KR19990011059A - A method of manufacturing a hot-dip galvanized steel sheet excellent in surface shape and corrosion resistance - Google Patents
A method of manufacturing a hot-dip galvanized steel sheet excellent in surface shape and corrosion resistance Download PDFInfo
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- KR19990011059A KR19990011059A KR1019970034000A KR19970034000A KR19990011059A KR 19990011059 A KR19990011059 A KR 19990011059A KR 1019970034000 A KR1019970034000 A KR 1019970034000A KR 19970034000 A KR19970034000 A KR 19970034000A KR 19990011059 A KR19990011059 A KR 19990011059A
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- corrosion resistance
- steel sheet
- plating
- hot
- dip galvanized
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- 238000005260 corrosion Methods 0.000 title claims abstract description 53
- 230000007797 corrosion Effects 0.000 title claims abstract description 53
- 229910001335 Galvanized steel Inorganic materials 0.000 title abstract description 20
- 239000008397 galvanized steel Substances 0.000 title abstract description 20
- 238000004519 manufacturing process Methods 0.000 title description 6
- 238000007747 plating Methods 0.000 claims abstract description 65
- AMWRITDGCCNYAT-UHFFFAOYSA-L hydroxy(oxo)manganese;manganese Chemical compound [Mn].O[Mn]=O.O[Mn]=O AMWRITDGCCNYAT-UHFFFAOYSA-L 0.000 claims abstract description 20
- 239000011248 coating agent Substances 0.000 claims description 7
- 238000000576 coating method Methods 0.000 claims description 7
- 229910000831 Steel Inorganic materials 0.000 claims description 4
- 238000001816 cooling Methods 0.000 claims description 4
- 239000010959 steel Substances 0.000 claims description 4
- 239000010960 cold rolled steel Substances 0.000 claims description 2
- 238000000034 method Methods 0.000 abstract description 12
- ZCDOYSPFYFSLEW-UHFFFAOYSA-N chromate(2-) Chemical compound [O-][Cr]([O-])(=O)=O ZCDOYSPFYFSLEW-UHFFFAOYSA-N 0.000 abstract description 5
- 230000000694 effects Effects 0.000 abstract description 4
- 239000011701 zinc Substances 0.000 description 21
- 239000011572 manganese Substances 0.000 description 15
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 13
- 229910052725 zinc Inorganic materials 0.000 description 13
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 5
- 239000000243 solution Substances 0.000 description 5
- 230000010287 polarization Effects 0.000 description 4
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 238000005275 alloying Methods 0.000 description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 230000006866 deterioration Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 150000003839 salts Chemical class 0.000 description 3
- 239000007921 spray Substances 0.000 description 3
- 241001163841 Albugo ipomoeae-panduratae Species 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 239000000654 additive Substances 0.000 description 2
- 230000000996 additive effect Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 2
- 229910052748 manganese Inorganic materials 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 1
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- 229910000914 Mn alloy Inorganic materials 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- KRVSOGSZCMJSLX-UHFFFAOYSA-L chromic acid Substances O[Cr](O)(=O)=O KRVSOGSZCMJSLX-UHFFFAOYSA-L 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 239000011651 chromium Substances 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 238000003411 electrode reaction Methods 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- AWJWCTOOIBYHON-UHFFFAOYSA-N furo[3,4-b]pyrazine-5,7-dione Chemical compound C1=CN=C2C(=O)OC(=O)C2=N1 AWJWCTOOIBYHON-UHFFFAOYSA-N 0.000 description 1
- 238000005246 galvanizing Methods 0.000 description 1
- 229910001385 heavy metal Inorganic materials 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- WJZHMLNIAZSFDO-UHFFFAOYSA-N manganese zinc Chemical compound [Mn].[Zn] WJZHMLNIAZSFDO-UHFFFAOYSA-N 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 239000000741 silica gel Substances 0.000 description 1
- 229910002027 silica gel Inorganic materials 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 239000004575 stone Substances 0.000 description 1
- 230000037303 wrinkles Effects 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
- C23C2/26—After-treatment
- C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
- C23C2/29—Cooling or quenching
-
- 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)
- Physics & Mathematics (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Thermal Sciences (AREA)
- Coating With Molten Metal (AREA)
Abstract
본 발명은 용융아연 도금강판의 나내식성을 향상시키는 방법에 관한 것으로 특히 0.3∼0.5wt.% Mn-Zn계 도금욕에서 475∼600℃의 도금욕 온도로 도금하는 단계와, 공기중에서 자연냉각하여 산화망간피막을 형성하는 단계로 이루어진 표면형상 및 내식성이 우수한 용융아연 도금강판 제조방법에 관한 것이다.The present invention relates to a method of improving the corrosion resistance of a hot-dip galvanized steel sheet, particularly a step of plating at a plating bath temperature of 475 to 600 ° C in a 0.3 to 0.5 wt.% Mn-Zn based plating bath, And a step of forming a manganese oxide film on the surface of the hot dip galvanized steel sheet.
상기와 같은 구성의 본 발명에 의하여 도금 부착량의 증대 및 추가의 크로메이트 처리가 필요 없어 경제적이며, 불필요한 공정의 제거로 생산성을 향상시키는 효과를 제공한다.According to the present invention having the above-described structure, it is not necessary to increase the plating amount and further chromate treatment, and it is economical and provides an effect of improving the productivity by eliminating unnecessary processes.
Description
본 발명은 용융아연 도금강판의 나내식성을 향상시키는 방법에 관한 것으로 특히 아연도금욕에 합금원소의 첨가와 산화피막의 형성으로 용융아연 도금강판의 나내식성을 향상시키는 것을 특징으로 하는 표면형상 및 내식성이 우수한 용융아연 도금강판 제조방법에 관한 것이다.The present invention relates to a method for improving the corrosion resistance of a hot-dip galvanized steel sheet, and more particularly, to a method for improving the corrosion resistance of a hot-dip galvanized steel sheet by adding an alloy element to a zinc plating bath and forming an oxide film, And a method of manufacturing the hot-dip galvanized steel sheet.
일반적으로 용융아연도금은 저렴하면서 뛰어난 희생방식 작용으로 오랜 전부터 효과적인 방청처리 방법으로 널리 사용되고 있다.Generally, hot-dip galvanizing is widely used as an effective anti-rust treatment method for a long time with an inexpensive and excellent sacrificial action.
이것은 아연의 수소 과전압이 크고 수소발생에 대한 교환전류밀도가 큰 것과 관계된다.This is related to the large hydrogen overvoltage of zinc and the high exchange current density for hydrogen evolution.
즉, 아연이 소지철보다 낮은 전위를 가지고 있어서 양극으로 작용하기 때문에 갈바닉 전류는 아연 도금층에서 소지철로 흐르게 되며 그 결과 소지철은 음극 보호된다.That is, since zinc has a potential lower than that of ferrous iron, it acts as an anode, so that galvanic current flows from the zinc plated layer to the refractory iron, and the resulting iron is cathodically protected.
그러나 아연도금층은 대기중에 습도가 높을 때 오랜시간이 지나면 아연도금층 표면이 백색으로 부식되는 백청이 발생되고 아연도금층의 부식생성물인 백청이 진전되게 되면 아연의 희생방식성이 저하되므로 결국 소지철의 부식생성물인 적청을 발생시키게 되므로 용융아연 도금층의 내식성의 향상이 절실히 요구되고 있다.However, when the humidity of the galvanized layer is high, the white surface of the zinc plated layer is corroded to white when a long time passes, and when the white rust which is a corrosion product of the zinc plated layer advances, the sacrificial corrosion resistance of the zinc is lowered. It is required to improve the corrosion resistance of the hot-dip galvanized layer because it causes generation of red rust which is a product.
이와같은 이유로 지금까지 용융아연 도금강판의 내식성을 개선시키는 데 사용되고있는 방법으로써 아연도금층의 두께를 증가시키는 방법은 소지철에 대한 앙연 도금층의 보호작용을 향상시키지만 필요이상의 도금부착량 증가는 표면품질을 저해할 뿐만 아니라 경제적으로도 바람직하지 못하며 두꺼운 도금강판을 가공할 때 도금층이 균열되어 벗겨져 외관을 해치는 결과를 초래하며, 현재 가장 일반적으로 사용되는 도금층 표면에 부가적으로 크로메이트 피막을 형성시키는 방법은 일본 특개평 5-295593호와 같이 내식성을 향상시키기 위하여 실리카겔 등을 함유하는 크롬산 용액에 침적하는 크로메이트 처리방법은 내식성을 상당히 개선시킬 수 있으나 염수분무시험에 의한 최대 백청발생 지연시간이 120시간 이하로 충분하지 못함은 물론 다공정으로 생산성을 저하시키며, 제조비용을 높이게 되고 크롬용액은 중금속으로 환경오염에도 큰 문제를 가지고 있다.For this reason, the method of increasing the thickness of the zinc plated layer to improve the corrosion resistance of the hot-dip galvanized steel sheet up to now improves the protective effect of the silver plated layer on the iron core, And it is economically undesirable. When a thick plate is processed, the plating layer is cracked and peeled off, resulting in deterioration of the appearance. In addition, a method of forming an additional passive film on the surface of the most commonly used plating layer is disclosed in Japanese Patent Application Laid- The chromate treatment method of immersing in a chromic acid solution containing silica gel or the like to improve the corrosion resistance as shown in Japanese Patent Laid-Open No. 5-295593 can significantly improve the corrosion resistance, but the maximum white stone generation delay time by the salt spray test is not more than 120 hours Not to mention, The productivity is lowered, the manufacturing cost is increased, and the chromium solution is a heavy metal, which is a big problem in environmental pollution.
또한, 도금욕에 다른 합금원소를 첨가하여 아연도금층 자체의 질을 개선하는 방법은 도금층이 얇으면서 내식성을 향상시키는 가장 경제적인 방법이다.Further, a method of improving the quality of the zinc plated layer itself by adding other alloying elements to the plating bath is the most economical method for improving the corrosion resistance with the thin plating layer.
예를 들면 미국특허 제 4,027,478호에서는 0.2∼17wt.% AL, 0.03∼0.15wt.% Mg, 잔부 아연 및 불순물로 구성된 아연욕을 사용하여 통상적인 도금조건에서 도금하는 것에 의해서 용융아연 도금강판 대비 2∼3배의 내식성 향상을 가져온다고 한다.For example, in U.S. Patent No. 4,027,478, a zinc bath composed of 0.2 to 17 wt.% AL, 0.03 to 0.15 wt.% Mg, balance zinc and impurities is used to coat 2 To 3 times the corrosion resistance.
그러나 내식성 향상을 위해서 첨가되는 합금원소인 Al, Mg 및 Cu 등을 단독 또는 복합적으로 첨가하고 있으며, 이 합금원소의 첨가 범위 및 내식성 향상 정도가 발명자에 따라 크게 차이가 있고, Cu 첨가시에는 도금부착량은 감소하나 대기부식성은 개선되는 것으로 알려져 있다.However, Al, Mg and Cu, which are added for the purpose of improving the corrosion resistance, are added singly or in combination, and the range of addition of the alloying element and degree of improvement in corrosion resistance are greatly different according to the inventors. Is reduced but atmospheric corrosion is improved.
상기와 같이 지금까지 알려진 도금욕 합금원소 첨가에 의한 내식성 향상은 기존의 용융아연 도금강판 대비 2∼3배의 내식성 향상이 대부분이다.As described above, improvement in corrosion resistance by the addition of a plating bath alloying element as known so far is mostly two to three times as much as the improvement in corrosion resistance of a conventional hot-dip galvanized steel sheet.
따라서 도금후 부가적으로 크로메이트 처리를 실시하여야 하는 문제점이 있다.Therefore, there is a problem that chromate treatment must be additionally performed after plating.
상기와 같은 문제점을 해결하기 위하여 본 발명은 도금욕에 합금원소를 첨가하여 도금하는 것만으로도 충분한 내식성의 향상 효과를 얻기 위하여 아연합금계 및 후처리 방법을 연구하여 아연-망간 합금계를 도금성분으로 하는 도금욕에서 도금 처리한 후 자연냉각시켜 도금층 표면에 부동태 피막인 산화망간 피막을 형성시키므로서 용융아연 도금강판의 내식성을 향상시키는 표면형상 및 내식성이 우수한 용융아연 도금강판 제조방법을 제공하는 것을 그 목적으로 한다.In order to solve the above-mentioned problems, the present invention has been studied to obtain a sufficient corrosion resistance improvement effect by simply adding an alloy element to a plating bath and plating, and a zinc-manganese alloy system is studied as a plating component And a method of manufacturing a hot dip galvanized steel sheet having excellent surface shape and corrosion resistance by forming a manganese oxide film as a passive film on the surface of a plated layer to improve the corrosion resistance of the hot dip galvanized steel sheet It is for that purpose.
도 1은 도금욕에 첨가되는 합금원소 Mn 농도변화에 따른 양극분극시험선도이다.Fig. 1 is a diagram of a bipolar polarization test according to a change in an alloy element Mn concentration added to a plating bath.
상기와 같은 목적을 달성하기 위하여 본 발명은 0.3∼0.5wt.% Mn이 첨가된 아연합금계를 도금욕 성분계로 하고 이러한 성분계가 475∼600℃로 유지되는 도금욕에 도금소재를 침적 유지하여 도금한 후 산소분위기의 공기중에서 자연냉각하여 도금층 표면에 부동태 피막인 산화망간 피막을 형성시키는 표면형상 및 내식성이 우수한 용융아연 도금강판 제조방법을 제공한다.In order to accomplish the above object, the present invention provides a method of manufacturing a plating bath, comprising the steps of: forming a plating bath component with 0.3 to 0.5 wt.% Mn added thereto and maintaining the plating solution at 475 to 600 DEG C, There is provided a method for manufacturing a hot dip galvanized steel sheet excellent in surface shape and corrosion resistance, wherein the hot rolled steel sheet is naturally cooled in air in an oxygen atmosphere to form a manganese oxide film as a passive film on the surface of the plated layer.
이하, 본 발명을 보다 상세하게 설명한다.Hereinafter, the present invention will be described in more detail.
상기와 같은 용융아연 도금강판의 내식성을 향상시키기 위한 도금욕 첨가원소로 Mn을 첨가하는 이유는 Mn의 전극전위(-1.06V)가 Zn의 전극전위(-0.76V)보다 비하기 때문에 통상적으로 첨가되는 범위(0.1∼20wt.%)의 합금상태에서는 순수한 아연 대비 내식성이 열화되나 Mn은 공기중에서 산화가 용이하기 때문에 도금층 표면에 산화망간인 MnO를 형성하게 된다.The reason for adding Mn to the plating bath additive element for improving the corrosion resistance of the hot-dip galvanized steel sheet is that since the Mn electrode potential (-1.06 V) is higher than the Zn electrode potential (-0.76 V) (0.1 to 20 wt.%), The corrosion resistance of pure zinc deteriorates. However, since Mn is easily oxidized in the air, MnO, which is manganese oxide, forms on the surface of the plating layer.
이 도금층 표면의 산화망간 피막은 부동태화 작용을 나타내므로 아연의 부식생성물이 ZnO로 변화되지 않고 Zn(OH)2로 존재하기 쉽다.Since the manganese oxide film on the surface of the plating layer shows a passivating action, the corrosion product of zinc is not converted into ZnO and is likely to exist as Zn (OH) 2 .
이 Zn(OH)2는 안정한 피막으로 부식반응에서 음극반응인 산화환원반응을 억제하여 내식성의 향상을 가져오기 때문에 Mn을 도금욕 첨가원소로 하였다.Since Zn (OH) 2 is a stable coating, it inhibits oxidation reaction which is negative reaction in the corrosion reaction and improves corrosion resistance. Therefore, Mn is added to the plating bath additive element.
그러나, 이와같은 도금욕의 Mn 첨가효과가 모든 조건에서 일어나는 것은 아니다.However, the Mn addition effect of such a plating bath does not occur under all conditions.
이하, 본 발명의 수치한정에 대하여 설명한다.Hereinafter, the numerical limitations of the present invention will be described.
도금욕에 첨가되는 Mn의 첨가량이 0.3wt.% 이하에서는 산화망간 피막의 형서이 매우 느리기 때문에 산화피막이 불균일하고 얇게 되어 내식성 향상을 가져오지 못하게 된다.When the addition amount of Mn added to the plating bath is 0.3 wt.% Or less, the manganese oxide coating is very slow in shape, so that the oxide coating is uneven and thin and the corrosion resistance is not improved.
실례로 도 1과 같이 도금욕의 Mn함유량 변화에 따른 양극 분극곡선에 의하면 Mn 첨가량이 0.3wt.%이하에서는 산화피막의 불균일로 부식속도를 나타내는 부식전류가 0.772A/㎠으로 균일하게 산화피막 형성되는 0.3∼0.5wt.% Mn 첨가강의 0.1A/㎠보다 매우 크므로 내식성 저하가 초래됨을 볼 수 있다.For example, as shown in Fig. 1, according to the anodic polarization curve according to the Mn content change of the plating bath, when the Mn addition amount is 0.3 wt.% Or less, the corrosion current indicating the corrosion rate due to the unevenness of the oxide film is 0.772 A / % Mn added steel of 0.1 A / cm < 2 >, which results in a decrease in corrosion resistance.
이에 반하여 Mn 함량이 0.5wt.% 이상이 되면 드로스 발생이 많아져서 젖음성을 저해시키므로 미도금 발생 및 망간 산화피막이 불균일하게 형성되어 국부적인 내식성 저하을 초래하므로 바람직하지 않다.On the contrary, when the Mn content is more than 0.5 wt.%, The occurrence of dross is increased and the wettability is inhibited. Therefore, undoped plating and manganese oxide coating are unevenly formed, which leads to local corrosion resistance deterioration.
한편, 상기와 같은 도금욕의 성분계에서 도금한 도금층 표면에 균일하고 두꺼운 산화망간피막을이 형성시키기 위해서는 475∼600℃ 의 도금욕 온도를 유지시켜 도금욕의 유동성 미치 젖음성을 확보해야 하는데 그 이유는 475℃이하에서는 유동성 및 젖음성 저하로 도금층 표면에 드로스 부착 및 미도금이 발생하여 국부적으로 내석성 저하를 가져온다.Meanwhile, in order to form a uniform and thick manganese oxide coating on the surface of the plated layer in the component system of the plating bath as described above, it is necessary to maintain the plating bath temperature of 475 to 600 ° C to secure the fluidity and wettability of the plating bath. When the temperature is lower than 475 ° C, there is a problem of droplet adhesion and non-plating on the surface of the plated layer due to a decrease in fluidity and wettability, resulting in a decrease in abrasion resistance locally.
또한, 600℃ 이상의 도금욕에서는 Mn 이 산화되기 용이한 원소이기 때문에 도금욕 표면에서의 과다한 산화물 형성 및 도금층 표면의 드로스부착이 증가하여 도금층 표면외관을 저해하게 되며, 도금후 도금층 표면에서서의 산화피막형성은 빠르나 도금층 내부에서는 잠열에 의해서 용융상태를 유지하기 때문에 도금층 표면이 흘려내려 표면에 주름이 잡혀서 표면외관을 저해할 뿐만 아니라 이러한 요철부의 산화피막 두께차로 내식성 차를 유발하고 두께가 얇고 불균일한 부분의 내식성 저하를 초래하게 된다.In addition, in the plating bath of 600 占 폚 or more, since Mn is an element which is easily oxidized, excessive oxide formation on the surface of the plating bath and adhesion of dross on the surface of the plating layer are increased to deteriorate the appearance of the surface of the plating layer. The oxidation film formation is fast, but the molten state is maintained in the plating layer due to the latent heat. Therefore, the surface of the plating layer flows down and wrinkles are formed on the surface, which not only hinders the appearance of the surface but also induces a corrosion resistance difference by the difference in thickness of the oxide film. The corrosion resistance of one portion is lowered.
이러한 현상은 산화가 촉진되는 높은 Mn 함유 도금욕과 높은 도금욕 온도에의해 발생하게 된다.This phenomenon is caused by a high Mn-containing plating bath and a high plating bath temperature, in which oxidation is promoted.
상기와 같은 본 발명의 도금욕 온도는 통상의 용융아연 도금강판의 도금욕 온도보다 높은 온도이기 때문에 도금후 산소분위기에서 자연냉각으로도 충분히 균일하고 두꺼운 산화피막 형성이 가능하므로 도금후 후처리 방법은 산소분위기의 자연냉각으로 한다.Since the plating bath temperature of the present invention as described above is higher than the plating bath temperature of a conventional hot-dip galvanized steel sheet, a sufficiently uniform and thick oxide film can be formed even by natural cooling in an oxygen atmosphere after plating, It is natural cooling in an oxygen atmosphere.
이하 실시예와 함께 본 발명을 보다 상세히 설명한다.The present invention will be described in more detail with reference to the following examples.
실시예Example
두께가 0.8㎜인 일반 저탄소강의 냉연강판을 가로 100㎜, 세로 200㎜로 절단하여 시험편으로 하였다.A cold-rolled steel sheet of general low-carbon steel having a thickness of 0.8 mm was cut into a width of 100 mm and a length of 200 mm.
이 시험편을 알카리 용액에서 침적하여 탈지한 후 750℃의 소둔환원온도에서 열처리하였다.This specimen was degreased by immersion in an alkali solution, and then heat-treated at a temperature of annealing at 750 ° C.
이렇게 전처리된 도금소재를 표 1과 같은 도금욕 조성에서 도금욕 온도 450∼650℃로 1∼3초간 침적하여 단면 도금부착량이 150g/㎥되게 도금한 후 공기중에서 자연냉각하여 도금층 표면에 산화망간피막이 형성된 용융아연 도금강판을 제조하였다.The pretreated plating material was immersed in a plating bath composition as shown in Table 1 for 1 to 3 seconds at a plating bath temperature of 450 to 650 ° C to deposit 150 g / m 3 of the plating amount of one side of the plating layer and naturally cooled in air to form a manganese oxide coating To prepare a hot-dip galvanized steel sheet.
이렇게 제조된 용융아연 도금강판의 드로스 발생 및 미도금 발생 유무를 육안으로 관찰하였으며, 내식성 평가는 야극분극실험 및 염수분무 시험법으로 하였다.Dust generation and non - plating occurrence of the hot - dip galvanized steel sheet thus produced were visually observed, and corrosion resistance was evaluated by night polarization test and salt spray test.
양극분극실험은 기준전지를 감흥전지로 하고 전해용액은 3.5% NaCl 용액에서 부가전위에 따른 전류밀도 변화를 측정하여 부식전위 및 부식전류밀도를 구하였다.In the anodic polarization test, the corrosion potential and the corrosion current density were determined by measuring the change in current density according to the added potential in the reference cell as an inspiration cell and the electrolytic solution in a 3.5% NaCl solution.
여기서 음극반응은 도금욕 성분 및 도금욕 온도변화에 따른 부식전위 및 부식전류 밀도의 변화가 없기 때문에 제외하였다.The negative electrode reaction was excluded because there was no change in corrosion potential and corrosion current density with changes in plating bath component and plating bath temperature.
따라서 부식전류값은 -0.8V 의 부가전위에서의 전류밀도값으로 하였고, 염수분무시험은 JIS Z2371 규정에 따라 실시하였으며, 이 때 내식성 평가는 아연 부식생성물인 백청이 100% 발생할 시점까지 걸리는 시간으로 하였다.Therefore, the corrosion current value was taken as the current density value at -0.8 V and the salt spray test was carried out in accordance with JIS Z2371, and the corrosion resistance was evaluated as the time taken for 100% Respectively.
표 1.Table 1.
○ : 양호, × : 불량O: Good, X: Bad
* 부식전류밀도 : 부가전위 -0.8V에서의 전류밀도* Corrosion current density: current density at an additional potential of -0.8 V
내식성의 평가기준은 용융아연 도금강판의 나내식성이 300시간 이상을 만족하는 경우로 하였으며 그 결과를 표 1에 나타내었다.The evaluation criteria of the corrosion resistance are as follows. The corrosion resistance of the hot-dip galvanized steel sheet satisfies 300 hours or more. The results are shown in Table 1.
표 1에서 나타낸 바와 같이 본 발명의 경우인 0.3∼0.5wt.% Mn-Zn계 도금욕에서 475∼600℃의 도금욕 온도로 도금한 후 공기중에서 자연냉각한 경우는 부식전위가 -975V 이상으로 통상적인 용융아연 도금강판의 부식전위 및 0.1∼0.5wt.% Ti-Zn계 도금욕으로 도금한 후 자연냉각한 경우의 부식전위보다 귀한 전위를 나타내므로 염수분무시험결과 백청발생시간이 330∼600시간으로 내식성이 종래의 용융아연 도금강판 및 Ti-Zn계 용융아연 도금강판에 비하여 10∼20배 이상 크게 향상되었다.As shown in Table 1, when plating was carried out at a plating bath temperature of 475 to 600 ° C in a 0.3 to 0.5 wt.% Mn-Zn based plating bath in the case of the present invention and then naturally cooled in air, the corrosion potential was increased to -975 V or more Since the corrosion potential of a conventional hot-dip galvanized steel sheet and the galvanic potential when it is naturally cooled after plated with a 0.1-0.5 wt.% Ti-Zn system bath are exhibited, the time of occurrence of white rust is 330 to 600 The corrosion resistance was improved 10 to 20 times or more as compared with the conventional hot-dip galvanized steel sheet and the Ti-Zn based hot-dip galvanized steel sheet.
이에 반해 도금욕에 첨가되는 Mn의 함유량이 0.3wt.% 이하인 경우는 드로스부착 및 미도금 발생에 의한 도금층 표면의 불균일한 산화피막 형성으로 내식성을 충분히 확보하는 것이 불가능하였고, 0.1∼0.5 wt.% Ti-Zn계 도금욕으로 도금한 후 자연냉각한 경우는 부식전위가 통상적인 용융아연 도금강판과 유사하나 부식전류밀도가 낮으므로 부식속도가 감소하여 내식성은 다소 개선할 수 있으나, 충분하지 못한 관계로 추가적으로 크로메이트 처리 등의 후처리가 필요하다.On the contrary, when the content of Mn added to the plating bath is 0.3 wt.% Or less, it is impossible to sufficiently secure the corrosion resistance due to the formation of a non-uniform oxide film on the surface of the plating layer due to the adhesion of dross and occurrence of unplating. In the case of natural cooling after plating with a Ti-Zn based plating bath, the corrosion potential is similar to that of a conventional hot-dip galvanized steel sheet, but since the corrosion current density is low, the corrosion rate is reduced and the corrosion resistance can be somewhat improved, In addition, post-treatment such as chromate treatment is necessary.
또한, 도금욕 온도가 본 발명의 기준인 475∼600℃를 벗어나는 경우는 유동성 저하, 드로스 부착 및 미도금 발생으로 표면 외관이 불량하고 도금층 표면의 산화피막 형성이 불균일하여 내식성 확보가 불가능하다.In addition, when the plating bath temperature is outside the range of 475 to 600 占 폚 according to the present invention, the surface appearance is poor due to deterioration of fluidity, dross adhesion, and unplated formation, and formation of an oxide film on the surface of the plating layer is uneven.
0.3∼0.5wt.% Mn-Zn계 도금욕에서 475∼600℃의 도금욕 온도로 도금한 후 공기중에서 자연냉각하는 것에 의한 표면의 산화피막형성으로 도금강판의 내식성을 크게 향상시켜 도금 부착량의 증대 및 추가의 크로메이트 처리가 필요 없어 경제적이며, 불필요한 공정의 제거로 생산성을 향상시키는 효과를 제공한다.The plating is carried out at a plating bath temperature of 475 to 600 ° C in a 0.3 to 0.5 wt.% Mn-Zn plating bath and then naturally cooled in air to form an oxide film on the surface, thereby greatly increasing the corrosion resistance of the coated steel sheet, And an additional chromate treatment is not required, which is economical and provides an effect of improving productivity by eliminating unnecessary processes.
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| CN114086094A (en) * | 2021-11-19 | 2022-02-25 | 湖南杭德通讯有限公司 | Hot galvanizing process for metal fastener |
| CN114086093A (en) * | 2021-11-19 | 2022-02-25 | 湖南杭德通讯有限公司 | Galvanizing treatment process for urban intelligent traffic pole |
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| WO2021125525A1 (en) * | 2019-12-17 | 2021-06-24 | 주식회사 포스코 | High-strength cold-rolled steel sheet having excellent phosphatability and manufacturing method therefor |
| KR20210077292A (en) * | 2019-12-17 | 2021-06-25 | 주식회사 포스코 | High strength cold steel sheet with good phosphating property and method for manufacturing the same |
| CN114086094A (en) * | 2021-11-19 | 2022-02-25 | 湖南杭德通讯有限公司 | Hot galvanizing process for metal fastener |
| CN114086093A (en) * | 2021-11-19 | 2022-02-25 | 湖南杭德通讯有限公司 | Galvanizing treatment process for urban intelligent traffic pole |
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