet temperature), which serves as a substrate, upon immersing into the coating bath to be within an adequate range but not less than the bath a _ temperature of the coating bath. The inventors have found that, in this manner, a Ni-rich layer having an adequate thickness can be formed at the interface between the coating layer and the substrate, i.e., the steel sheet (base steel sheet) .
The inventors have also found that in order to stably improve the formability of the coating layer, the Fe content in the coating layer must be adjusted to 2.0 g/m” or less per unit area of the coating layer. The inventors have found that Fe contained in the coating layer is incorporated therein by solidification of Fe in the coating bath and that in order to adjust the Fe content in the coating layer to a desired value or less, the Fe concentration in the coating bath may be adjusted to an adequate level, in particular, 0.05% or less in terms of mass%.
The present invention has been made based on these findings and further studies. The present invention is summarized as follows. (1) A method for producing a hot-dip Zn-Al alloy coated steel sheet having high corrosion resistance and high formability, the method including introducing a steel sheet serving as a substrate into a hot-dip Zn-Al alloy coating bath having a composition of Al: 3 to 6%, Mg: 0.2 to 1.0%,
Ni: 0.01 to 0.10%, and the balance being Zn and unavoidable impurities in terms of percent by mass, withdrawing the steel sheet therefrom, and cooling the steel sheet to form a hot-dip Zn-Al alloy coating layer on a surface of the steel sheet. The hot-dip Zn-Al alloy coating bath has an Fe content adjusted to 0.10% or less, a temperature of the hot- dip Zn-Al alloy coating bath is adjusted to be within a range of 420°C to 520°C, and a temperature of the steel sheet upon immersing into the hot-dip Zn-Al alloy coating bath is adjusted to be within a range of 420°C to 600°C but not less than the temperature of the hot-dip Zn-Al alloy coating bath. (2) A hot-dip Zn-Al alloy coated steel sheet having high corrosion resistance and high formability, including a steel sheet serving as a substrate and a hot-dip Zn-Al alloy coating layer having a composition of Al: 3 to 6%, Mg: 0.2 to 1.0%, Ni: 0.01 to 0.10%, and the balance being Zn and unavoidable impurities in terms of percent by mass, the hot- dip Zn-Al alloy coating layer being formed on at least one surface of the steel sheet. The hot-dip Zn-Al alloy coating layer has an Fe content adjusted to 2.0 g/m? or less and a
Ni-rich layer having a thickness of 0.05 to 1.0 pm lies at the interface between the hot-dip Zn-Al alloy coating layer and the steel sheet.
According to the present invention, formability as well as corrosion resistance is improved and thus the present invention has an advantageous effect that a hot-dip Zn-Al alloy coated steel sheet having both high corrosion resistance and high formability can be easily produced at low cost. Another advantageous effect of the present invention is that the adherence of the coating layer is improved.
First, a method for producing a hot-dip Zn-Al alloy coated steel sheet of the present invention (hereinafter may be referred to as "coated steel sheet of the invention") is described.
A steel sheet used as a substrate is, for example, immersed into a hot-dip Zn-Al alloy coating bath by using a continuous galvanizing line, withdrawn therefrom, and cooled to form a hot-dip Zn-Al alloy coating layer on surfaces of the steel sheet.
The type and composition of the steel sheet used as the substrate need not be limited and may be appropriately selected from known hot-rolled steel sheets and cold-rolled steel sheets according to the intended use.
The steel sheet serving as the substrate is, for example, first heated to a desired heating temperature by using a continuous galvanizing line. The heating temperature may be appropriately determined according to the steel sheet used and is not particularly limited. However,
in the present invention, at the time the steel sheet is immersed into the coating bath, the steel sheet temperature (sheet temperature) must be adjusted to a particular desired temperature. In this regard, the heating temperature must at least be a temperature with which a desired steel sheet temperature (sheet temperature) can be achieved upon immersing of the steel sheet into the coating bath.
The steel sheet heated to a particular temperature is immersed into a hot-dip Zn-Al alloy coating bath having a particular composition maintained at a particular bath temperature to form a hot-dip Zn-Al alloy coating layer on surfaces of the steel sheet.
The composition of the hot-dip Zn-Al alloy coating bath into which the steel sheet is immersed contains, in terms of mass%, Al: 3 to 6%, Mg: 0.2 to 1.0%, Ni: 0.01 to 0.10%, and the balance being Zn and unavoidable impurities. In the present invention, the coating bath has an Fe content adjusted to 0.10% or less.
The reasons for the limitations on the composition of the coating bath are as follows. Note that % used in describing the composition denotes mass%.
Al: 3 to 6%
When the Al content in the coating bath is less than 3%, a thick Fe-Al alloy layer is likely to be formed at the interface between the coating layer to be formed and the base steel sheet (substrate), resulting in degradation of formability of the coating layer. At an Al content exceeding 6%, the sacrificial protection effect of Zn on the coating layer is reduced and the corrosion resistance of the coated steel sheet end surface portions and the like is degraded. When the Al content in the coating bath exceeds 6%, top dross mainly composed of Al tends to occur and the appearance of the resulting coating layer is degraded.
Furthermore, the blackening resistance of the resulting coating layer is degraded, formation of the Zn-Al-Mg ternary eutectic is enhanced, and the formability of the coating layer is degraded. Thus, the Al content in the coating bath is limited to a range of 3 to 6%.
Mg: 0.2 to 1.0%
In order to improve the corrosion resistance, in particular, the blackening resistance, of the coating layer to be formed, Mg is added to the coating bath. When the Mg content in the coating bath is less than 0.2%, the effect of improving the corrosion resistance of the coating layer to be formed is small. In contrast, at an Mg content exceeding 1.0%, an excessively large amount of Zn-Al-Mg ternary eutectic is formed in the resulting coating layer and the formability of the coating layer is degraded. Thus, the Mg content in the coating bath is limited to a range of 0.2 to 1.0%.
Ni: 0.01 to 0.10%
Nickel is added to the coating bath in order to improve the corrosion resistance of the coating layer to be formed.
At a Ni content less than 0.01%, the effect of improving the corrosion resistance is small. In contrast, at a Ni content exceeding 0.10%, the surface of the coating layer to be obtained will be excessively activated and become susceptible to corrosion, leading to formation of white rust at an early stage. Thus, the Ni content in the coating bath is limited to a range of 0.01 to 0.10%.
The balance is composed of Zn and unavoidable impurities.
The coating bath used in the present invention has an
Fe content adjusted to 0.10% or less in terms of mass$%.
Iron is not intentionally added to the coating bath.
However, during the coating treatment, Fe is dissolved from the steel sheet immersed into the coating bath and stays in the coating bath. Iron in the coating bath becomes incorporated into the coating layer as the coating solution adhering to the surfaces of the steel sheet solidifies and forms a coating layer. When a large amount of Fe is incorporated into the coating layer, a thick alloy phase is formed and thus the formability of the coating layer is degraded. According to studies carried out by the inventors, the Fe content in the coating layer needs to be adjusted to a particular value (2.0 g/m?) or less in order to suppress degradation of the formability of the coating layer. In order to control the Fe content in the coating layer to a particular value or less, it is important that the Fe concentration in the coating bath be appropriately controlled to 0.10% or less. Note that since the Fe content in the coating layer is dependent on the coating layer thickness, the Fe content herein is expressed as content per unit area (g/m?) .
In the present invention, the temperature of the coating bath adjusted to produce the above-described composition is adjusted to be within a range of 420°C to 520°C. If the temperature of the coating bath is less than 420°C, the viscosity of the coating bath increases due to the excessively low bath temperature and the desired coating treatment cannot be carried out. In contrast, when the temperature exceeds 520°C, the coating bath is excessively oxidized and extensive dross formation occurs. Thus, the temperature of the coating bath is limited to a range of 420°C to 520°C.
A steel sheet serving as a substrate is immersed into a coating bath adjusted to have such a composition and a bath temperature.
In the present invention, the temperature of the steel sheet (sheet temperature) upon immersing into the coating bath is adjusted to be within a range of 420°C to 600°C but not lower than the bath temperature of the coating bath. If the sheet temperature of the steel sheet upon immersing is lower than the temperature of the coating bath, the temperature of the coating bath will decrease gradually, thereby causing the viscosity of the coating bath to increase and obstructing the operation. In contrast, at a temperature exceeding 600°C, the temperature of the coating bath will gradually increase. Thus the temperature of the steel sheet (sheet temperature) upon immersing into the coating bath is limited to a range of 420°C to 600°C but not lower than the temperature of the coating bath.
In the present invention, the coating bath having the aforementioned composition is adjusted to a temperature within the range described above and the temperature of the steel sheet (sheet temperature) upon immersing into the coating bath is adjusted to be within a range of 420°C to 600°C but not lower than the temperature of the coating bath.
As a result, alloying elements diffuse at the interface between the coating bath and the steel sheet surface and formation of an adequate Ni-rich layer is accelerated at the interface between the coating layer and the steel sheet (substrate). Since the Ni-rich layer is formed, the corrosion resistance can be improved even when damage reaching the substrate occurs in the coating layer or cracks occur in the coating layer due to forming. The thickness of the Ni-rich layer can be controlled to be within an adequate range of 0.05 to 1 um by adjusting the coating bath composition, the bath temperature, and the sheet temperature of the steel sheet upon immersing to be within the aforementioned ranges.
The steel sheet having been immersed into the coating bath is then withdrawn from the coating bath and cooled.
A coated steel sheet of the invention produced by the process described above is a hot-dip Zn-Al alloy coated steel sheet having a hot-dip Zn-Al alloy coating layer constituting at least one surface thereof, the layer containing, in terms of mass%, Al: 3.0 to 6.0%, Mg: 0.2 to 1.0%, Ni: 0.01 to 0.10%, 2.0 g/m? or less of Fe, and the balance being Zn and unavoidable impurities; and a Ni-rich layer having a thickness of 0.05 to 1 um at the interface between the coating layer and a steel sheet.
The reasons for the limitations on the composition of the hot-dip Zn-Al alloy coating layer are the same as the reasons for the limitations on the coating bath described above and description thereof is omitted. The coating weight of the hot-dip Zn-Al alloy coating layer may be set according to the intended use as usual and no limitation is imposed thereon. However, the coating weight of the hot-dip zn-Al alloy coating layer is preferably about 30 to 300 g/m’
per side. When the coating weight is less than 30 g/m?, the thickness of the coating layer is insufficient and the desired corrosion resistance cannot be maintained. When the coating weight exceeds 300 g/m”, the thickness of the coating layer increases excessively and peeling off of the coating layer easily occurs.
The coated steel sheet of the invention includes a Ni- rich layer at the interface between the coating layer and the base steel sheet (substrate). As a result, the corrosion resistance of the coating layer can be maintained even when damage reaching the base steel sheet (substrate) occurs in the coating layer or cracks occur in the coating layer due to forming. The thickness of the Ni-rich layer is to be within a range of 0.05 to 1.0 um. When the thickness of the Ni-rich layer is less than 0.05 um, the reaction between the coating layer and the base steel sheet (substrate) is insufficient and thus the coating adherence is insufficient. In contrast, when the thickness exceeds 1.0 pm, the formability of the coating layer is degraded.
Accordingly, the thickness of the Ni-rich layer formed at the interface between the coating layer and the base steel sheet (substrate) is limited to be within a range of 0.05 to 1.0 Mm.
The Ni-rich layer is formed by an alloying reaction between Ni in the coating bath and Fe on a steel sheet surface. The thickness of the Ni-rich layer can be adjusted to be within a particular range by appropriately controlling the coating bath temperature, the steel sheet, and the sheet immersing temperature as described above. [EXAMPLES]
A cold-rolled steel sheet (sheet thickness: 0.5 mm, unannealed) was used as the substrate. The substrate was heated so that the substrate would have a sheet immersing temperature (sheet temperature) shown in Table 1 upon immersing into the coating bath, immersed into a hot-dip Zn-
Al alloy coating bath having various compositions and bath temperatures shown in Table 1, withdrawn therefrom, and cooled to form a hot-dip Zn-Al alloy coating layer having a coating weight shown in Table 2.
The coating layer of the resulting hot-dip Zn-Al alloy coated steel sheet was melted and the composition of the coating layer was analyzed by a common method. Using the resulting hot-dip Zn-Al alloy coated steel sheet, observation of the microstructure in a cross-section of the coating layer, a formability test, and a corrosion test of bended portions were conducted. The test methods were as follows. (1) Observation of microstructure in cross-section of coating layer
A test specimen for microstructural observation was
- 17 = taken from the resulting hot-dip Zn-Al alloy coated steel sheet. A section taken in the sheet thickness direction was polished and the microstructure of the section of the coating layer was observed in 10 or more observation areas using a scanning electron microscope (2000x magnification) to analyze Ni. Whether the Ni-rich layer was present and the thicknesses of the Ni-rich layer were determined and the average thicknesses were calculated. Note that the term "Ni-rich layer" refers to a region where a peak attributable to Ni is detected with an energy-dispersive X-ray spectrometer of a scanning electron microscope. (2) Formability test
A JIS No. 5 tensile test specimen was taken from the resulting hot-dip Zn-Al alloy coated steel sheet and subjected to a tensile test. During the test, the surface of the coating layer was observed with the naked eye, the amount of strain at which cracks are identifiable in the coating layer surface (crack-generating strain amount) was determined, and the formability of the coated steel sheet was evaluated. The evaluation standard was as follows.
Rating AA: The crack-generating strain amount was 20% or more.
Rating A: The crack-generating strain amount was 10% or more and less than 20%.
Rating B: The crack-generating strain amount was 5% or more and less than 10%.
Rating C: The crack-generating strain amount was less than 5%. (3) Corrosion resistance test on bended portions
The resulting hot-dip Zn-Al alloy coated steel sheet was subjected to 1R-180° bending and a salt spray test was carried out in accordance with JIS Z 2371. Salt spray conditions were as follows: spray solution: 5% NaCl solution, temperature: 35°C, testing hours: 1000 h. After the test, the surface of the specimen was observed with the naked eye and the red rust generation ratio (area fraction) was determined to evaluate the corrosion resistance of the bended portions. The standard of the evaluation was as follows.
Rating A: No red rust
Rating B: Red rust generation ratio of 1 to 50%
Rating C: Red rust generation ratio of 51% or more
The results are shown in Table 2.
[Table 1]
Sheet
Steel rare Bath (Sheet temperature) sheet | - (bath temperature) Remarks immersin temperature . ° bath) (°C 6 | 530 | 500 | 45 | 05 | 005] 002 | Balance | ~~ 30 | Invention Example 8 | 570 | 510 | 45] 05 [005] 002 | Balance | ~~ 60 | InventionExample 9 | 50 | 530 | 45 | 05 | 005] 0.02 | Balance | ~~ 30 | Comparative Example | 480 | 460 | 45 | 05 | - | 0.02 | Balance | ~~ 20 | Comparative Example
[Table 2]
Corrosion
Microstructure in cross- i.
Steel Coating layer section of coating layer Formability b resistance of s sheet Coating [qr — Remarks
No. weiaht Thickness of Ni-rich layer Ratin Ratin
Gin (um) ; ; 1 [45] 05 ]005/Balance| 005 | 90 [ ~~ 003 ~~ | B | A | Comparative Example 2 [45] 05 [005/Balance| 015 | 90 | ~~ 010 | AA | A | Invention Example 3 [45] 05 ]005/Balance| O27 | 90 [| ~~ 015 ~~ | AA | A | Invention Example 4 [45] 05 ]005/Balance| 032 | 90 [| ~~ 020 | AA | A | Invention Example
[45] 05 [005/Balance| 061 | 90 | ~~ 030 | AA | A | Invention Example 6 [45] 05 ]005/Balance| 0.78 | 90 [| ~~ 040 | AA | A | Invention Example 7 [45] 05 ]005/Balance| 089 | 9 [| ~~ 060 | A | A | Invention Example 8 [45] 05 [005/Balance| 143 | 9 | ~~ 070 | A | A | Invention Example 9 |45[05 [005/Balance| 212 | 90 | ~~ 110 ~~ | C€ | ~~ B | Comparative Example
[45] 05 |0.05|Balance| 225 | 90 [| ~~ 045 ~~ [| CC | ~~ C | Comparative Example 11 [29] 05 J005|Balance| 245 | 90 [| ~~ 125 ~~ | C | ~~ C | Comparative Example 12 [65] 05 [0.05/Balance| 055 | 90 [| ~~ 035 ~~ | B | ~~ B | Comparative Example 13 [45] 01 ]005|Balance| 043 | 90 [ 025 ~~ | A | ~~ B | Comparative Example 14 [45] 12 |005/Balance| 039 | 90 [ ~~ 025 ~~ | C | A | Comparative Example 1514505 | - [Balance 034 | 9% | ~~ - ~~ | A | ~~ B | Comparative Example 16 [45] 05 [012[Balance| 029 | 90 [ ~~ 03 | A | CC | Comparative Example
In all of the invention examples, hot-dip Zn-Al alloy coated steel sheets having high formability and corrosion resistance at formed portions were obtained. In contrast,
Comparative Examples outside the range of the present invention exhibited low formability or low corrosion resistance in formed portions or both.
Claims (2)
- [Claim 1] A method for producing a hot-dip Zn-Al alloy coated steel sheet having high corrosion resistance and high formability, the method comprising introducing a steel sheet serving as a substrate into a hot-dip Zn-Al alloy coating bath having a composition of Al: 3 to 6%, Mg: 0.2 to 1.0%, Ni: 0.01 to 0.10%, and the balance being Zn and unavoidable impurities in terms of percent by mass, withdrawing the steel sheet therefrom, and cooling the steel sheet to form a hot-dip Zn-Al alloy coating layer on a surface of the steel sheet, wherein the hot-dip Zn-Al alloy coating bath has an Fe content adjusted to 0.1% or less, a temperature of the hot- dip Zn-Al alloy coating bath is adjusted to be within a range of 420°C to 520°C, and a temperature of the steel sheet upon immersing into the hot-dip Zn-Al alloy coating bath is adjusted to be within a range of 420°C to 600°C but not less than the temperature of the hot-dip Zn-Al alloy coating bath.
- [Claim 2] A hot-dip Zn-Al alloy coated steel sheet having high corrosion resistance and high formability, comprising a steel sheet serving as a substrate and a hot-dip Zn-Al alloy coating layer having a composition of Al: 3 to 6%, Mg: 0.2 to 1.0%, Ni: 0.01 to 0.10%, and the balance being Zn and unavoidable impurities in terms of percent by mass, the hot- dip Zn-Al alloy coating layer being formed on at least one surface of the steel sheet,wherein the hot-dip Zn-Al alloy coating layer has an Fe content adjusted to 2.0 g/m’ or less and a Ni-rich layer having a thickness of 0.05 to 1.0 mm lies at the interface between the hot-dip Zn-Al alloy coating layer and the steel sheet.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2011120550A JP5649179B2 (en) | 2011-05-30 | 2011-05-30 | Hot-dip Zn-Al alloy-plated steel sheet with excellent corrosion resistance and workability and method for producing the same |
| PCT/JP2012/064344 WO2012165644A1 (en) | 2011-05-30 | 2012-05-29 | Molten zn-al-based alloy-plated steel sheet having excellent corrosion resistance and workability, and method for producing same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| SG194952A1 true SG194952A1 (en) | 2013-12-30 |
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| Application Number | Title | Priority Date | Filing Date |
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| SG2013084314A SG194952A1 (en) | 2011-05-30 | 2012-05-29 | Molten zn-al-based alloy-plated steel sheet having excellent corrosion resistance and workability, and method for producing same |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JP5649179B2 (en) |
| KR (1) | KR101598677B1 (en) |
| CN (1) | CN103562430B (en) |
| AU (1) | AU2012263323B2 (en) |
| MY (1) | MY161932A (en) |
| SA (1) | SA112330553B1 (en) |
| SG (1) | SG194952A1 (en) |
| TW (1) | TWI484068B (en) |
| WO (1) | WO2012165644A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2015052546A1 (en) * | 2013-10-09 | 2015-04-16 | ArcelorMittal Investigación y Desarrollo, S.L. | Sheet metal having a znaimg coating and improved flexibility and corresponding production method |
| MY165610A (en) * | 2015-04-08 | 2018-04-16 | Nippon Steel & Sumitomo Metal Corp | Zn-Al-Mg COATED STEEL SHEET, AND METHOD OF PRODUCING Zn-Al-Mg COATED STEEL SHEET |
| KR102059048B1 (en) * | 2015-09-29 | 2019-12-24 | 닛폰세이테츠 가부시키가이샤 | Zn alloy clad steel containing Mg |
| AU2018234211B2 (en) * | 2017-03-17 | 2020-07-23 | Nippon Steel Corporation | Coated Steel Sheet |
| KR102297298B1 (en) * | 2019-12-06 | 2021-09-03 | 주식회사 포스코 | Galvanizing steel sheet having excelent bendability and corrosion resistance, and manufacturing method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPH0688178A (en) * | 1992-09-04 | 1994-03-29 | Sumitomo Metal Ind Ltd | Method for removing dross |
| JP2001262303A (en) * | 2000-03-21 | 2001-09-26 | Kawasaki Steel Corp | Method for producing alloyed galvanized steel sheet and galvannealed steel sheet excellent in hot dip metal coated property |
| JP2005146339A (en) * | 2003-11-14 | 2005-06-09 | Nisshin Steel Co Ltd | HOT DIP Al-CONTAINING GALVANNEALED STEEL SHEET HAVING EXCELLENT BLACKENING RESISTANCE |
| JP5101249B2 (en) * | 2006-11-10 | 2012-12-19 | Ｊｆｅ鋼板株式会社 | Hot-dip Zn-Al alloy-plated steel sheet and method for producing the same |
| JP5600398B2 (en) * | 2009-04-28 | 2014-10-01 | Ｊｆｅ鋼板株式会社 | Hot-dip galvanized steel sheet |
-
2011
- 2011-05-30 JP JP2011120550A patent/JP5649179B2/en active Active
-
2012
- 2012-05-28 SA SA112330553A patent/SA112330553B1/en unknown
- 2012-05-29 SG SG2013084314A patent/SG194952A1/en unknown
- 2012-05-29 KR KR1020137029051A patent/KR101598677B1/en active IP Right Grant
- 2012-05-29 WO PCT/JP2012/064344 patent/WO2012165644A1/en active Application Filing
- 2012-05-29 MY MYPI2013702124A patent/MY161932A/en unknown
- 2012-05-29 AU AU2012263323A patent/AU2012263323B2/en active Active
- 2012-05-29 CN CN201280026450.7A patent/CN103562430B/en active Active
- 2012-05-30 TW TW101119272A patent/TWI484068B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| TW201303077A (en) | 2013-01-16 |
| AU2012263323A1 (en) | 2013-11-21 |
| CN103562430B (en) | 2015-11-25 |
| CN103562430A (en) | 2014-02-05 |
| TWI484068B (en) | 2015-05-11 |
| SA112330553B1 (en) | 2015-07-09 |
| MY161932A (en) | 2017-05-15 |
| KR20140043337A (en) | 2014-04-09 |
| JP2012246547A (en) | 2012-12-13 |
| KR101598677B1 (en) | 2016-02-29 |
| WO2012165644A1 (en) | 2012-12-06 |
| JP5649179B2 (en) | 2015-01-07 |
| AU2012263323B2 (en) | 2015-07-02 |
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