WO2013099316A1 - Method for producing cold-rolled steel sheet having excellent chemical conversion properties and excellent corrosion resistance after coating - Google Patents

Method for producing cold-rolled steel sheet having excellent chemical conversion properties and excellent corrosion resistance after coating Download PDF

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Publication number
WO2013099316A1
WO2013099316A1 PCT/JP2012/063102 JP2012063102W WO2013099316A1 WO 2013099316 A1 WO2013099316 A1 WO 2013099316A1 JP 2012063102 W JP2012063102 W JP 2012063102W WO 2013099316 A1 WO2013099316 A1 WO 2013099316A1
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Prior art keywords
steel sheet
chemical conversion
cold
rolled steel
coating
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PCT/JP2012/063102
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French (fr)
Japanese (ja)
Inventor
平　章一郎
大塚　真司
吉見　直人
杉本　芳春
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Ｊｆｅスチール株式会社
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Application filed by Ｊｆｅスチール株式会社 filed Critical Ｊｆｅスチール株式会社
Priority to KR1020147019016A priority Critical patent/KR101639926B1/en
Priority to CN201280064512.3A priority patent/CN104024476B/en
Publication of WO2013099316A1 publication Critical patent/WO2013099316A1/en

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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/22—Electroplating: Baths therefor from solutions of zinc
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
    • B32B15/013—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/78—Pretreatment of the material to be coated
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/34—Pretreatment of metallic surfaces to be electroplated
    • C25D5/36—Pretreatment of metallic surfaces to be electroplated of iron or steel
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/48—After-treatment of electroplated surfaces

Definitions

  • the present invention relates to a method for producing a cold-rolled steel sheet which forms a sufficient chemical conversion film and has good corrosion resistance after coating.
  • a method of strengthening a solid solution by adding an alloy element such as Si or Mn, a method of refining crystal grains, and adding a precipitate forming element such as Nb, Ti, or V A method of strengthening and a method of strengthening by generating a hard transformation structure such as a martensite phase are effective.
  • Si is an element effective in increasing the strength while ensuring ductility, because the effect of lowering the ductility is small compared to other elements. For this reason, it may be said that the addition of Si is almost essential for a steel sheet that achieves both workability and high strength.
  • Patent Document 1 discloses a cold-rolled steel sheet on which an oxide having an atomic ratio [Si / Mn] of 1 or less is formed on the surface, and (Si / Mn) ratio of the steel sheet component, annealing temperature as a manufacturing method thereof, The thing which prescribed
  • the annealing temperature needs to be lowered as the amount of Si in the steel sheet component increases, so if high temperature annealing is required to obtain the desired strength and elongation, the moisture ratio of the atmosphere must be increased.
  • Patent Document 2 the size of Si—Mn composite oxide on the surface of the steel sheet and the number per unit area with respect to the steel sheet of Si: 0.05 to 2% and [Si] / [Mn] ⁇ 0.4.
  • a high-strength cold-rolled steel sheet has been proposed that defines a steel sheet surface coverage of an oxide mainly composed of Si.
  • Patent Document 3 describes the (Mn / Si) ratio of the Mn-Si composite oxide on the steel sheet surface to the steel sheet of Si: 0.1 to 1% and [Si] / [Mn] ⁇ 0.4.
  • a high-strength cold-rolled steel sheet that defines the size, the number per unit area, and the steel sheet surface coverage of an oxide mainly composed of Si has been proposed.
  • Patent Document 4 the (Mn / Si) ratio of the Mn—Si composite oxide on the steel sheet surface is compared with the steel sheet of Si: 0.1 to 2% and [Si] / [Mn] ⁇ 0.4.
  • a high-strength cold-rolled steel sheet that defines the size, the number per unit area, and the steel sheet surface coverage of an oxide mainly composed of Si has been proposed.
  • Patent Documents 2 to 4 can be applied to steel sheets containing up to 2% Si, and examples of the production method include pickling conditions after hot rolling and dew point during continuous annealing. It is supposed to be kept below -40 ° C. However, it is necessary for the steel sheet to satisfy a specific Si / Mn ratio, and there is a drawback that the degree of freedom of the steel sheet components is small. Further, setting the dew point during continuous annealing to ⁇ 40 ° C. or less is a technique that is not suitable for mass production because it is considerably difficult to control considering the dew point fluctuation of an actual production line.
  • Patent Document 5 discloses a cold-rolled steel sheet that defines the surface coverage of the Si-based oxide on the steel sheet surface with respect to a steel sheet of Si: 0.4% or more and [Si] / [Mn] ⁇ 0.4. A manufacturing method for pickling after annealing has 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.
  • Patent Document 7 discloses that after annealing a steel sheet containing Si: 0.5 to 2.0%, it was 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 pH of 10 to 14 and a temperature. There has been proposed a technique of performing a treatment for 2 to 50 seconds with an alkaline solution at 10 to 100 ° C.
  • Patent Documents 5 to 7 all remove the oxide layer formed on the surface after annealing, but in the example of Patent Document 5, a high-concentration acid is used to remove the Si-based oxide. In this case, since the formation of a passive film on the iron base is promoted, there is a drawback that it does not necessarily improve the chemical conversion property. In Patent Documents 6 and 7, it is necessary to provide a section for grinding or an acidic solution treatment ⁇ alkali solution treatment section in the line, which leads to an increase in equipment length and cost, which is not realistic.
  • Patent Document 8 discloses a technique for achieving both mold galling resistance and chemical conversion treatment properties by having a Zn plating film with an adhesion amount of 10 to 2000 mg / m 2 on the surface of a steel sheet and having a predetermined crystal orientation.
  • This technology is mainly intended to improve mold galling resistance.
  • microcells are formed between the Zn adhering part and the steel sheet exposed part even with a small amount of Zn adhering. This suggests that the chemical conversion reaction becomes active.
  • Si concentration of the steel plate is high, a considerable portion of the steel plate surface is covered with SiO 2 oxide, and if this portion is a steel plate exposed portion, it cannot be said that microcells are necessarily formed. .
  • a sulfuric acid bath is used as the electroplating bath, and when a Zn plating film is formed under the same conditions presented in the examples, sufficient degreasing cannot be performed depending on the type of alkaline degreasing solution before chemical conversion treatment. I understood that.
  • JP-A-4-276060 Japanese Patent No. 3934604 JP 2005-290440 A Japanese Patent No. 3889768 JP 2004-323969 A JP 2003-226920 A JP 2007-009269 A JP 2006-299351 A
  • An object of the present invention is to provide a method for producing a cold-rolled steel sheet having excellent chemical conversion properties and post-coating corrosion resistance for steel sheets containing Si as a reinforcing element.
  • the inventors of the present invention focused on the fact that when SiO 2 is formed on the surface of the steel sheet, chemical conversion crystal formation reaction does not occur in the formed portion because Fe, which is the main component of the steel sheet, does not dissolve.
  • the present inventors considered that the formation of a dissolution reaction on the surface of a steel sheet by some method leads to a chemical conversion crystal formation reaction.
  • metal Zn forms a zinc phosphate film as a chemical conversion film by reaction with a chemical conversion treatment solution.
  • the Zn layer is not only a zinc layer uniformly attached to one surface of the cold-rolled steel sheet, but also non-uniformly attached to the surface of the cold-rolled steel sheet, and partially forms a layer on the surface of the cold-rolled steel sheet. It also includes a discontinuous zinc layer.
  • the chemical conversion treatment is a general process that proceeds in the order of alkaline degreasing ⁇ surface conditioning ⁇ phosphate treatment.
  • oil is mixed one after another, so in the actual line Degreasing ability is considerably inferior.
  • a steel sheet that has been electroplated with Zn and washed with water is immersed in a degreasing solution that assumes such a real line, the rust preventive oil applied to the steel sheet cannot be removed sufficiently and water repelling occurs.
  • the inventors have found.
  • the steel sheet with such water repellency has poor wettability with the chemical conversion solution as it is and surface unevenness occurs, it is important to completely remove oil on the surface of the steel sheet after alkaline degreasing. From this point of view, after applying electro-Zn plating and washing with water, the oil content of the steel sheet can be removed even when using a degreasing solution assuming an actual line by further contacting with an aqueous solution containing P. It was found that a water wetting rate was obtained.
  • the present invention has been made based on the above findings, and the gist thereof is as follows. [1] After applying electro-Zn plating so that the amount of Zn deposited on the cold-rolled steel sheet is 100 to 5000 mg / m 2 and washing with water, it contains P, and the concentration of P is 0.001 to 2 g / L. A method for producing a cold-rolled steel sheet having excellent chemical conversion treatment properties and post-coating corrosion resistance, wherein the cold-rolled steel sheet is brought into contact with an aqueous solution having a temperature in the range of 30 to 60 ° C.
  • Electroplating Zn so that the adhesion amount of Zn is 100 to 1000 mg / m 2 on the surface of the cold-rolled steel sheet, washing with water, containing P, and the concentration of P being 0.001 to 2 g / L A method for producing a cold-rolled steel sheet having excellent chemical conversion treatment properties and post-coating corrosion resistance, wherein the cold-rolled steel sheet is brought into contact with an aqueous solution having a temperature in the range of 30 to 60 ° C.
  • a cold-rolled steel sheet having excellent chemical conversion properties and post-coating corrosion resistance can be obtained.
  • Adequate chemical conversion film is applied even to steel sheets that are difficult to form in the coating process in automobile manufacturing because of the oxides of Si and Mn, which are known as surface concentrating elements. It can be formed and good post-coating corrosion resistance can be obtained.
  • a cold-rolled steel sheet is produced by subjecting a cold-rolled steel sheet to a heat treatment in a range of 700 to 900 ° C. in a reducing atmosphere containing hydrogen.
  • heating in a reducing atmosphere causes a phenomenon in which easily oxidizable elements of steel plate components are concentrated as oxides on the surface of the steel plate (hereinafter sometimes referred to as surface concentration).
  • surface concentration there are SiO 2, MnO and Si-Mn-based composite oxide.
  • the element that reacts with the chemical conversion treatment liquid is steel sheet component Fe.
  • this Zn becomes an element that reacts with the chemical conversion solution.
  • the phosphoric acid crystal to be formed also forms phosphophyllite (Zn 2 Fe (PO 4 ) 2 .4H 2 O) in a normal cold-rolled steel sheet.
  • a considerable amount of phosphate crystals becomes hopite (Zn 3 (PO 4 ) 2 .4H 2 O).
  • the amount of Zn attached to the steel sheet surface needs to be 100 mg / m 2 or more.
  • Zn applied to the surface functions to form a chemical conversion treatment crystal, and thus the steel plate surface needs to be sufficiently covered. That is, when the adhesion amount is less than 100 mg / m 2 , Zn cannot cover the steel sheet surface, and improvement of the chemical conversion treatment is not recognized.
  • the upper limit is 5000 mg / m 2 . . From the viewpoint of further suppressing an increase in cost, it is preferably 1000 mg / m 2 or less.
  • the electroplating method is the best in the present invention. In this invention, it is because the suitable adhesion amount of Zn which has an effect is 5000 mg / m ⁇ 2 > or less, for example, it cannot respond to such thin plating with a hot dipping method.
  • the usual chemical conversion treatment is performed in the order of alkali degreasing ⁇ surface adjustment ⁇ phosphate treatment.
  • the first alkaline degreasing step it is necessary to remove rust preventive oil applied to the steel sheet, press washing oil frequently used during press molding of the automobile body outer plate, and the like.
  • the oil is not always removed.
  • oil may be mixed in or deterioration of the alkaline degreasing solution may be considered.
  • the surface conditioning liquid is not properly applied, and in the next phosphating process, there is an adverse effect on the phosphating process, such as a part where the phosphate crystals are coarsened or crystals are not formed. There is.
  • the electrode is immersed in a P (phosphorus) -containing aqueous solution after being subjected to electro Zn plating.
  • a P phosphorus
  • electro Zn plating a P (phosphorus) -containing aqueous solution
  • a small amount of P adheres to the surface, which makes it possible to sufficiently degrease even when the deterioration of the alkaline degreasing solution is considered.
  • this mechanism is presumed, when a general zinc sulfate bath is used as the electro-Zn plating bath, sulfate radicals are incorporated into the Zn plating film, and this sulfate radical increases the affinity with oil. It will be difficult.
  • the P concentration of the aqueous solution containing P brought into contact with the steel sheet is preferably in the range of 0.001 to 2 g / L. This is because if it is less than 0.001 g / L, the washing effect of sulfate radicals is small, and the adhesion of P to the surface may not be sufficient. On the other hand, even if it exceeds 2 g / L, there is no significant difference in effect.
  • the temperature of the aqueous solution containing P is preferably in the range of 30 to 60 ° C. This is because if it is less than 30 ° C., it takes time to wash the sulfate radicals and adhere P, and the continuous annealing equipment requires long equipment. On the other hand, if the temperature exceeds 60 ° C., the effect is sufficient, but it is not economically appropriate because an extra facility for heating is required.
  • the method of bringing the steel sheet into contact with the aqueous solution containing P there is no particular limitation on the method of bringing the steel sheet into contact with the aqueous solution containing P.
  • an immersion method or a spray method can be employed.
  • the spray pressure, the nozzle diameter, the distance from the nozzle to the steel plate, and the like when the spray method is adopted only have to satisfy sufficient conditions for the aqueous solution to come into contact with the steel plate, and the conditions are not particularly limited.
  • Si is used for example. It is suitably used for high-strength cold-rolled steel sheets containing 0.5% or more.
  • the amount of Zn adhered to the steel sheet surface is 100-5000 mg / m 2 and Zn is adhered, that is, the presence of a slight amount of Zn on the steel sheet surface is recognized as an improvement in corrosion resistance after coating.
  • this invention is a technique by which chemical conversion property and corrosion resistance after coating are ensured for all cold-rolled steel sheets.
  • Steels A to H having the composition shown in Table 1 are melted by a conventional steelmaking process, continuously cast into a slab, and then the slab is reheated to 1250 ° C., and the finish rolling finish temperature is set.
  • Hot rolling was performed at 850 ° C. and a coiling temperature of 600 ° C. to obtain a hot rolled sheet having a thickness of 3.0 mm.
  • the hot-rolled sheet was pickled and then cold-rolled to a plate thickness of 1.5 mm to obtain a test material.
  • This test material was heat-treated in a nitrogen atmosphere containing 10 vol% of hydrogen in a range of 800 to 850 ° C. for 2 minutes at maximum using a laboratory reduction heating simulator to prepare an annealed plate (cold rolled steel plate).
  • an iridium oxide plate is used for the anode using an aqueous solution containing zinc sulfate heptahydrate: 1 mol / L and adjusted to pH 2.0 using sulfuric acid.
  • the amount of Zn deposited was varied by changing the current density and the energization time.
  • an annealed plate (cold rolled steel plate) that was not electroplated and did not adhere Zn to the surface was also prepared.
  • the cold-rolled steel sheet degreased with the degreasing liquid diluted to twice the specified concentration described above is immersed in a surface conditioning liquid (manufactured by Nihon Parkerizing Co., Ltd., PL-ZTH), and a phosphate treatment liquid (Nippon Parkerizing).
  • Chemical conversion treatment was performed by dipping in Palbond PB-L3080 manufactured by Co., Ltd. under conditions of bath temperature: 43 ° C. and treatment time: 120 seconds.
  • the surface of the cold-rolled steel sheet after the chemical conversion treatment is observed with a SEM at 10 magnifications at a magnification of 300 times. Evaluation was made according to the following five grades. 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.
  • the steel plate after the chemical conversion treatment was further applied with a commercially available ED coating (manufactured by Kansai Paint Co., Ltd., GT-10) at a coating thickness: 20 ⁇ m, and a cross cut was put on the coated surface with an NT cutter (registered trademark). Then, it was immersed in warm salt water (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. The results obtained as described above are shown in Tables 2 to 5 together with the conditions.
  • steels A, B, and C do not contain much Si in the steel plate components, so that good chemical conversion treatment is possible even in the examples where the surface is not subjected to electro-Zn plating (Comparative Examples 1 to 3). Although obtained, the peel width is large and the corrosion resistance after coating is poor.
  • steels D to H contain a large amount of Si, in the examples (Comparative Examples 4 to 8) in which the surface is not plated with Zn, scaling is observed in the chemical crystals, and in particular, the Si amount is 1.5% or more. In G and H, it became the level of the grade 1 in which almost no chemical conversion crystal was formed.

Abstract

Electrolytic Zn plating is carried out on the surface of a cold-rolled steel sheet so that the adhesion amount of Zn is 100-5,000 mg/m2, and the resulting cold-rolled steel sheet is washed with water and then brought into contact with an aqueous solution containing P. In this connection, the P concentration of the aqueous solution containing P is 0.001-2 g/L and the temperature of the aqueous solution containing P is within the range of 30-60˚C.

Description

化成処理性および塗装後耐食性に優れた冷延鋼板の製造方法Method for producing cold-rolled steel sheet with excellent chemical conversion and post-coating corrosion resistance
　本発明は、十分な化成皮膜を形成し、かつ塗装後耐食性が良好な冷延鋼板の製造方法に関するものである。 The present invention relates to a method for producing a cold-rolled steel sheet which forms a sufficient chemical conversion film and has good corrosion resistance after coating.
　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、今度は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、板厚を薄くするとともに、板厚を薄くすることによって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動きが徐々に高まり、至近では引張強度１１８０ＭＰａクラスの高強度鋼板においても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. To reduce the weight of the car body, it is most effective to reduce the thickness of the steel sheet used.However, if the steel sheet strength is kept the same while the steel sheet strength remains the same, the rigidity of the steel sheet decreases, and this time the passenger is in a collision. It becomes impossible to secure safety. For this reason, the movement of adopting high strength steel plate as a body material is gradually increased, and the tensile strength is 1180 MPa in the near future. Even in the class of high-strength steel sheets, the movement to use for body use has become active.
　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する方法、結晶粒を微細化する方法、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 a steel sheet, a method of strengthening a solid solution by adding an alloy element such as Si or Mn, a method of refining crystal grains, and adding a precipitate forming element such as Nb, Ti, or V A method of strengthening and a method of strengthening by generating a hard transformation structure such as a martensite phase are effective.
　一般に、合金元素の添加による高強度化は、一方で延性の低下を招くため、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、固溶強化の中でも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の添加がほぼ必須と言ってよい。 Generally, increasing the strength by adding an alloying element, on the other hand, causes a decrease in ductility, so that there is a drawback that it is difficult to perform press molding to form the shape of a part. However, among solid solution strengthening, Si is an element effective in increasing the strength while ensuring ductility, because the effect of lowering the ductility is small compared to other elements. For this reason, it may be said that the addition of Si is almost essential for a steel sheet that achieves both workability and high strength.
　しかしながら、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容易に酸化されることから、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、ＳｉＯ２が化成処理液と鋼板の反応を阻害するため、化成結晶が形成されない所謂スケと呼ばれる部分が存在することになる。このような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り、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。そのためＳｉを含有する高強度冷延鋼板をボディ用途に使用することは非常に困難であった。 However, since the equilibrium oxygen partial pressure of oxide is very low and Si is easily oxidized in a reducing atmosphere in a continuous annealing furnace used in the production of a general cold-rolled steel sheet, a steel sheet containing Si is used. When passing through the continuous annealing furnace, Si is selectively oxidized on the surface of the steel sheet to form SiO 2 . When the steel sheet 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 sheet, so there is a so-called skein portion where no chemical conversion crystals are formed. It will be. Steel sheets with scale after such chemical conversion treatment may already have rust in the water washing stage after chemical conversion treatment, and even if it does not reach rust, the corrosion resistance of the steel sheet after electrodeposition coating is very high It ’s bad. Therefore, it has been very difficult to use a high-strength cold-rolled steel sheet containing Si for body use.
　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ため、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なければならない。しかし、逆に鋼板表面には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、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技術である。 There have been many proposals for improving the chemical conversion properties of such high-strength cold-rolled steel sheets containing Si. For example, Patent Document 1 discloses a cold-rolled steel sheet on which an oxide having an atomic ratio [Si / Mn] of 1 or less is formed on the surface, and (Si / Mn) ratio of the steel sheet component, annealing temperature as a manufacturing method thereof, 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, the annealing temperature needs to be lowered as the amount of Si in the steel sheet component increases, so if high temperature annealing is required to obtain the desired strength and elongation, the moisture ratio of the atmosphere must be increased. I must. However, since a Fe-based oxide is formed on the surface of the steel plate, it is not established as a product. That is, this is a technique that cannot be applied to steel sheets containing about 1.0% Si, which is the mainstream of current high-strength steel sheets.
　特許文献２には、Ｓｉ：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。 In Patent Document 2, the size of Si—Mn composite oxide on the surface of the steel sheet and the number per unit area with respect to the steel sheet of Si: 0.05 to 2% and [Si] / [Mn] ≦ 0.4. In addition, a high-strength cold-rolled steel sheet has been proposed that defines a steel sheet surface coverage of an oxide mainly composed of Si.
　特許文献３には、Ｓｉ：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。 Patent Document 3 describes the (Mn / Si) ratio of the Mn-Si composite oxide on the steel sheet surface to the steel sheet of Si: 0.1 to 1% and [Si] / [Mn] ≦ 0.4. A high-strength cold-rolled steel sheet that defines the size, the number per unit area, and the steel sheet surface coverage of an oxide mainly composed of Si has been proposed.
　特許文献４には、Ｓｉ：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。 In Patent Document 4, the (Mn / Si) ratio of the Mn—Si composite oxide on the steel sheet surface is compared with the steel sheet of Si: 0.1 to 2% and [Si] / [Mn] ≦ 0.4. A high-strength cold-rolled steel sheet that defines the size, the number per unit area, and the steel sheet surface coverage of an oxide mainly composed of Si has been proposed.
　特許文献２~４の技術は、最大２％のＳｉを含有する鋼板に対してまで適用可能であり、その製造方法の例としては、熱間圧延後の酸洗条件や連続焼鈍時の露点を−４０℃以下に抑えるとしている。しかし、特定の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ため、量産には適さない技術である。 The techniques of Patent Documents 2 to 4 can be applied to steel sheets containing up to 2% Si, and examples of the production method include pickling conditions after hot rolling and dew point during continuous annealing. It is supposed to be kept below -40 ° C. However, it is necessary for the steel sheet to satisfy a specific Si / Mn ratio, and there is a drawback that the degree of freedom of the steel sheet components is small. Further, setting the dew point during continuous annealing to −40 ° C. or less is a technique that is not suitable for mass production because it is considerably difficult to control considering the dew point fluctuation of an actual production line.
　特許文献５には、Ｓｉ：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。 Patent Document 5 discloses a cold-rolled steel sheet that defines the surface coverage of the Si-based oxide on the steel sheet surface with respect to a steel sheet of Si: 0.4% or more and [Si] / [Mn] ≧ 0.4. A manufacturing method for pickling after annealing has been proposed.
　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。 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.
　特許文献７には、Ｓｉ：０．５~２．０％含有する鋼板を焼鈍した後に、ｐＨ０~４、温度１０~１００℃の酸性溶液で５~１５０秒間処理し、かつｐＨ１０~１４、温度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。 Patent Document 7 discloses that after annealing a steel sheet containing Si: 0.5 to 2.0%, it was 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 pH of 10 to 14 and a temperature. There has been proposed a technique of performing a treatment for 2 to 50 seconds with an alkaline solution at 10 to 100 ° C.
　特許文献５~７の技術は、いずれも焼鈍後の表面に形成された酸化物層を除去するものであるが、特許文献５の例では、Ｓｉ基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。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→アルカリ溶液処理の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。 The techniques of Patent Documents 5 to 7 all remove the oxide layer formed on the surface after annealing, but in the example of Patent Document 5, a high-concentration acid is used to remove the Si-based oxide. In this case, since the formation of a passive film on the iron base is promoted, there is a drawback that it does not necessarily improve the chemical conversion property. In Patent Documents 6 and 7, it is necessary to provide a section for grinding or an acidic solution treatment → alkali solution treatment section in the line, which leads to an increase in equipment length and cost, which is not realistic.
　特許文献８には、鋼板表面に付着量が１０~２０００ｍｇ／ｍ２のＺｎ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Ｚｎ付着量においてもＺｎ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、鋼板表面のかなりの部分が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。また、電気めっき浴には、硫酸浴を使用しており、実施例に提示されている同じ条件でＺｎめっき皮膜を形成したところ、化成処理前のアルカリ脱脂液の種類によっては十分な脱脂ができないことが分かった。 Patent Document 8 discloses a technique for achieving both mold galling resistance and chemical conversion treatment properties by having a Zn plating film with an adhesion amount of 10 to 2000 mg / m 2 on the surface of a steel sheet and having a predetermined crystal orientation. Has been proposed. This technology is mainly intended to improve mold galling resistance. With regard to the chemical conversion processability, microcells are formed between the Zn adhering part and the steel sheet exposed part even with a small amount of Zn adhering. This suggests that the chemical conversion reaction becomes active. However, when the Si concentration of the steel plate is high, a considerable portion of the steel plate surface is covered with SiO 2 oxide, and if this portion is a steel plate exposed portion, it cannot be said that microcells are necessarily formed. . In addition, a sulfuric acid bath is used as the electroplating bath, and when a Zn plating film is formed under the same conditions presented in the examples, sufficient degreasing cannot be performed depending on the type of alkaline degreasing solution before chemical conversion treatment. I understood that.
特開平４−２７６０６０号公報JP-A-4-276060 特許第３９３４６０４号公報Japanese Patent No. 3934604 特開２００５−２９０４４０号公報JP 2005-290440 A 特許第３８８９７６８号公報Japanese Patent No. 3889768 特開２００４−３２３９６９号公報JP 2004-323969 A 特開２００３−２２６９２０号公報JP 2003-226920 A 特開２００７−００９２６９号公報JP 2007-009269 A 特開２００６−２９９３５１号公報JP 2006-299351 A
　このように、延性を低下させずに高強度を図る目的でＳｉを添加した冷延鋼板の場合、化成処理性を満足する技術は未だ十分とは言えず、高強度鋼板の自動車車体への適用を阻害しているのが現状である。 Thus, in the case of cold-rolled steel sheet with Si added for the purpose of increasing strength without reducing ductility, it cannot be said that the technology that satisfies chemical conversion treatment is sufficient, and application of high-strength steel sheet to automobile bodies It is the present condition that is hindering.
　本発明は、Ｓｉを強化元素として含有する鋼板に対して、化成処理性および塗装後耐食性に優れた冷延鋼板の製造方法を提供することを目的とする。 An object of the present invention is to provide a method for producing a cold-rolled steel sheet having excellent chemical conversion properties and post-coating corrosion resistance for steel sheets containing Si as a reinforcing element.
　本発明者らは、ＳｉＯ２が鋼板表面に形成されると、形成された部分では、鋼板の主成分であるＦｅが溶解しないため、化成結晶形成反応が生じないことに着目した。また、本発明者らは、なんらかの方法で鋼板表面の溶解反応を生じさせることが化成結晶形成反応に結びつくと考えた。また、本発明者らは、金属Ｚｎは化成処理液との反応により、化成皮膜としてリン酸亜鉛皮膜を形成することを考えた。検討の結果、リン酸亜鉛皮膜を形成するのに十分なだけの量の薄いＺｎ層を冷延鋼板表面に付与することで、Ｓｉを含有する冷延鋼板に対しても化成結晶形成反応が進行し、その結果、化成処理後にリン酸亜鉛被膜を形成できることを、本発明者らは確認した。なお、上記のＺｎ層とは、冷延鋼板表面の一面に均一に付着した亜鉛層のみならず、冷延鋼板表面に不均一に付着していて、冷延鋼板表面に部分的に層をなし、不連続な亜鉛層をも含むものとする。 The inventors of the present invention focused on the fact that when SiO 2 is formed on the surface of the steel sheet, chemical conversion crystal formation reaction does not occur in the formed portion because Fe, which is the main component of the steel sheet, does not dissolve. In addition, the present inventors considered that the formation of a dissolution reaction on the surface of a steel sheet by some method leads to a chemical conversion crystal formation reaction. The present inventors also considered that metal Zn forms a zinc phosphate film as a chemical conversion film by reaction with a chemical conversion treatment solution. As a result of the study, by applying a thin Zn layer sufficient to form a zinc phosphate coating on the surface of the cold-rolled steel sheet, the reaction for forming a chemical crystal proceeds on the cold-rolled steel sheet containing Si. As a result, the present inventors confirmed that a zinc phosphate coating can be formed after the chemical conversion treatment. The Zn layer is not only a zinc layer uniformly attached to one surface of the cold-rolled steel sheet, but also non-uniformly attached to the surface of the cold-rolled steel sheet, and partially forms a layer on the surface of the cold-rolled steel sheet. It also includes a discontinuous zinc layer.
　しかしながら、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進行するのが一般的なプロセスであり、このうちアルカリ脱脂工程においては油が次々と混入していくため、実ラインではかなり脱脂能力が劣ってしまう。このような実ラインを想定した脱脂液に、電気Ｚｎめっきを施し水洗しただけの鋼板を浸漬すると、鋼板に付与されている防錆油などが十分に除去できず水はじきが生じることを、本発明者らは見出した。このような水はじきが生じた鋼板は、そのまま化成処理液との濡れ性も悪く表面ムラを生じるため、アルカリ脱脂後には鋼板表面の油分を完全に除去することが重要である。この観点から、電気Ｚｎめっきを施し水洗した後に、さらにＰを含有する水溶液に接触させることで、実ラインを想定した脱脂液を用いた場合でも、鋼板の油分を除去することができ、十分な水濡れ率が得られることがわかった。 However, the chemical conversion treatment is a general process that proceeds in the order of alkaline degreasing → surface conditioning → phosphate treatment. Among these, in the alkaline degreasing step, oil is mixed one after another, so in the actual line Degreasing ability is considerably inferior. When a steel sheet that has been electroplated with Zn and washed with water is immersed in a degreasing solution that assumes such a real line, the rust preventive oil applied to the steel sheet cannot be removed sufficiently and water repelling occurs. The inventors have found. Since the steel sheet with such water repellency has poor wettability with the chemical conversion solution as it is and surface unevenness occurs, it is important to completely remove oil on the surface of the steel sheet after alkaline degreasing. From this point of view, after applying electro-Zn plating and washing with water, the oil content of the steel sheet can be removed even when using a degreasing solution assuming an actual line by further contacting with an aqueous solution containing P. It was found that a water wetting rate was obtained.
　本発明は、以上の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。
［１］冷延鋼板表面にＺｎの付着量が１００~５０００ｍｇ／ｍ２となるように電気Ｚｎめっきを施し、水洗した後に、Ｐを含有し、前記Ｐの濃度が０．００１~２ｇ／Ｌであり、温度が３０~６０℃の範囲である水溶液に前記冷延鋼板を接触させることを特徴とする化成処理性および塗装後耐食性に優れた冷延鋼板の製造方法。
［２］冷延鋼板表面にＺｎの付着量が１００~１０００ｍｇ／ｍ２となるように電気Ｚｎめっきを施し、水洗した後に、Ｐを含有し、前記Ｐの濃度が０．００１~２ｇ／Ｌであり、温度が３０~６０℃の範囲である水溶液に前記冷延鋼板を接触させることを特徴とする化成処理性および塗装後耐食性に優れた冷延鋼板の製造方法。 The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] After applying electro-Zn plating so that the amount of Zn deposited on the cold-rolled steel sheet is 100 to 5000 mg / m 2 and washing with water, it contains P, and the concentration of P is 0.001 to 2 g / L. A method for producing a cold-rolled steel sheet having excellent chemical conversion treatment properties and post-coating corrosion resistance, wherein the cold-rolled steel sheet is brought into contact with an aqueous solution having a temperature in the range of 30 to 60 ° C.
[2] Electroplating Zn so that the adhesion amount of Zn is 100 to 1000 mg / m 2 on the surface of the cold-rolled steel sheet, washing with water, containing P, and the concentration of P being 0.001 to 2 g / L A method for producing a cold-rolled steel sheet having excellent chemical conversion treatment properties and post-coating corrosion resistance, wherein the cold-rolled steel sheet is brought into contact with an aqueous solution having a temperature in the range of 30 to 60 ° C.
　本発明によれば、化成処理性および塗装後耐食性に優れた冷延鋼板が得られる。表面濃化元素として知られるＳｉやＭｎの酸化物が表面に形成されているがゆえに自動車製造での塗装工程において化成処理皮膜が形成されにくくなっている鋼板に対しても、十分な化成皮膜を形成し、かつ良好な塗装後耐食性を得ることができる。 According to the present invention, a cold-rolled steel sheet having excellent chemical conversion properties and post-coating corrosion resistance can be obtained. Adequate chemical conversion film is applied even to steel sheets that are difficult to form in the coating process in automobile manufacturing because of the oxides of Si and Mn, which are known as surface concentrating elements. It can be formed and good post-coating corrosion resistance can be obtained.
　一般に、冷延鋼板は、冷間圧延された鋼板を水素を含有した還元性雰囲気中で７００~９００℃の範囲で熱処理を施すことによって製造される。しかし、還元性雰囲気中で加熱することにより、鋼板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（以下、表面濃化と称することがある）が生じてしまう。この代表的な酸化物としては、ＳｉＯ２、ＭｎＯやＳｉ−Ｍｎ系複合酸化物がある。これらの酸化物が鋼板表面に存在する部分では、化成処理液により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、鋼板表面では部分的に化成結晶が形成されない部分、いわゆるスケが発生し、化成処理性に劣ることになる。 Generally, a cold-rolled steel sheet is produced by subjecting a cold-rolled steel sheet to a heat treatment in a range of 700 to 900 ° C. in a reducing atmosphere containing hydrogen. However, heating in a reducing atmosphere causes a phenomenon in which easily oxidizable elements of steel plate components are concentrated as oxides on the surface of the steel plate (hereinafter sometimes referred to as surface concentration). As the typical oxide, there are SiO 2, MnO and Si-Mn-based composite oxide. In the portion where these oxides are present on the steel sheet surface, the reaction of etching the steel sheet with the chemical conversion solution to precipitate the chemical crystals is hindered, and the part where the chemical crystals are not partially formed on the steel sheet surface, so-called skeins are generated, It will be inferior to chemical conversion processability.
　これに対して、鋼板表面にＺｎめっきを施すと、Ｚｎが表面濃化した酸化物を覆うため、酸化物が存在していた鋼板表面においても、Ｚｎと化成処理液との反応が生じる。また、表面濃化した酸化物を全部覆い尽くすことができなかったとしても、周辺に存在するＺｎが化成処理液と反応するため、化成皮膜を容易に形成することができる。 On the other hand, when Zn plating is performed on the steel sheet surface, Zn is covered with an oxide whose surface has been concentrated, and therefore, the reaction between Zn and the chemical conversion solution occurs even on the steel sheet surface where the oxide was present. Further, even if it is not possible to completely cover the surface-enriched oxide, Zn present in the periphery reacts with the chemical conversion treatment solution, so that a chemical conversion film can be easily formed.
　ここで、通常の冷延鋼板の場合、化成処理液と反応する元素は鋼板成分のＦｅである。しかし、表面にＺｎめっきを施した場合にはこのＺｎが化成処理液と反応する元素になる。また、形成されるリン酸塩結晶も、通常の冷延鋼板ではフォスフォフィライト（Ｚｎ２Ｆｅ（ＰＯ４）２・４Ｈ２Ｏ）が形成される。しかし、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。 Here, in the case of a normal cold-rolled steel sheet, the element that reacts with the chemical conversion treatment liquid is steel sheet component Fe. However, when the surface is plated with Zn, this Zn becomes an element that reacts with the chemical conversion solution. Moreover, the phosphoric acid crystal to be formed also forms phosphophyllite (Zn 2 Fe (PO 4 ) 2 .4H 2 O) in a normal cold-rolled steel sheet. However, in the present invention, a considerable amount of phosphate crystals becomes hopite (Zn 3 (PO 4 ) 2 .4H 2 O).
　このような化成処理性改善の効果を得るためには、鋼板表面へのＺｎの付着量が１００ｍｇ／ｍ２以上である必要がある。先述したように、本技術は表面に付与したＺｎが化成処理結晶を形成する働きをするため、鋼板表面を十分に覆っておく必要がある。すなわち、１００ｍｇ／ｍ２未満の付着量では鋼板表面をＺｎが覆いつくすことができず化成処理の改善が認められない。一方、Ｚｎ付着量が多くなっても化成性の観点では問題ないが、冷延鋼板自身の化成性改善の目的のみではＺｎ付着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。コストアップをさらに抑制する観点からは、好ましくは、１０００ｍｇ／ｍ２以下である。 In order to obtain the effect of improving the chemical conversion property, the amount of Zn attached to the steel sheet surface needs to be 100 mg / m 2 or more. As described above, in the present technology, Zn applied to the surface functions to form a chemical conversion treatment crystal, and thus the steel plate surface needs to be sufficiently covered. That is, when the adhesion amount is less than 100 mg / m 2 , Zn cannot cover the steel sheet surface, and improvement of the chemical conversion treatment is not recognized. On the other hand, even if the Zn deposition amount increases, there is no problem from the viewpoint of chemical conversion, but an increase in the Zn deposition amount leads to an increase in cost only for the purpose of improving the chemical conversion properties of the cold-rolled steel sheet itself, so the upper limit is 5000 mg / m 2 . . From the viewpoint of further suppressing an increase in cost, it is preferably 1000 mg / m 2 or less.
　鋼板表面にＺｎを付着させる方法は種々考えられる。しかし、本発明では電気めっきによる方法が最もよい。本発明において、効果を奏するＺｎの適切な付着量が５０００ｍｇ／ｍ２以下であり、例えば、溶融めっき法ではこのような薄めっきに対応できないためである。 Various methods for attaching Zn to the surface of the steel sheet are conceivable. However, the electroplating method is the best in the present invention. In this invention, it is because the suitable adhesion amount of Zn which has an effect is 5000 mg / m < 2 > or less, for example, it cannot respond to such thin plating with a hot dipping method.
　通常の化成処理は、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工程では、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を除去する必要がある。しかしながら、薄い電気Ｚｎめっきを施した鋼板をそのままアルカリ脱脂液に浸漬させても、必ずしも油を除去できるとは限らない。特に、自動車メーカーの塗装ラインなどで次々と流れてくる何台もの車体に対してアルカリ脱脂をする場合、油が混入したりアルカリ脱脂液の劣化などが考えられる。そのため、場合によっては十分に脱脂が施されず水はじきが生じた状態で次の表面調整工程にまわされる場合がある。このような水はじき部分では、表面調整液がきちんと付与されず、さらに次のリン酸塩処理工程では、リン酸塩結晶が粗大化したり結晶が形成されない部分が存在するなどリン酸塩処理へ悪影響がある。 The usual chemical conversion treatment is performed in the order of alkali degreasing → surface adjustment → phosphate treatment. In the first alkaline degreasing step, it is necessary to remove rust preventive oil applied to the steel sheet, press washing oil frequently used during press molding of the automobile body outer plate, and the like. However, even if a steel plate subjected to thin electric Zn plating is immersed in an alkaline degreasing solution as it is, the oil is not always removed. In particular, when alkali degreasing is performed on a number of vehicle bodies that are flowing one after another in a paint line of an automobile manufacturer, oil may be mixed in or deterioration of the alkaline degreasing solution may be considered. Therefore, depending on the case, it may be sent to the next surface adjustment process in a state where water is not sufficiently degreased and water is repelled. In such a water-repellent part, the surface conditioning liquid is not properly applied, and in the next phosphating process, there is an adverse effect on the phosphating process, such as a part where the phosphate crystals are coarsened or crystals are not formed. There is.
　そこで、本発明では、電気Ｚｎめっきを施した後にＰ（燐）含有水溶液に浸漬することとする。Ｐ含有水溶液に浸漬することで、表面に微量なＰが付着し、これによりアルカリ脱脂液の劣化などを考えた場合でも十分に脱脂が可能となる。このメカニズムについては推定ではあるが、電気Ｚｎめっき浴として一般的な硫酸亜鉛浴を使用すると硫酸根がＺｎめっき皮膜中に取り込まれ、この硫酸根が油との親和性を高めるために、脱脂が困難になると考えられる。これに対して、Ｐを含有する水溶液を鋼板に接触させると、表面に存在する硫酸根が洗い流され、さらにＰが微量に付着することで油との親和性を低くする。そのため、脱脂性が向上すると考えられる。 Therefore, in the present invention, the electrode is immersed in a P (phosphorus) -containing aqueous solution after being subjected to electro Zn plating. By dipping in the P-containing aqueous solution, a small amount of P adheres to the surface, which makes it possible to sufficiently degrease even when the deterioration of the alkaline degreasing solution is considered. Although this mechanism is presumed, when a general zinc sulfate bath is used as the electro-Zn plating bath, sulfate radicals are incorporated into the Zn plating film, and this sulfate radical increases the affinity with oil. It will be difficult. On the other hand, when an aqueous solution containing P is brought into contact with the steel sheet, sulfate radicals existing on the surface are washed away, and further, P adheres in a small amount, thereby lowering the affinity with oil. Therefore, it is considered that the degreasing property is improved.
　鋼板に接触させるＰを含有する水溶液のＰ濃度は、０．００１~２ｇ／Ｌの範囲が好ましい。これは、０．００１ｇ／Ｌ未満であると、硫酸根の洗浄効果が小さく、かつＰの表面への付着が十分でない場合があるためである。一方、２ｇ／Ｌを超えても効果に大きな差は認められないためである。 The P concentration of the aqueous solution containing P brought into contact with the steel sheet is preferably in the range of 0.001 to 2 g / L. This is because if it is less than 0.001 g / L, the washing effect of sulfate radicals is small, and the adhesion of P to the surface may not be sufficient. On the other hand, even if it exceeds 2 g / L, there is no significant difference in effect.
　Ｐを含有する水溶液の温度は、３０~６０℃の範囲が好ましい。３０℃未満であると、硫酸根の洗浄およびＰの付着に時間を要し、連続焼鈍設備では長大な設備を必要とするためである。一方、６０℃を超えると効果は十分であるが、加熱するための設備が余計に必要になるなど経済上適切でないためである。 The temperature of the aqueous solution containing P is preferably in the range of 30 to 60 ° C. This is because if it is less than 30 ° C., it takes time to wash the sulfate radicals and adhere P, and the continuous annealing equipment requires long equipment. On the other hand, if the temperature exceeds 60 ° C., the effect is sufficient, but it is not economically appropriate because an extra facility for heating is required.
　Ｐを含有する水溶液に鋼板を接触させる方法については特に限定はしない。例えば、浸漬方式やスプレー方式など採用することができる。スプレー方式を採用した場合のスプレー圧やノズル径、ノズルから鋼板の距離などは、水溶液が鋼板に接触するだけの十分な条件が満たされていればよく、この条件についても特に限定はしない。 There is no particular limitation on the method of bringing the steel sheet into contact with the aqueous solution containing P. For example, an immersion method or a spray method can be employed. The spray pressure, the nozzle diameter, the distance from the nozzle to the steel plate, and the like when the spray method is adopted only have to satisfy sufficient conditions for the aqueous solution to come into contact with the steel plate, and the conditions are not particularly limited.
　なお、本発明では、焼鈍後の冷延鋼板表面にＳｉＯ２などが存在することで化成皮膜が形成されない鋼板に対して、皮膜の形成を促すことが目的の一つであるため、Ｓｉを例えば０．５％以上含んでいる高強度冷延鋼板などに対して好適に用いられる。しかし、鋼板表面にＺｎの付着量が１００~５０００ｍｇ／ｍ２とＺｎを付着させる、すなわち、鋼板表面へのわずかなＺｎの存在により塗装後耐食性の向上が認められるため、一般的な冷延鋼板に対しても塗装後耐食性の観点から適用が可能である。このため、本発明は、全ての冷延鋼板を対象に化成処理性と塗装後耐食性が確保される技術である。 In the present invention, since one of the purposes is to promote the formation of a film on a steel sheet on which a chemical conversion film is not formed due to the presence of SiO 2 or the like on the surface of the cold-rolled steel sheet after annealing, Si is used for example. It is suitably used for high-strength cold-rolled steel sheets containing 0.5% or more. However, the amount of Zn adhered to the steel sheet surface is 100-5000 mg / m 2 and Zn is adhered, that is, the presence of a slight amount of Zn on the steel sheet surface is recognized as an improvement in corrosion resistance after coating. Can also be applied from the viewpoint of corrosion resistance after painting. For this reason, this invention is a technique by which chemical conversion property and corrosion resistance after coating are ensured for all cold-rolled steel sheets.
　表１に示した成分組成を有するＡ~Ｈ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、次いで、このスラブを１２５０℃に再加熱後、仕上げ圧延終了温度を８５０℃、巻き取り温度を６００℃とする熱間圧延を施し、板厚３．０ｍｍの熱延板とした。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℃の範囲で最大２分間、加熱処理し焼鈍板（冷延鋼板）を作製した。 Steels A to H having the composition shown in Table 1 are melted by a conventional steelmaking process, continuously cast into a slab, and then the slab is reheated to 1250 ° C., and the finish rolling finish temperature is set. Hot rolling was performed at 850 ° C. and a coiling temperature of 600 ° C. to obtain a hot rolled sheet having a thickness of 3.0 mm. The hot-rolled sheet was pickled and then cold-rolled to a plate thickness of 1.5 mm to obtain a test material. This test material was heat-treated in a nitrogen atmosphere containing 10 vol% of hydrogen in a range of 800 to 850 ° C. for 2 minutes at maximum using a laboratory reduction heating simulator to prepare an annealed plate (cold rolled steel plate).
　上記により得られた焼鈍板（冷延鋼板）に対して、硫酸亜鉛七水和物：１ｍｏｌ／Ｌを含有し、硫酸を用いて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を付着させた。Ｚｎの付着量は、電流密度と通電時間を変えることで変化させた。電気めっきを施した後のサンプルは、水洗した後、さらに二リン酸ナトリウム（Ｎａ４Ｐ２Ｏ７・１０Ｈ２Ｏ）水溶液に３秒間浸漬させた。溶液はＰ濃度として０．５ｇ／Ｌ、温度：５０℃を基準とし、一部では濃度と温度を変化させて評価も行った。なお、比較のため、電気めっきを施さず表面にＺｎを付着しない焼鈍板（冷延鋼板）も準備した。 With respect to the annealed plate (cold rolled steel plate) obtained as described above, an iridium oxide plate is used for the anode using an aqueous solution containing zinc sulfate heptahydrate: 1 mol / L and adjusted to pH 2.0 using sulfuric acid. Was used for electroplating to deposit Zn on the surface. The amount of Zn deposited was varied by changing the current density and the energization time. Sample after subjected to electroplating, after washed with water and immersed for 3 seconds disodium phosphate (Na 4 P 2 O 7 · 10H 2 O) solution. The solution was evaluated with a P concentration of 0.5 g / L and a temperature of 50 ° C. with some changes in concentration and temperature. For comparison, an annealed plate (cold rolled steel plate) that was not electroplated and did not adhere Zn to the surface was also prepared.
　次に、以上により得られた冷延鋼板に対して、以下に示す化成処理を実施した。 Next, the following chemical conversion treatment was performed on the cold-rolled steel sheet obtained as described above.
　まず、市販のアルカリ脱脂液（日本パーカライジング（株）製、ファインクリーナーＦＣ−Ｅ２００１）を規定濃度で建浴した場合と、劣化した場合を想定して規定濃度の２倍に希釈して建浴した場合のそれぞれにおいて、冷延鋼板を２分間浸漬し、水洗後の鋼板の水濡れ率を評価した。水濡れ率が８０％以上のものを○、８０％に満たないものを△、５０％以下のものを×とし、脱脂性の指標とした。 First, a commercially available alkaline degreasing liquid (manufactured by Nihon Parkerizing Co., Ltd., Fine Cleaner FC-E2001) was built at a specified concentration and diluted to twice the specified concentration assuming a deterioration. In each case, the cold-rolled steel sheet was immersed for 2 minutes, and the water wettability of the steel sheet after water washing was evaluated. A sample having a water wettability of 80% or more was evaluated as “◯”, a sample having less than 80% as “Δ”, and a sample having a water wettability of 50% or less as “×”.
　次に、前述した規定濃度の２倍に希釈した脱脂液で脱脂した冷延鋼板を、表面調整液（日本パーカライジング（株）製、ＰＬ−ＺＴＨ）に浸漬し、リン酸塩処理液（日本パーカライジング（株）製、パルボンドＰＢ−Ｌ３０８０）に、浴温：４３℃、処理時間：１２０秒の条件で浸漬し化成処理を行った。 Next, the cold-rolled steel sheet degreased with the degreasing liquid diluted to twice the specified concentration described above is immersed in a surface conditioning liquid (manufactured by Nihon Parkerizing Co., Ltd., PL-ZTH), and a phosphate treatment liquid (Nippon Parkerizing). Chemical conversion treatment was performed by dipping in Palbond PB-L3080 manufactured by Co., Ltd. under conditions of bath temperature: 43 ° C. and treatment time: 120 seconds.
　化成処理後の冷延鋼板表面を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、化成処理評点として以下の５段階で評価した。
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。 The surface of the cold-rolled steel sheet after the chemical conversion treatment is observed with a SEM at 10 magnifications at a magnification of 300 times. Evaluation was made according to the following five grades.
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.
　化成処理後の鋼板は、さらに、市販のＥＤ塗装（関西ペイント（株）製、ＧＴ−１０）を塗膜厚：２０μｍにて施し、塗装面にＮＴカッター（登録商標）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。以上により得られた結果を条件と併せて表２~５に示す。 The steel plate after the chemical conversion treatment was further applied with a commercially available ED coating (manufactured by Kansai Paint Co., Ltd., GT-10) at a coating thickness: 20 μm, and a cross cut was put on the coated surface with an NT cutter (registered trademark). Then, it was immersed in warm salt water (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. The results obtained as described above are shown in Tables 2 to 5 together with the conditions.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000005
　表２~５より、鋼Ａ、ＢおよびＣについては、鋼板成分にＳｉを多く含んでいないため、表面に電気Ｚｎめっきを施さない例（比較例１~３）においても良好な化成処理性が得られているが、剥離幅が大きく塗装後耐食性が劣っている。 From Tables 2 to 5, steels A, B, and C do not contain much Si in the steel plate components, so that good chemical conversion treatment is possible even in the examples where the surface is not subjected to electro-Zn plating (Comparative Examples 1 to 3). Although obtained, the peel width is large and the corrosion resistance after coating is poor.
　比較例９、１０と本発明例１~８（鋼Ａ）、比較例１１、１２と本発明例９~１６（鋼Ｂ）、比較例１３、１４と本発明例１７~２４（鋼Ｃ）では、表面に電気Ｚｎめっきを付与していくと温塩水浸漬試験後の剥離幅が減少し、特に１００ｍｇ／ｍ２以上の付着量では剥離幅のレベルが低く安定し塗装後耐食性に優れていることが分かる。 Comparative Examples 9, 10 and Invention Examples 1-8 (Steel A), Comparative Examples 11, 12 and Invention Examples 9-16 (Steel B), Comparative Examples 13, 14 and Invention Examples 17-24 (Steel C) Then, when applying electroplated Zn to the surface, the peel width after the hot salt water immersion test decreases, and particularly at an amount of 100 mg / m 2 or more, the peel width level is low and stable, and the post-coating corrosion resistance is excellent. I understand that.
　鋼Ｄ~Ｈは、Ｓｉを多く含むことから、表面にＺｎめっきを施さない例（比較例４~８）においては、化成結晶にスケが認められ、特に、Ｓｉ量１．５％以上となるＧ、Ｈでは化成結晶がほとんど形成されていない評点１のレベルになった。 Since steels D to H contain a large amount of Si, in the examples (Comparative Examples 4 to 8) in which the surface is not plated with Zn, scaling is observed in the chemical crystals, and in particular, the Si amount is 1.5% or more. In G and H, it became the level of the grade 1 in which almost no chemical conversion crystal was formed.
　電気Ｚｎめっきを施した場合、Ｚｎ付着量が１００ｍｇ／ｍ２未満の例（比較例１５~２４）では、まだスケが見られる化成結晶のレベルであり十分でない。 In the case where the Zn electroplating is performed, in the examples (Comparative Examples 15 to 24) where the Zn deposition amount is less than 100 mg / m 2 , the level of chemical conversion crystals still showing scaling is not sufficient.
　Ｚｎ付着量が１００ｍｇ／ｍ２以上の例（本発明例２５~６４）では、いずれもスケのない化成結晶が得られ化成処理性に優れている。また、同時に温塩水浸漬試験後の剥離幅も低く安定しており、鋼成分の影響をほとんど受けていないことが分かる。 In the examples where the Zn deposition amount is 100 mg / m 2 or more (Examples 25 to 64 of the present invention), chemical conversion crystals without any scale are obtained and the chemical conversion properties are excellent. At the same time, the peel width after the hot salt water immersion test is low and stable, indicating that the steel component is hardly affected.
　また、電気Ｚｎめっき後に、Ｐを含有する水溶液に接触させない例（比較例２５）や、Ｐを含有する水溶液に接触させても、そのＰ濃度が低い例（比較例２６、２７）、温度が低い例（比較例２８、２９））では、規定濃度に建浴した脱脂液では十分な脱脂性が得られるものの、実際の塗装ラインでの劣化状態を模擬した規定濃度の２倍に希釈した脱脂液で脱脂では脱脂後に水はじきが発生していた。 In addition, an example in which the P concentration is low even after contact with an aqueous solution containing P (Comparative Example 25) or an aqueous solution containing P after the electro-Zn plating, and the temperature is low. In low examples (Comparative Examples 28 and 29), a degreasing solution built to a specified concentration provides sufficient degreasing properties, but degreasing diluted to twice the specified concentration simulating a deterioration state in an actual coating line. In the case of degreasing with liquid, water repelling occurred after degreasing.
　これに対して、Ｐ濃度および処理液温度が本発明範囲内にある例（本発明例６５~６９、７０）では、希釈脱脂液においても十分な脱脂性が得られた。 On the other hand, in the examples where the P concentration and the treatment liquid temperature are within the scope of the present invention (Invention Examples 65 to 69, 70), sufficient degreasing properties were obtained even in the diluted degreasing liquid.
　Ｓｉなどの強化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、例えば、自動車ボディー用途として最適である。 Even in a high-tensile cold-rolled steel sheet containing a large amount of strengthening elements such as Si, the chemical conversion treatment property before coating is good and the corrosion resistance after coating is also good.

Claims (2)

  1. 　冷延鋼板表面にＺｎの付着量が１００~５０００ｍｇ／ｍ２となるように電気Ｚｎめっきを施し、水洗した後に、Ｐを含有し、前記Ｐの濃度が０．００１~２ｇ／Ｌであり、温度が３０~６０℃の範囲である水溶液に前記冷延鋼板を接触させることを特徴とする化成処理性および塗装後耐食性に優れた冷延鋼板の製造方法。 After electroplating Zn so that the amount of Zn deposited on the cold-rolled steel sheet surface is 100 to 5000 mg / m 2 and washing with water, it contains P, and the concentration of P is 0.001 to 2 g / L, A method for producing a cold-rolled steel sheet having excellent chemical conversion property and post-coating corrosion resistance, wherein the cold-rolled steel sheet is brought into contact with an aqueous solution having a temperature in the range of 30 to 60 ° C.
  2. 　冷延鋼板表面にＺｎの付着量が１００~１０００ｍｇ／ｍ２となるように電気Ｚｎめっきを施し、水洗した後に、
    Ｐを含有し、前記Ｐの濃度が０．００１~２ｇ／Ｌであり、温度が３０~６０℃の範囲である水溶液に前記冷延鋼板を接触させることを特徴とする化成処理性および塗装後耐食性に優れた冷延鋼板の製造方法。     After applying electric Zn plating so that the adhesion amount of Zn is 100 to 1000 mg / m 2 on the cold rolled steel sheet surface,
    After the chemical conversion treatment and coating, the cold-rolled steel sheet is brought into contact with an aqueous solution containing P, the concentration of P being 0.001 to 2 g / L, and the temperature being in the range of 30 to 60 ° C. A method for producing a cold-rolled steel sheet having excellent corrosion resistance.
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