JP2014189805A - Zinc-plated cold rolled steel plate - Google Patents
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- JP2014189805A JP2014189805A JP2013063603A JP2013063603A JP2014189805A JP 2014189805 A JP2014189805 A JP 2014189805A JP 2013063603 A JP2013063603 A JP 2013063603A JP 2013063603 A JP2013063603 A JP 2013063603A JP 2014189805 A JP2014189805 A JP 2014189805A
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- 239000010960 cold rolled steel Substances 0.000 title claims abstract description 60
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 105
- 239000010959 steel Substances 0.000 claims abstract description 105
- 239000011701 zinc Substances 0.000 claims abstract description 104
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims abstract description 44
- 229910052725 zinc Inorganic materials 0.000 claims abstract description 44
- 238000009713 electroplating Methods 0.000 claims abstract description 34
- 229910052751 metal Inorganic materials 0.000 claims description 28
- 239000002184 metal Substances 0.000 claims description 28
- 229910052748 manganese Inorganic materials 0.000 claims description 6
- 229910052814 silicon oxide Inorganic materials 0.000 claims description 3
- 239000000126 substance Substances 0.000 abstract description 67
- 239000000463 material Substances 0.000 abstract description 6
- 229910045601 alloy Inorganic materials 0.000 abstract description 5
- 239000000956 alloy Substances 0.000 abstract description 5
- 238000006243 chemical reaction Methods 0.000 description 64
- 239000013078 crystal Substances 0.000 description 22
- 238000000034 method Methods 0.000 description 21
- 238000000137 annealing Methods 0.000 description 13
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- 239000011248 coating agent Substances 0.000 description 11
- 230000000694 effects Effects 0.000 description 9
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- 229910019142 PO4 Inorganic materials 0.000 description 7
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 7
- 239000010452 phosphate Substances 0.000 description 7
- 239000000243 solution Substances 0.000 description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 6
- 229910004298 SiO 2 Inorganic materials 0.000 description 6
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 6
- 230000007797 corrosion Effects 0.000 description 6
- 238000005260 corrosion Methods 0.000 description 6
- 229910052710 silicon Inorganic materials 0.000 description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 239000012298 atmosphere Substances 0.000 description 5
- 238000011156 evaluation Methods 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 5
- 238000005554 pickling Methods 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- 238000007739 conversion coating Methods 0.000 description 4
- 238000005238 degreasing Methods 0.000 description 4
- 150000003839 salts Chemical class 0.000 description 4
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 3
- 239000003929 acidic solution Substances 0.000 description 3
- 239000003513 alkali Substances 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- 239000002131 composite material Substances 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 238000007654 immersion Methods 0.000 description 3
- 230000006872 improvement Effects 0.000 description 3
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- 229910018643 Mn—Si Inorganic materials 0.000 description 2
- 229910006639 Si—Mn Inorganic materials 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
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- 238000004453 electron probe microanalysis Methods 0.000 description 2
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- 238000000227 grinding Methods 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- VASIZKWUTCETSD-UHFFFAOYSA-N manganese(II) oxide Inorganic materials [Mn]=O VASIZKWUTCETSD-UHFFFAOYSA-N 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
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- 230000006911 nucleation Effects 0.000 description 2
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- 229910052827 phosphophyllite Inorganic materials 0.000 description 2
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- 239000002253 acid Substances 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 239000012267 brine Substances 0.000 description 1
- 238000011088 calibration curve Methods 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 238000012790 confirmation Methods 0.000 description 1
- HTXDPTMKBJXEOW-UHFFFAOYSA-N dioxoiridium Chemical compound O=[Ir]=O HTXDPTMKBJXEOW-UHFFFAOYSA-N 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000005868 electrolysis reaction Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000005246 galvanizing Methods 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 230000005764 inhibitory process Effects 0.000 description 1
- 238000010884 ion-beam technique Methods 0.000 description 1
- 229910000457 iridium oxide Inorganic materials 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 229910000734 martensite Inorganic materials 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
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- 230000001105 regulatory effect Effects 0.000 description 1
- 238000003303 reheating Methods 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 230000008719 thickening Effects 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
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- RZLVQBNCHSJZPX-UHFFFAOYSA-L zinc sulfate heptahydrate Chemical compound O.O.O.O.O.O.O.[Zn+2].[O-]S([O-])(=O)=O RZLVQBNCHSJZPX-UHFFFAOYSA-L 0.000 description 1
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- Electroplating Methods And Accessories (AREA)
- Chemical Treatment Of Metals (AREA)
- Heat Treatment Of Sheet Steel (AREA)
- Other Surface Treatments For Metallic Materials (AREA)
Abstract
Description
本発明は、自動車ボディ用途に使用される亜鉛めっき冷延鋼板に対しても、塗装前処理工程において良好な化成皮膜が形成され、かつ塗装後の耐食性についても良好である亜鉛めっき冷延鋼板に関するものである。 The present invention relates to a galvanized cold-rolled steel sheet that has a good chemical conversion film formed in the pre-painting treatment process and has good corrosion resistance after painting, even for galvanized cold-rolled steel sheets used for automobile body applications. Is.
近年、地球温暖化対策として、自動車からのＣＯ２排出量を減らすために、車体の軽量化をいかに行うかが自動車メーカーにとって課題となっている。車体の軽量化に対しては、使用する鋼板の薄肉化が最も有効であるが、鋼板の強度が同じままで板厚だけを薄くすると、鋼板の剛性が減少し、衝突時などの乗員の安全性を確保できなくなる。このため、板厚を薄くし、その分で減った剛性を鋼の高強度化により補った、高強度鋼板を車体材料として採用する場合がある。特に最近では、引張強度１１８０ＭＰａクラスの高強度鋼板を自動車ボディ用途に使用する動きが活発になってきている。 In recent years, as a measure against global warming, how to reduce the weight of the vehicle body in order to reduce CO 2 emissions from automobiles has become a challenge for automobile manufacturers. Thinning the steel plate used is most effective for reducing the weight of the vehicle body, but reducing the thickness of the steel plate while keeping the strength of the steel plate the same will reduce the rigidity of the steel plate and improve occupant safety in the event of a collision. It becomes impossible to secure the sex. For this reason, there is a case where a high-strength steel plate, in which the plate thickness is reduced and the rigidity reduced by that amount is compensated by increasing the strength of the steel, is used as the vehicle body material. In particular, recently, there has been an active movement to use high-strength steel sheets having a tensile strength of 1180 MPa class for automobile body applications.
鋼板を高強度化するには、ＳｉやＭｎなどの合金元素を添加して固溶強化したり結晶粒を微細化したりする方法や、Ｎｂ、Ｔｉ、Ｖなどの析出物形成元素を添加して析出強化する方法、マルテンサイト相などの硬質な変態組織を生成させて強化する方法などが有効である。 In order to increase the strength of steel sheets, alloy elements such as Si and Mn are added to strengthen the solution or refine crystal grains, and precipitate forming elements such as Nb, Ti, and V are added. Effective methods include precipitation strengthening and a method of strengthening by generating a hard transformation structure such as a martensite phase.
一般に合金元素の添加による高強度化は、延性の低下を招く場合があるため、部品の形状をつくるプレス成形がしにくいという欠点がある。しかし、Ｓｉは他の元素と比較して延性低下の影響が小さいことから、延性を確保しつつ高強度化を図る際には有効な元素である。このため、加工性と高強度化を両立した鋼板にはＳｉの添加がほぼ必須である。 In general, increasing the strength by adding an alloying element may cause a decrease in ductility, so that there is a drawback that it is difficult to perform press forming to form the shape of a part. However, since Si is less affected by the reduction in ductility than other elements, Si is an effective element for increasing the strength while ensuring ductility. For this reason, it is almost essential to add Si to a steel sheet that achieves both workability and high strength.
上記の通り、Ｓｉは有効な元素の一つであるが、Ｓｉは酸化物の平衡酸素分圧が非常に低く、一般の冷延鋼板の製造で使用される連続焼鈍炉内の還元性雰囲気においても容易に酸化される。このことから、Ｓｉを含有した鋼板を連続焼鈍炉に通板すると、Ｓｉが鋼板表面で選択酸化されＳｉＯ２が形成される。このように表面にＳｉＯ２が形成された鋼板を塗装前の化成処理に供すると、このＳｉＯ２が化成処理液と鋼板の反応を阻害する。その結果、処理後の鋼板表面に、化成結晶が形成されない所謂スケと呼ばれる部分が生じてしまう。このように化成処理後にスケが存在する鋼板は、化成処理後の水洗段階で既に錆が見られることがある。また、仮に錆にまで至らなかったとしても、電着塗装後の鋼板の耐食性が非常に悪いことから、Ｓｉを含有する高強度冷延鋼板を自動車ボディ用途に使用することは困難であった。 As described above, Si is one of the effective elements, but Si has a very low equilibrium oxygen partial pressure of the oxide, and in a reducing atmosphere in a continuous annealing furnace used in the production of general cold-rolled steel sheets. Are also easily oxidized. For this reason, when a steel sheet containing Si is passed through a continuous annealing furnace, Si is selectively oxidized on the surface of the steel sheet to form SiO 2 . When the steel plate with SiO 2 formed on the surface in this way is subjected to a chemical conversion treatment before coating, the SiO 2 inhibits the reaction between the chemical conversion solution and the steel plate. As a result, a so-called skein where no conversion crystal is formed is formed on the surface of the steel sheet after the treatment. As described above, the steel sheet in which the scale is present after the chemical conversion treatment may already have rust in the water washing stage after the chemical conversion treatment. Moreover, even if it did not reach rust, it was difficult to use a high-strength cold-rolled steel sheet containing Si for automobile body use because the corrosion resistance of the steel sheet after electrodeposition coating was very poor.
このようなＳｉを含有する高強度冷延鋼板の化成処理性を改善する方法としては、従来から多くの提案がある。例えば、特許文献１には、原子比（Ｓｉ／Ｍｎ）が1以下の酸化物を表面に形成した冷延鋼板と、その製造方法として、鋼板成分の（Ｓｉ／Ｍｎ）比、焼鈍温度と、雰囲気の水素と水分の分圧比をパラメータとして規定したものが提案されている。しかし、この方法では、鋼板成分のＳｉ量が増加するにつれて、焼鈍温度を低下させる必要がある。また、所望の強度や延びを得るために高温焼鈍が必要な場合には、雰囲気の水分比を上げることで達成できるが、このとき鋼板表面にはＦｅ系酸化物が形成されるため、製品として成立しない。すなわち、特許文献１に記載の技術は、現在の高強度鋼板の主流である１．０％程度のＳｉを含有する鋼板に対しては適用できない。 Conventionally, there are many proposals for improving the chemical conversion processability of such a high-strength cold-rolled steel sheet containing Si. For example, in Patent Document 1, a cold-rolled steel sheet having an oxide with an atomic ratio (Si / Mn) of 1 or less formed on the surface, and a manufacturing method thereof, (Si / Mn) ratio of steel sheet components, annealing temperature, The thing which prescribed | regulated the partial pressure ratio of the hydrogen of the atmosphere and a water | moisture content as a parameter is proposed. However, in this method, it is necessary to lower the annealing temperature as the amount of Si in the steel plate component increases. In addition, when high temperature annealing is required to obtain the desired strength and elongation, it can be achieved by increasing the moisture ratio of the atmosphere. Not satisfied. That is, the technique described in Patent Document 1 cannot be applied to a steel sheet containing about 1.0% Si, which is the mainstream of current high-strength steel sheets.
特許文献２には、Ｓｉ含有量が０．０５〜２％、かつ（Ｓｉ）／（Ｍｎ）≦０．４の鋼板に対して、鋼板表面のＳｉ−Ｍｎ複合酸化物のサイズと単位面積あたりの個数、かつＳｉを主体とする酸化物の鋼板表面被覆率を規定した高強度冷延鋼板が提案されている。また、特許文献３には、Ｓｉ含有量が０．１〜１％、かつ（Ｓｉ）／（Ｍｎ）≦０．４の鋼板に対して、鋼板表面のＭｎ−Ｓｉ複合酸化物の（Ｍｎ／Ｓｉ）比とサイズと単位面積あたりの個数、かつＳｉを主体とする酸化物の鋼板表面被覆率を規定した高強度冷延鋼板が提案されている。さらに、特許文献４には、Ｓｉ含有量が０．１〜２％、かつ（Ｓｉ）／（Ｍｎ）≦０．４の鋼板に対して、鋼板表面のＭｎ−Ｓｉ複合酸化物の（Ｍｎ／Ｓｉ）比とサイズと単位面積あたりの個数、かつＳｉを主体とする酸化物の鋼板表面被覆率を規定した高強度冷延鋼板が提案されている。これらは、最大２％のＳｉを含有する鋼板に対してまで成立し、その製法例としては、熱間圧延後の酸洗条件や連続焼鈍時の露点を−４０℃以下に抑えることを提示している。しかし、これらは、そもそもの前提としてＳｉ／Ｍｎ比を満足する鋼板であることが必要であり、鋼板成分の自由度が少ない欠点がある。また、連続焼鈍時の露点を−４０℃以下とすることは現実の製造ラインの露点変動を考えるとかなり制御が困難である。したがって、特許文献２〜４に記載の技術は量産には適さない。 In Patent Document 2, the size of Si-Mn composite oxide on the surface of the steel sheet and the unit area per steel sheet with a Si content of 0.05-2% and (Si) / (Mn) ≦ 0.4. A high-strength cold-rolled steel sheet has been proposed that defines the number of the steel sheets and the surface coverage of an oxide steel sheet mainly composed of Si. Patent Document 3 discloses that the Mn-Si complex oxide (Mn / Si) on the surface of the steel sheet has a Si content of 0.1 to 1% and (Si) / (Mn) ≦ 0.4. A high-strength cold-rolled steel sheet has been proposed in which the ratio of Si), the size, the number per unit area, and the surface coverage of an oxide-based steel sheet are defined. Further, in Patent Document 4, the Mn—Si composite oxide (Mn / Si) on the steel sheet surface is compared with the steel sheet having a Si content of 0.1 to 2% and (Si) / (Mn) ≦ 0.4. A high-strength cold-rolled steel sheet has been proposed in which the ratio of Si), the size, the number per unit area, and the surface coverage of an oxide-based steel sheet are defined. These hold even for steel sheets containing up to 2% Si, and as an example of the production method, it is proposed that the pickling conditions after hot rolling and the dew point during continuous annealing be suppressed to -40 ° C or lower. ing. However, these are required to be steel sheets that satisfy the Si / Mn ratio as a premise, and have a drawback that the degree of freedom of the steel sheet components is small. Moreover, it is considerably difficult to control the dew point at -40 ° C. or lower during continuous annealing in consideration of the dew point fluctuation of an actual production line. Therefore, the techniques described in Patent Documents 2 to 4 are not suitable for mass production.
特許文献５には、Ｓｉ含有量が０．４％以上、かつ（Ｓｉ）／（Ｍｎ）≧０．４の鋼板に対して、鋼板表面のＳｉ基酸化物の表面被覆率を規定した冷延鋼板と、焼鈍後に酸洗を施す製造方法が提案されている。また、特許文献６には、Ｓｉを０．５質量%以上含有する鋼板に対して、焼鈍後に鋼板表面を２．０ｇ／ｍ２以上研削する技術が提案されている。さらに、特許文献７には、Ｓｉを０．５〜２．０％含有する鋼板を焼鈍した後に、ｐＨが０〜４、温度が１０〜１００℃の酸性溶液で５〜１５０秒間処理し、かつｐＨが１０〜１４、温度が１０〜１００℃のアルカリ溶液で２〜５０秒間処理を行う技術が提案されている。これらは、いずれも焼鈍後の表面に形成された酸化物皮膜を除去するものである。特許文献５の例では、Ｓｉ系酸化物を除去するために高濃度の酸を使用する必要があり、この場合、逆に鉄地の不働態皮膜の形成を促進するため、必ずしも化成処理性の向上には働かない欠点がある。また、特許文献６や７では、ライン内に、研削のセクション、もしくは酸性溶液処理に続いてアルカリ溶液処理を行うセクションを設ける必要があり、設備の長大化やコストの増加を招き、現実的ではない。 Patent Document 5 discloses cold rolling in which the surface coverage of the Si-based oxide on the steel sheet surface is specified for a steel sheet having a Si content of 0.4% or more and (Si) / (Mn) ≧ 0.4. A steel plate and a manufacturing method for pickling after annealing have been proposed. Patent Document 6 proposes a technique for grinding a steel plate surface by 2.0 g / m 2 or more after annealing with respect to a steel plate containing 0.5 mass% or more of Si. Furthermore, in Patent Document 7, after annealing a steel sheet containing 0.5 to 2.0% of Si, it is treated with an acidic solution having a pH of 0 to 4 and a temperature of 10 to 100 ° C. for 5 to 150 seconds, and A technique has been proposed in which treatment is performed for 2 to 50 seconds with an alkaline solution having a pH of 10 to 14 and a temperature of 10 to 100 ° C. These all remove the oxide film formed on the surface after annealing. In the example of Patent Document 5, it is necessary to use a high-concentration acid in order to remove the Si-based oxide. In this case, in order to promote the formation of a passive state film on iron, There is a drawback that does not work for improvement. In Patent Documents 6 and 7, it is necessary to provide a section for grinding or an alkaline solution treatment subsequent to an acidic solution treatment in the line, which leads to an increase in equipment length and cost. Absent.
さらに特許文献８には、鋼板表面に付着量が１０〜２０００ｍｇ／ｍ２の亜鉛めっき皮膜を有し、かつ所定の結晶配向性を持たせることで、耐型かじり性と化成処理性を両立する技術が提案されている。この技術は、主に耐型かじり性を改善するためになされたものであり、化成処理性については、わずかな亜鉛付着量においても亜鉛の付着部と鋼板露出部との間でミクロセルが形成され、化成処理反応が活発になると示唆している。しかし、鋼板のＳｉ濃度が高い場合などは、かなりの鋼板表面がＳｉＯ２酸化物で覆われており、この部分が鋼板露出部であった場合には、必ずしもミクロセルを形成するとはいえない。 Further, Patent Document 8 has both a galling resistance and a chemical conversion treatment property by having a galvanized film having an adhesion amount of 10 to 2000 mg / m 2 on the steel sheet surface and having a predetermined crystal orientation. Technology has been proposed. This technology was made mainly to improve mold galling resistance. Regarding chemical conversion treatment, even with a small amount of zinc, microcells were formed between the zinc adhesion part and the exposed steel sheet part. This suggests that the chemical conversion reaction becomes active. However, when the Si concentration of the steel plate is high, a considerable steel plate surface is covered with SiO 2 oxide, and when this portion is a steel plate exposed portion, it cannot be said that microcells are necessarily formed.
このように、充分な化成処理性を達成できないことが、高強度冷延鋼板の自動車車体への適用を阻害している。 Thus, the inability to achieve sufficient chemical conversion treatment hinders application of high-strength cold-rolled steel sheets to automobile bodies.
本発明は上記課題を解決するためになされたものであり、その目的は、鋼の加工性を維持しつつ高強度化に必要な各種合金元素の添加に対して、化成処理の観点での添加制限を抑え、強度等の確保に必要な材質と化成処理性を両立した亜鉛めっき冷延鋼板を提供することにある。 The present invention has been made in order to solve the above-mentioned problems, and its purpose is to add various alloy elements necessary for increasing the strength while maintaining the workability of steel, in terms of chemical conversion treatment. An object of the present invention is to provide a galvanized cold-rolled steel sheet that suppresses the limitation and achieves both a material necessary for securing strength and chemical conversion treatment.
ＳｉやＭｎなどを含有する冷延鋼板の表面の一部には、焼鈍後の鋼板表面に主としてＳｉ系酸化物、Ｍｎ系酸化物等から構成される不活性な酸化物皮膜が形成される。これらは非導電性物質であるため、電気めっきにより形成できる亜鉛めっきは、これらの酸化物皮膜上には形成されない。発明者らは、これらの現象について詳細な実験および解析を進め、前述した酸化物皮膜と冷延鋼板表面の間に隙間がある場合には、亜鉛めっきを電気めっきで形成する際にこの隙間に金属Ｚｎが析出し、さらに化成処理を行うと、この隙間の金属Ｚｎを起点として化成処理結晶の成長が進んでいくことを発見した。本発明はこのような知見に基づいてなされたものであり、その要旨は以下の通りである。 On part of the surface of the cold-rolled steel sheet containing Si, Mn, etc., an inactive oxide film mainly composed of Si-based oxide, Mn-based oxide, etc. is formed on the surface of the annealed steel sheet. Since these are non-conductive substances, galvanizing that can be formed by electroplating is not formed on these oxide films. The inventors have conducted detailed experiments and analyzes on these phenomena, and when there is a gap between the oxide film and the surface of the cold rolled steel sheet, the gap is formed when the zinc plating is formed by electroplating. It has been discovered that when metal Zn is deposited and further chemical conversion treatment is performed, growth of the chemical conversion treatment crystal proceeds starting from the metal Zn in the gap. This invention is made | formed based on such knowledge, The summary is as follows.
（１） 酸化物皮膜を有する亜鉛めっき冷延鋼板であって、鋼板表面に亜鉛電気めっきが形成された亜鉛電気めっき部分と、鋼板表面に酸化物皮膜が形成された酸化物皮膜部分とを備え、鋼板表面に垂直な断面を断面視したときに、前記酸化物皮膜部分は、鋼板表面と酸化物皮膜との間に隙間を有し、前記隙間の少なくとも一部に、金属Ｚｎが存在し、前記亜鉛電気めっきと前記金属Ｚｎの合計量が１００〜５０００ｍｇ／ｍ２であることを特徴とする亜鉛めっき冷延鋼板。 (1) A galvanized cold-rolled steel sheet having an oxide film, comprising: a zinc electroplated portion in which zinc electroplating is formed on the steel plate surface; and an oxide film portion in which an oxide film is formed on the steel plate surface When the cross section perpendicular to the steel sheet surface is viewed in cross section, the oxide film portion has a gap between the steel sheet surface and the oxide film, and metal Zn exists in at least a part of the gap, The galvanized cold-rolled steel sheet, wherein the total amount of the zinc electroplating and the metal Zn is 100 to 5000 mg / m 2 .
（２）鋼板表面全体に対する、前記亜鉛電気めっき部分の面積率が６０％以上であることを特徴とする（１）に記載の亜鉛めっき冷延鋼板。 (2) The galvanized cold-rolled steel sheet according to (1), wherein the area ratio of the zinc electroplated portion with respect to the entire steel sheet surface is 60% or more.
（３）前記隙間は、鋼板表面からの高さが５０〜１０００ｎｍであることを特徴とする（１）又は（２）に記載の亜鉛めっき冷延鋼板。 (3) The galvanized cold-rolled steel sheet according to (1) or (2), wherein the gap has a height from the steel sheet surface of 50 to 1000 nm.
（４）前記酸化物皮膜は、Ｓｉ系酸化物、Ｍｎ系酸化物、及びＳｉとＭｎの複合酸化物から選択される一種以上であることを特徴とする（１）から（３）のいずれか１項に記載の亜鉛めっき冷延鋼板。 (4) The oxide film is one or more selected from Si-based oxides, Mn-based oxides, and complex oxides of Si and Mn. The galvanized cold rolled steel sheet according to item 1.
本発明によれば、鋼の加工性を維持しつつ高強度化に必要な各種合金元素の添加に対して、化成処理の観点での添加制限がなくなる。つまり、延性を下げることなく鋼の高強度化が可能であるため、強度等の確保に必要な材質と化成処理性を両立した亜鉛めっき冷延鋼板が得られる。 According to the present invention, with respect to the addition of various alloy elements necessary for increasing the strength while maintaining the workability of steel, there is no addition limitation from the viewpoint of chemical conversion treatment. That is, since it is possible to increase the strength of the steel without lowering the ductility, a galvanized cold-rolled steel sheet that achieves both the material necessary for securing the strength and the chemical conversion property can be obtained.
以下、本発明の実施形態について説明する。なお、本発明は以下の実施形態に限定されない。 Hereinafter, embodiments of the present invention will be described. In addition, this invention is not limited to the following embodiment.
本発明の亜鉛めっき冷延鋼板は、冷延鋼板の表面に亜鉛電気めっきが形成された亜鉛電気めっき部分と、鋼板表面に酸化物皮膜が形成された酸化物皮膜部分とを備える。 The galvanized cold-rolled steel sheet of the present invention includes a zinc electroplated part in which zinc electroplating is formed on the surface of the cold-rolled steel sheet, and an oxide film part in which an oxide film is formed on the surface of the steel sheet.
冷延鋼板
先ず、冷延鋼板（本明細書において「鋼板」という場合がある）について説明する。冷延鋼板の鋼組成は特に限定されず、Ｆｅ及び不可避不純物以外に、Ｃ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ａｌ、Ｎ等の元素を含有してもよい。
Cold-rolled steel plate First, a cold-rolled steel plate (sometimes referred to as “steel plate” in the present specification) will be described. The steel composition of the cold-rolled steel sheet is not particularly limited, and may contain elements such as C, Si, Mn, P, S, Al, and N in addition to Fe and inevitable impurities.
特に、冷延鋼板がＳｉを含有することで、冷延鋼板の加工性、強度が向上する。この加工性及び強度を向上させる効果を得るためには、Ｓｉを０．５〜３．０質量％の範囲で含有することが好ましい。Ｓｉの含有量が上記範囲にあると、従来、後述するＳｉＯ２等から構成される酸化物皮膜が原因で生じるスケによる化成処理性低下の問題がある。しかし、本発明の技術を使用すると、前述したＳｉの含有量の範囲内において化成処理性の低下がほとんど生じない。 Particularly, when the cold-rolled steel sheet contains Si, workability and strength of the cold-rolled steel sheet are improved. In order to obtain the effect of improving the workability and strength, it is preferable to contain Si in the range of 0.5 to 3.0% by mass. When the content of Si is in the above range, there is a problem of chemical conversion treatment deterioration due to scaling caused by an oxide film composed of SiO 2 or the like described later. However, when the technique of the present invention is used, the chemical conversion treatment performance hardly deteriorates within the above-described Si content range.
また、冷延鋼板がＭｎを含有することで、冷延鋼板の強度が向上する。この強度を向上させる効果を得るためには、Ｍｎを１．０〜３．０質量％の範囲で含有することが好ましい。Ｍｎの含有量が上記範囲にあると、従来、後述するＭｎＯ等から構成される酸化物皮膜が原因で生じるスケによる化成処理性低下の問題がある。しかし、本発明の技術を使用すると、前述したＭｎの含有量の範囲内において化成処理性の低下がほとんど生じない。 Moreover, the intensity | strength of a cold-rolled steel plate improves because a cold-rolled steel plate contains Mn. In order to obtain the effect of improving the strength, it is preferable to contain Mn in the range of 1.0 to 3.0% by mass. When the content of Mn is in the above range, there is a problem of chemical conversion treatment deterioration due to scaling caused by an oxide film composed of MnO or the like which will be described later. However, when the technique of the present invention is used, the chemical conversion treatment performance hardly deteriorates within the range of the Mn content described above.
冷延鋼板の製造方法は特に限定されないが、一般的に冷延鋼板は、水素を含有した非酸化性雰囲気中、９００℃以下の温度で、冷圧された鋼板を熱処理することによって製造される。 Although the manufacturing method of a cold-rolled steel plate is not specifically limited, Generally, a cold-rolled steel plate is manufactured by heat-treating the cold-pressed steel plate at a temperature of 900 ° C. or less in a non-oxidizing atmosphere containing hydrogen. .
酸化物皮膜部分
酸化物皮膜部分の酸化物皮膜は、冷延鋼板製造の際の非酸化性雰囲気中での加熱等により、鋼板の鋼成分のうち易酸化性元素が、鋼板表面に酸化物として濃化する現象により形成される。酸化物皮膜を構成する酸化物として、ＳｉＯ２、ＭｎＯやＳｉ−Ｍｎ系複合酸化物が挙げられる。実際に自動車用鋼板として使用される高強度冷延鋼板については、主として、上記例示するようなＳｉやＭｎの酸化物が鋼板表面に濃化し、かつこれらの表面濃化酸化物は化成処理皮膜形成反応を阻害する。本発明は、これらの酸化物の表面濃化に対して効果を奏するものである。また、本発明によれば、上記以外の種類の酸化物が形成される場合であっても効果を得ることは可能である。
Oxide film part The oxide film part of the oxide film part is easily oxidized in the non-oxidizing atmosphere during the production of cold-rolled steel sheets, and the oxidizable elements are converted into oxides on the steel sheet surface. It is formed by the phenomenon of thickening. As oxide constituting the oxide film, SiO 2, MnO and Si-Mn-based composite oxides. For high-strength cold-rolled steel sheets that are actually used as steel sheets for automobiles, mainly the oxides of Si and Mn as exemplified above are concentrated on the steel sheet surface, and these surface-enriched oxides form a conversion treatment film. Inhibits the reaction. The present invention has an effect on the surface concentration of these oxides. Further, according to the present invention, it is possible to obtain an effect even when oxides other than the above are formed.
酸化物皮膜部分は、鋼板表面に垂直な断面を断面視したときに、鋼板表面と酸化物皮膜との間に隙間を有する。この隙間に後述する金属Ｚｎが存在することで、酸化物皮膜の存在による化成処理性の低下を抑えられる。 The oxide film portion has a gap between the steel sheet surface and the oxide film when a cross section perpendicular to the steel sheet surface is viewed in cross section. By virtue of the presence of metal Zn, which will be described later, in this gap, it is possible to suppress a decrease in chemical conversion property due to the presence of the oxide film.
上記隙間は、鋼板表面からの高さが５０〜１０００ｎｍであることが好ましい。５０ｎｍよりも小さい隙間の場合には、化成処理結晶の生成に必要な量の金属Ｚｎが隙間に析出できない場合があり、また、化成処理時の処理液の侵入も十分でなくなるためである。一方、隙間が大きい場合には、充分な量の金属Ｚｎが隙間に析出されることから、技術的に上限を規定する必要はないと考えられる。ただし、鋼板表面からの高さが、ある値以上になると、もはや隙間としては存在しえず、酸化物が鋼板表面から脱離する場合があるので、本発明において、鋼板表面からの高さの好ましい上限を１０００ｎｍとする。 The gap preferably has a height from the steel plate surface of 50 to 1000 nm. When the gap is smaller than 50 nm, the amount of metal Zn necessary for the formation of the chemical conversion treatment crystal may not be deposited in the gap, and the penetration of the treatment liquid during the chemical conversion treatment may not be sufficient. On the other hand, when the gap is large, a sufficient amount of metal Zn is deposited in the gap, so it is considered unnecessary to define the upper limit technically. However, when the height from the steel sheet surface exceeds a certain value, it can no longer exist as a gap, and the oxide may be detached from the steel sheet surface. A preferable upper limit is set to 1000 nm.
この隙間の大きさの測定方法は特に限定されないが、通常の機械研磨を行った亜鉛めっき冷延鋼板に対して断面観察を行っても、隙間を明瞭に観察できないことが多い。これに対して、例えばＦＩＢ（Ｆｏｃｕｓｅｄ Ｉｏｎ Ｂｅａｍ）により断面加工を行った亜鉛めっき冷延鋼板に対して、ＳＥＭ（Ｓｃａｎｎｉｎｇ Ｅｌｅｃｔｒｏｎ Ｍｉｃｒｏｓｃｏｐｅ）観察を行うと、この隙間の大きさを測定することが容易である。なお、実際の隙間は均一な大きさではないので、ある視野において観察した亜鉛めっき冷延鋼板に対して、その領域で最も大きい隙間の上記高さ（最大値）と、上記領域で最も小さい隙間の上記高さ（最小値）がともに本発明で規定する５０〜１０００ｎｍの範囲内にあれば好ましいとする。なお、ある視野において観察した亜鉛めっき冷延鋼板に対して、その領域で、上記高さが５０ｎｍを下回る隙間、上記高さが１０００ｎｍを上回る隙間が、本発明の効果を害さない範囲で、少量存在してもよい。 The method for measuring the size of the gap is not particularly limited, but even when a cross-sectional observation is performed on a galvanized cold-rolled steel sheet subjected to normal mechanical polishing, the gap cannot often be clearly observed. On the other hand, for example, when SEM (Scanning Electron Microscope) observation is performed on a galvanized cold-rolled steel sheet that has been cross-section processed by FIB (Focused Ion Beam), it is easy to measure the size of the gap. is there. In addition, since the actual gap is not a uniform size, with respect to the galvanized cold-rolled steel sheet observed in a certain field of view, the height (maximum value) of the largest gap in the region and the smallest gap in the region It is preferable that both the above heights (minimum values) are within the range of 50 to 1000 nm defined in the present invention. In addition, with respect to the galvanized cold-rolled steel sheet observed in a certain field of view, in the region, the gap having a height of less than 50 nm and the gap having a height of more than 1000 nm do not impair the effects of the present invention. May be present.
上記の隙間を、鋼板と酸化物皮膜の間に形成する方法としては、例えば、冷延鋼板に対して、硫酸を用いた電解酸洗を行う方法が挙げられる。この方法はＦｅ成分を溶解させるために冷延鋼板側を陽極として電解を実施するものである。電流密度や通電時間を調整すれば、所定の隙間が得られる。具体的には、電流密度を高く、かつ通電時間を長くすれば隙間をより大きくすることができるが、これらの値は実際の設備長さや許容される処理時間とのバランスにより、前述した隙間の大きさとなるように調整すればよい。 Examples of the method for forming the gap between the steel plate and the oxide film include a method of performing electrolytic pickling using sulfuric acid on a cold-rolled steel plate. In this method, electrolysis is performed using the cold-rolled steel sheet side as an anode in order to dissolve the Fe component. By adjusting the current density and the energization time, a predetermined gap can be obtained. Specifically, if the current density is increased and the energization time is lengthened, the gap can be made larger, but these values are based on the balance between the actual equipment length and the allowable processing time, and the gap described above. What is necessary is just to adjust so that it may become a magnitude | size.
酸化物皮膜部分の上記隙間に金属Ｚｎを析出させる方法は特に限定されないが、例えば、下記亜鉛電気めっきの形成の際に、金属Ｚｎを上記隙間に析出させることができる。この場合、亜鉛めっきと金属Ｚｎは同じ成分から構成される。 The method for depositing metal Zn in the gap in the oxide film portion is not particularly limited. For example, the metal Zn can be deposited in the gap during the formation of the following zinc electroplating. In this case, galvanization and metal Zn are comprised from the same component.
亜鉛電気めっき部分
冷延鋼板の表面に形成される亜鉛電気めっきは、電気めっき法により形成されたものをさす。電気めっき法により亜鉛電気めっきを形成する際の条件は特に限定されず適宜設定すればよい。なお、この電気めっきにより、鋼板表面と酸化物皮膜の間の隙間に、金属Ｚｎも析出する。
Zinc electroplating portion Zinc electroplating formed on the surface of a cold-rolled steel sheet refers to one formed by electroplating. Conditions for forming zinc electroplating by electroplating are not particularly limited and may be set as appropriate. The electroplating also deposits metal Zn in the gap between the steel plate surface and the oxide film.
亜鉛電気めっき及び金属Ｚｎによる化成処理性改善効果を得るためには、Ｚｎ量（亜鉛電気めっきと金属Ｚｎの合計量）として１００〜５０００ｍｇ／ｍ２が必要である。これは、酸化物皮膜部分（鋼板と酸化物皮膜に挟まれて金属Ｚｎが存在する部分）を含めて、鋼板全体をＺｎが被覆するために必要な最低のＺｎ量が１００ｍｇ／ｍ２であるためである。Ｚｎ量が１００ｍｇ／ｍ２を下回ると化成皮膜を形成するのに必要なＺｎ源が十分でない。一方、Ｚｎ量が多くなっても化成処理性の観点で問題はないが、冷延鋼板自身の化成処理性改善の目的のみではＺｎ量増加はコストアップにつながるため、上限は５０００ｍｇ／ｍ２とする。 In order to obtain the effect of improving the chemical conversion treatment by zinc electroplating and metal Zn, 100 to 5000 mg / m 2 is necessary as the Zn amount (total amount of zinc electroplating and metal Zn). This is the minimum amount of Zn required to cover the entire steel sheet, including the oxide film part (the part where metal Zn exists between the steel sheet and the oxide film), is 100 mg / m 2 . Because. If the Zn content is less than 100 mg / m 2 , the Zn source necessary for forming the chemical conversion film is not sufficient. On the other hand, even if the amount of Zn increases, there is no problem from the viewpoint of chemical conversion property, but the increase in Zn amount leads to cost increase only for the purpose of improving the chemical conversion property of the cold-rolled steel sheet itself, so the upper limit is 5000 mg / m 2 . To do.
亜鉛電気めっき部分の面積率は、鋼板表面全体に対して、６０％以上であることが好ましい。これは、亜鉛電気めっき部分の面積率が少ない、つまり、酸化物皮膜部分の面積率が多いと、仮に酸化物皮膜と鋼板の間の隙間に金属Ｚｎが析出していたとしても、この酸化物皮膜の部分を完全に覆いきれる化成結晶が形成されない場合があるためである。この原因として明確なことは言えないが、酸化物皮膜と鋼板の間の隙間は決して大きいものではなく（大きいものであれば、酸化物皮膜は鋼板表面から脱離可能であるため）、亜鉛電気めっき部分及び金属Ｚｎだけで全ての化成結晶形成を賄えず、酸化物皮膜の部分を化成結晶が充分に覆うことができない場合があると推測される。この観点で、亜鉛電気めっき部分を比較的多くすべきであり、上記の通り、面積率として６０％以上が好ましい。この面積率は、実施例にも表記するが、鋼板を焼鈍・熱処理する際の時間を制御すればよい。具体的には、熱処理の温度や時間を調整すれば面積率を制御可能である。考え方としては、温度は低く、また時間は短くすればよい。この際、熱処理の温度としては７００〜９００℃が、時間は１〜５分の間で適宜選択される。 The area ratio of the zinc electroplated portion is preferably 60% or more with respect to the entire steel plate surface. This is because when the area ratio of the zinc electroplating portion is small, that is, when the area ratio of the oxide film portion is large, even if metal Zn is deposited in the gap between the oxide film and the steel plate, this oxide This is because a chemical conversion crystal that completely covers the film portion may not be formed. The reason for this is not clear, but the gap between the oxide film and the steel sheet is never large (because the oxide film can be detached from the steel sheet surface if it is large) It is presumed that the formation of all chemical crystals cannot be achieved with only the plated portion and the metal Zn, and the chemical crystals may not sufficiently cover the portion of the oxide film. In this respect, the zinc electroplating portion should be relatively large, and as described above, the area ratio is preferably 60% or more. Although this area ratio is described also in an Example, what is necessary is just to control the time at the time of annealing and heat processing a steel plate. Specifically, the area ratio can be controlled by adjusting the temperature and time of the heat treatment. The idea is that the temperature is low and the time is short. At this time, 700 to 900 ° C. is appropriately selected as the heat treatment temperature, and the time is appropriately selected between 1 to 5 minutes.
なお、亜鉛電気めっき部分の面積率の測定は、以下の手法により間接的に評価することができる。まず、Ｚｎ量を測定し、１００〜５０００ｍｇ／ｍ２の範囲にあることを確認する。この確認方法としては、塩酸などの酸性溶液にて表面のみを溶解した溶液中のＺｎ量をＩＣＰなどで分析する方法、予めＺｎの検量線を作成し蛍光Ｘ線法にてＺｎ量を測定する方法などが挙げられる。次に、亜鉛電気めっき部分のＺｎと、隙間に存在する金属ＺｎのＺｎを分離すればよい。例えばＥＰＭＡ（Ｘ線マイクロアナライザー）などの手法により表面から検出されるＺｎ強度の分布を測定し、Ｚｎが検出されない部分が、隙間に存在する金属ＺｎのＺｎと考えることができる。言い換えると、Ｚｎが検出される部分の面積率が、亜鉛電気めっき部分の面積率と考えられるから、これが６０％以上となることが好ましい。 In addition, the measurement of the area ratio of a zinc electroplating part can be indirectly evaluated with the following methods. First, the amount of Zn is measured, and it is confirmed that it is in the range of 100 to 5000 mg / m 2 . As a confirmation method, a method in which the amount of Zn in a solution obtained by dissolving only the surface in an acidic solution such as hydrochloric acid is analyzed by ICP or the like, a Zn calibration curve is prepared in advance, and the amount of Zn is measured by a fluorescent X-ray method. The method etc. are mentioned. Next, Zn in the zinc electroplating portion and Zn of metal Zn existing in the gap may be separated. For example, the distribution of Zn intensity detected from the surface is measured by a technique such as EPMA (X-ray microanalyzer), and the portion where Zn is not detected can be considered as Zn of metal Zn present in the gap. In other words, since the area ratio of the portion where Zn is detected is considered to be the area ratio of the zinc electroplating portion, it is preferably 60% or more.
化成処理
化成処理は、酸化物皮膜を有する冷延鋼板に対して電解酸洗を施す等して、鋼板表面と酸化物皮膜の間に所望の隙間を形成し、電気めっきを施して亜鉛電気めっきを形成、及び金属Ｚｎを析出させた後に行われる。
Chemical conversion treatment In the chemical conversion treatment, a cold-rolled steel sheet having an oxide film is subjected to electrolytic pickling to form a desired gap between the surface of the steel sheet and the oxide film, and then electroplating to perform zinc electroplating. And after depositing metal Zn.
通常、化成処理は、アルカリ脱脂、表面調整、リン酸塩処理の順番で行われる。最初のアルカリ脱脂では、亜鉛めっき冷延鋼板に塗布された防錆油や、自動車ボディ外板のプレス成形時に頻繁に使用されるプレス洗浄油などの油や汚れを除去する。次の表面調整では、リン酸塩処理で形成される化成処理皮膜（リン酸塩結晶から構成される皮膜）の核形成を促進するために、アルカリ脱脂後の亜鉛めっき冷延鋼板表面を調整する。次のリン酸塩処理では、表面調整された亜鉛めっき冷延鋼板表面にリン酸塩結晶（本明細書において、「化成処理結晶」という場合がある）を形成する。化成処理により形成されるリン酸塩結晶は、通常、フォスフォフィライト（Ｚｎ２Ｆｅ（ＰＯ４）２・４Ｈ２Ｏ）であるが、本発明ではかなりのリン酸塩結晶がホパイト（Ｚｎ３（ＰＯ４）２・４Ｈ２Ｏ）となる。従来、Ｐ比（Ｘ線回折により化成処理後の鋼板を分析し、フォスフォフィライトの強度をＰ、ホパイトの強度をＨとした時のＰ／（Ｐ＋Ｈ）の値）が高いほど塗装後耐食性に優れていることが知られていたが、近年では化成処理薬剤や電着塗料の改善が急速に進んでいるため、塗装後の性能に及ぼすＰ比の影響が問題になることはない。 Usually, the chemical conversion treatment is performed in the order of alkali degreasing, surface conditioning, and phosphate treatment. In the first alkaline degreasing, oil and dirt such as rust preventive oil applied to galvanized cold-rolled steel sheets and press cleaning oil frequently used in press molding of automobile body outer plates are removed. In the next surface adjustment, the surface of the galvanized cold-rolled steel sheet after alkali degreasing is adjusted in order to promote the nucleation of the chemical conversion film (film composed of phosphate crystals) formed by the phosphate treatment. . In the next phosphating treatment, a phosphate crystal (sometimes referred to as “chemical conversion treatment crystal” in this specification) is formed on the surface-adjusted galvanized cold-rolled steel sheet surface. The phosphate crystal formed by the chemical conversion treatment is usually phosphophyllite (Zn 2 Fe (PO 4 ) 2 .4H 2 O). However, in the present invention, a considerable amount of phosphate crystal is formed from hopite (Zn 3 become (PO 4) 2 · 4H 2 O). Conventionally, the higher the P ratio (the value of P / (P + H) when the steel sheet after chemical conversion treatment is analyzed by X-ray diffraction, the strength of phosphophyllite is P and the strength of the hopite is H) is higher, the corrosion resistance after coating However, in recent years, chemical conversion treatment chemicals and electrodeposition coatings have been rapidly improved, so the influence of P ratio on the performance after coating does not become a problem.
上記リン酸塩処理の際、亜鉛電気めっき及び金属Ｚｎが存在しない場合、酸化物皮膜が形成されている部分で、リン酸塩処理に使用される溶液（化成処理液）が鋼板をエッチングし化成結晶を析出する反応が阻害され、化成処理結晶が形成されない部分、いわゆるスケが発生する。亜鉛電気めっき及び金属Ｚｎが存在しないと、このスケが多く発生するため、化成処理性が低い。 When zinc electroplating and metal Zn are not present during the above phosphating, the solution used for phosphating (chemical conversion solution) etches the steel sheet at the part where the oxide film is formed. The reaction for precipitating the crystals is hindered, and a portion where so-called chemical conversion treatment crystals are not formed, so-called skein, is generated. If there is no zinc electroplating and no metallic Zn, a lot of this scale is generated, so that the chemical conversion treatment property is low.
また、上記リン酸塩処理の際、亜鉛電気めっきは冷延鋼板上に形成されているが、隙間の金属Ｚｎが存在しないときに、酸化物皮膜部分が比較的小さい粒状で点在するとみなせる場合には、亜鉛電気めっきのＺｎと化成処理液との接触の際に、Ｚｎが溶解する反応を生じる。その結果、化成処理皮膜の形成に必要な鋼板界面近傍でのｐＨ上昇だけでなく、溶解したＺｎが化成処理皮膜中に取り込まれるため、緻密・かつ均一な化成処理皮膜を形成することができる。一方で、表面濃化した酸化物皮膜部分が膜状に比較的広い面積で存在する場合には、上記効果が認められない。これは、酸化物皮膜が一般的に非導電性物質であるために、これらの上に電気的に金属Ｚｎの皮膜を形成することが不可能であり、この部分では化成処理結晶核の形成に必要なＺｎが不足するためである。また、通常の電気めっき浴は酸性の水溶液であるためＦｅをエッチングする働きは有していると考えられるが、その働きは弱く、表面に膜状に形成された酸化物皮膜を取り除くことができるほどのエッチング力は有していない。いずれにしろ、表面濃化した酸化物皮膜部分が膜状に比較的広い面積で存在する場合、亜鉛電気めっきのみでは、酸化物皮膜による化成皮膜形成阻害は改善されることはない。 In the case of the phosphating, the zinc electroplating is formed on the cold-rolled steel sheet, but when there is no metal Zn in the gap, the oxide film portion can be regarded as being scattered in a relatively small granularity. In the case of contact between zinc electroplating Zn and the chemical conversion solution, a reaction occurs in which Zn dissolves. As a result, not only the pH increase in the vicinity of the steel plate interface necessary for the formation of the chemical conversion coating, but also the dissolved Zn is taken into the chemical conversion coating, so that a dense and uniform chemical conversion coating can be formed. On the other hand, when the oxide film portion having a thickened surface exists in a film with a relatively wide area, the above effect is not recognized. This is because it is impossible to electrically form a metal Zn film on these because the oxide film is generally a non-conductive material. This is because the necessary Zn is insufficient. In addition, it is thought that a normal electroplating bath has an action of etching Fe because it is an acidic aqueous solution, but its action is weak and can remove an oxide film formed in a film shape on the surface. The etching power is not so high. In any case, when the surface-enriched oxide film portion is present in a film with a relatively wide area, the zinc electroplating alone does not improve the conversion film formation inhibition by the oxide film.
しかし、本発明のように、亜鉛電気めっきを形成するとともに、酸化物皮膜部分が隙間を有し、この隙間に金属Ｚｎが存在することで、酸化物皮膜部分が膜状に比較的広い面積で存在する場合であっても化成処理性を改善することができる。酸化物皮膜部分が隙間を有する場合、この隙間の部分では導電可能な鋼板が露出しているため、電気的に金属Ｚｎを析出させることができる。このように、鋼板と酸化物皮膜の隙間に金属Ｚｎが存在すると、化成処理を施した際にも、処理液がこの隙間に侵入し、Ｚｎがエッチングされることで、化成処理結晶の核形成に寄与することができる。また、このＺｎを起点とし、あたかも酸化物皮膜を突き破るように化成結晶が成長するため、化成処理液に対して不活性な酸化物皮膜が存在するような場合においても、緻密かつ均一な化成処理結晶を鋼板表面に形成することができる。 However, as in the present invention, the zinc electroplating is formed, and the oxide film portion has a gap, and the presence of metal Zn in the gap makes the oxide film portion a film with a relatively wide area. Even if it exists, the chemical conversion processability can be improved. In the case where the oxide film portion has a gap, the electrically conductive steel plate is exposed in the gap portion, so that the metal Zn can be electrically deposited. In this way, when metal Zn is present in the gap between the steel sheet and the oxide film, even when chemical conversion treatment is performed, the treatment liquid penetrates into the gap and the Zn is etched, so that nucleation of the chemical conversion crystal is performed. Can contribute. Moreover, since the conversion crystal grows as if it originated from this Zn and breaks through the oxide film, even in the case where an oxide film inert to the chemical conversion solution exists, a dense and uniform chemical conversion treatment is performed. Crystals can be formed on the surface of the steel sheet.
先ず、表1に示した成分組成を有するＡ〜Ｄの鋼を常法の製綱プロセスで溶製し、連続鋳造してスラブとした。次いで、このスラブを１２５０℃に再加熱後、再加熱後のスラブに対して、仕上げ圧延終了温度８５０℃、巻き取り温度６００℃とする熱間圧延を施し、板厚３．０ｍｍの熱延板とした。次いで、この熱延板を、酸洗後、板厚１．５ｍｍまで冷間圧延し供試材とした。この供試材を、ラボの還元加熱シミュレータを使用して水素を１０ｖｏｌ％含有した窒素雰囲気中で８００〜８５０℃の温度範囲で３〜７分保持する加熱処理を実施し焼鈍板（冷延鋼板）を作製した。なお、この際の加熱時間を変化させることで、鋼板表面に形成される膜状の酸化物皮膜の面積率を制御した。 First, steels A to D having the composition shown in Table 1 were melted by a conventional steelmaking process, and continuously cast to obtain a slab. Next, after reheating this slab to 1250 ° C., the reheated slab is hot-rolled to a finish rolling finish temperature of 850 ° C. and a winding temperature of 600 ° C., and a hot-rolled sheet having a thickness of 3.0 mm It was. Subsequently, this hot-rolled sheet was pickled and then cold-rolled to a thickness of 1.5 mm to obtain a test material. This test material was subjected to heat treatment for 3 to 7 minutes in a temperature range of 800 to 850 ° C. in a nitrogen atmosphere containing 10 vol% of hydrogen using a laboratory reduction heating simulator, and then annealed (cold rolled steel sheet) ) Was produced. In addition, the area ratio of the film-like oxide film formed on the steel plate surface was controlled by changing the heating time at this time.
焼鈍板を、１００ｇ／Ｌの硫酸水溶液を使用して、ステンレス板をカソードに用いた電解酸洗に供した。この際、電流密度は１０Ａ／ｄｍ２と一定にし、通電時間を０．５〜５秒の間で変化させた。 The annealed plate was subjected to electrolytic pickling using a stainless steel plate as a cathode using a 100 g / L sulfuric acid aqueous solution. At this time, the current density was kept constant at 10 A / dm 2 , and the energization time was changed between 0.5 and 5 seconds.
酸洗が施された焼鈍板に対して、硫酸亜鉛七水和物１ｍｏｌ／Ｌを含有し、硫酸によりｐＨ２．０に調整した水溶液を用いて、アノードにイリジウムオキサイド板を使用して電気めっきを施し、表面にＺｎを付着させ（表面に亜鉛電気めっきを形成した）、亜鉛電気めっき冷延鋼板とした。Ｚｎの付着量（亜鉛めっきと金属Ｚｎの合計量）は、電流密度と通電時間を変えることで変化させた。付着量は表２に示した。 Electroplating using an iridium oxide plate at the anode using an aqueous solution containing 1 mol / L of zinc sulfate heptahydrate and adjusted to pH 2.0 with sulfuric acid, on the pickled annealed plate Then, Zn was adhered on the surface (zinc electroplating was formed on the surface) to obtain a zinc electroplated cold rolled steel sheet. The adhesion amount of Zn (the total amount of zinc plating and metal Zn) was changed by changing the current density and energization time. The amount of adhesion is shown in Table 2.
なお、Ｚｎの付着量は、蛍光Ｘ線分析により測定し、さらに加速電圧：５ｋＶでＸ線マイクロアナライザー（ＥＰＭＡ）分析に供し、Ｚｎのマッピング分析結果より「亜鉛電気めっき部分」の面積率（Ｚｎ面積率）を測定した。面積率を表２に示した。 The amount of Zn deposited was measured by fluorescent X-ray analysis, and further subjected to X-ray microanalyzer (EPMA) analysis at an acceleration voltage of 5 kV. Area ratio) was measured. The area ratio is shown in Table 2.
さらに、亜鉛電気めっき冷延鋼板の一部をＦＩＢ加工に供し、極低加速ＳＥＭにて観察を行い、酸化物皮膜と鋼板界面間の長さを測定した。この測定では、ある視野における、隙間の大きさが最大の部分と最小の部分を抽出した（表２中の酸化物−鋼板の隙間）。 Furthermore, a part of the zinc electroplated cold-rolled steel sheet was subjected to FIB processing and observed with a very low acceleration SEM, and the length between the oxide film and the steel sheet interface was measured. In this measurement, a portion having the largest gap size and a smallest portion in a certain visual field were extracted (the gap between the oxide and the steel plate in Table 2).
得られた亜鉛電気めっき冷延鋼板は、その後、化成処理性の評価と塗装後耐食性の評価に供した。 The obtained zinc electroplated cold-rolled steel sheet was then subjected to chemical conversion treatment evaluation and post-coating corrosion resistance evaluation.
化成処理性の評価
アルカリ脱脂（日本パーカライジング社製、ファインクリーナーＦＣ−Ｅ２００１）を施した後に、表面調整（日本パーカライジング社製、ＰＬ−ＺＴＨ）に浸漬し、リン酸塩処理（日本パーカライジング社製、パルボンドＰＢ−Ｌ３０８０）を、浴温：４３℃、処理時間：１２０秒の条件で浸漬し化成処理を行った。化成処理後の鋼板表面を、ＳＥＭを用いて倍率３００倍で１０視野観察し、化成結晶が生成していない領域（スケ）の有無と大きさ、および結晶状態の不均一さにより、以下の５段階（化成評点）で評価した。評価結果は表２に示した。
５点：スケは認められず、また結晶も均一である。
４点：わずかに結晶の不均一も認められるがスケは認められない。
３点：微小なスケが認められる。
２点：比較的大きなスケが認められる。
１点：比較的大きなスケが多数認められる。
Evaluation of chemical conversion treatment After degreasing with alkali (Nippon Parkerizing Co., Ltd., Fine Cleaner FC-E2001), it was immersed in surface conditioning (Nippon Parkerizing Co., Ltd., PL-ZTH), and phosphate treatment (Nippon Parkerizing Co., Ltd., Palbond PB-L3080) was immersed and subjected to chemical conversion treatment under conditions of bath temperature: 43 ° C. and treatment time: 120 seconds. The steel sheet surface after the chemical conversion treatment was observed with 10 fields of view at a magnification of 300 using an SEM, and depending on the presence or absence and size of a region where no chemical conversion crystal was formed (skea) and non-uniformity of the crystal state, the following 5 It was evaluated at the stage (chemical conversion score). The evaluation results are shown in Table 2.
5 points: No scale is observed and the crystals are uniform.
4 points: Slight non-uniformity of the crystal is observed, but no skein is observed.
3 points: Small scale is observed.
2 points: A relatively large scale is observed.
1 point: Many relatively large scales are recognized.
（２）塗装後耐食性の評価
前述した化成処理を行った亜鉛電気めっき冷延鋼板に対して、さらに市販のＥＤ塗装（関西ペイント製、ＧＴ−１０）を塗膜厚：２０μmにて実施した。得られた塗装板にＮＴカッターでクロスカットを入れた後、温塩水（５％ＮａＣｌ、５０℃）に１０日間浸漬した。浸漬後のサンプルはポリエステルテープでクロスカット部を覆い剥離作業を行った後に、カットからの片側の最大剥離幅を測定した。表２に試験結果を示した。
(2) Evaluation of corrosion resistance after coating The zinc electroplated cold-rolled steel sheet subjected to the above-described chemical conversion treatment was further subjected to commercially available ED coating (manufactured by Kansai Paint, GT-10) at a coating thickness: 20 μm. The obtained coated plate was cross-cut with an NT cutter and then immersed in warm brine (5% NaCl, 50 ° C.) for 10 days. The sample after the immersion was covered with a polyester tape to cover the cross-cut portion, and after peeling, the maximum peel width on one side from the cut was measured. Table 2 shows the test results.
表２より、いずれの鋼板もＳｉを多く含んでいるものであり、焼鈍を施したのみで化成処理を行った例（比較例１〜４）では、化成処理皮膜にスケが多く見られる判定であり、また塗装鋼板の温塩水浸漬後の剥離幅も大きい値になっている。これに対して、鋼板表面のＺｎ量が本発明で規定した範囲内にあり、かつ鋼板表面でのＺｎ面積率や、断面での酸化物と鋼板の隙間の大きさが本発明で規定した範囲内にある例（本発明例１〜１６）では、化成処理皮膜状態に対してスケなく均一であり、また温塩水浸漬後の剥離幅も小さく安定していることが分かる。一方、Ｚｎを付着させてもその量が十分でない場合（比較例５〜８）は化成処理性改善効果が認められず、塗装鋼板の温塩水試験結果でも改善はほとんど認められない。さらにＺｎ面積率が十分でない場合（本発明例１７〜２０）、また酸化物と鋼板の隙間が、本発明の好ましい範囲内にない場合（本発明例２１〜２４）は、化成改善効果や塗装鋼板の温塩水試験結果に改善は認められるものの十分でなく、前述した本発明例１〜１６よりは劣る結果となっている。 From Table 2, all the steel plates contain a large amount of Si, and in the examples (Comparative Examples 1 to 4) in which the chemical conversion treatment was performed only by annealing, a lot of scale was found in the chemical conversion coating. In addition, the peel width of the coated steel sheet after immersion in warm salt water is also a large value. On the other hand, the Zn amount on the steel sheet surface is within the range defined by the present invention, and the Zn area ratio on the steel sheet surface and the range of the gap between the oxide and the steel sheet in the cross section are defined by the present invention. In the examples (Invention Examples 1 to 16), it can be seen that the film is uniform with respect to the state of the chemical conversion treatment film, and the peel width after immersion in hot salt water is small and stable. On the other hand, when the amount is not sufficient even if Zn is deposited (Comparative Examples 5 to 8), the chemical conversion treatment property improving effect is not recognized, and the improvement is hardly recognized even in the result of the hot salt water test of the coated steel sheet. Further, when the Zn area ratio is not sufficient (Invention Examples 17 to 20), and when the gap between the oxide and the steel sheet is not within the preferred range of the present invention (Invention Examples 21 to 24), the chemical conversion improving effect and coating Although the improvement is recognized in the hot salt water test result of the steel sheet, it is not sufficient, and is inferior to the above-described inventive examples 1 to 16.
本発明により、合金元素を多く含む高張力冷延鋼板においても塗装前の化成処理性が良好であり、かつ塗装後の耐食性も良好になることから、自動車ボディ用途として適用できる。 According to the present invention, even in a high-tensile cold-rolled steel sheet containing a large amount of alloy elements, the chemical conversion property before coating is good and the corrosion resistance after coating is also good, so that it can be applied as an automobile body application.
Claims (4)
鋼板表面に亜鉛電気めっきが形成された亜鉛電気めっき部分と、鋼板表面に酸化物皮膜が形成された酸化物皮膜部分とを備え、
鋼板表面に垂直な断面を断面視したときに、前記酸化物皮膜部分は、前記鋼板表面と前記酸化物皮膜との間に隙間を有し、
前記隙間の少なくとも一部に、金属Ｚｎが存在し、
前記亜鉛電気めっきと前記金属Ｚｎの合計量が１００〜５０００ｍｇ／ｍ２であることを特徴とする亜鉛めっき冷延鋼板。 A galvanized cold-rolled steel sheet having an oxide film,
A zinc electroplating part in which zinc electroplating is formed on the steel sheet surface, and an oxide film part in which an oxide film is formed on the steel sheet surface,
When the cross section perpendicular to the steel sheet surface is viewed in cross section, the oxide film portion has a gap between the steel sheet surface and the oxide film,
Metal Zn is present in at least a part of the gap,
The galvanized cold-rolled steel sheet, wherein the total amount of the zinc electroplating and the metal Zn is 100 to 5000 mg / m 2 .
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| JP2000087257A (en) * | 1998-09-07 | 2000-03-28 | Nkk Corp | Production of cold rolled steel sheet excellent in coating suitability |
| JP2002294487A (en) * | 2001-03-28 | 2002-10-09 | Sumitomo Metal Ind Ltd | Electrolytic zinc-base plated steel-sheet with high strength |
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| JP2000087257A (en) * | 1998-09-07 | 2000-03-28 | Nkk Corp | Production of cold rolled steel sheet excellent in coating suitability |
| JP2002294487A (en) * | 2001-03-28 | 2002-10-09 | Sumitomo Metal Ind Ltd | Electrolytic zinc-base plated steel-sheet with high strength |
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