JP2000328220A - Galvanized steel sheet and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a galvannealed steel sheet which is free of the damage of plating layers at the time of pressing and is overall excellent in formability, chemical conversion treatability, etc. SOLUTION: The galvanized steel sheet has films consisting of zinc oxide, zinc carbonate and zinc hydroxide on the plating layer surfaces at >=50 mg/m2 in total in terms of zinc. The steel sheet may be easily produced by bringing a solution containing 0.5 to 100 g/liter Zn ions and 0.05 to 5 wt.% hydrogen peroxide and having a pH 4.5 to 7 and bath temperature <=45 deg.C into contact with the galvanizing layers, then blowing gas containing carbon dioxide thereto. The contact of the carbon dioxide of the gas to be blown is more preferably specified to >=0.1 vol.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a galvanized steel sheet excellent in press formability and suitable for use as a material for automobiles, home appliances, buildings and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Galvanized steel sheets are inexpensive materials having excellent corrosion resistance, and thus are used in large quantities as materials for automobiles, home electric appliances, buildings and the like. Among them, alloyed hot-dip galvanized steel sheet has excellent properties such as chemical conversion treatment, paintability, weldability and adhesiveness as a coating base in addition to corrosion resistance. It is used.

When the surface of the plating layer is pure zinc or when it is a zinc alloy phase (ζ phase) having a low Fe content even if it is an alloyed hot-dip galvanized layer, the surface of the plating layer is soft. When a zinc-coated steel sheet is press-formed, an adhesion phenomenon occurs between the plating layer and the surface of the press die, which deteriorates the sliding property of the steel sheet, and easily causes a plating peeling phenomenon (flaking) and a press crack. There is a problem.

On the other hand, in the case of an alloyed hot-dip galvanized layer having a large Fe content in the plated layer, a hard alloy phase (Γ phase, Γ ₁ phase, δ _1c phase, etc.) is formed near the steel sheet / plating interface. Then, powdering (powdering) of the plating layer is likely to occur during press molding. When powdering occurs, a strip of plating adheres to the mold and causes indentation flaws. Therefore, when press-forming a galvanized steel sheet, particularly an alloyed hot-dip galvanized steel sheet, there is a demand for an improvement measure that does not cause these problems.

[0005] In order to solve such problems, metal contact between a mold and a plating layer is prevented by a method such as further applying metal plating to the surface of the plating layer or attaching various oxides. Further, there is disclosed a technique in which a press oil and a metal soap are formed to prevent the adhesion phenomenon between the plating layer and the mold, and to improve the slidability between the mold and the plating layer.

[0006] JP-A-3-287784, zinc oxide 3~500mg / m ² as zinc, Mn oxide 5 to 500 mg / m ^2, phosphate and Mo oxide as Mn, W oxide, One or more of V oxides are P, M
There is disclosed an alloyed hot-dip galvanized steel sheet having excellent press formability, chemical conversion property, and weldability provided with a coating made of an oxide containing 1000 mg / m ² or less as o, W or V on the surface.

[0007] JP-A-4-202786 and JP-A-4-202787 disclose a method for producing a plated steel sheet in which an iron-based alloy electroplating layer is formed on a galvannealed layer. These are methods in which an electroplating layer having fine irregularities on the surface is provided as an intermediate plating layer on the alloyed hot-dip galvanized layer, and iron-based alloy electroplating is performed thereon. Accordingly, it is an object of the present invention to prevent the plating layer from being cracked easily at the time of press forming, and to improve the electrodeposition coating property and the formability.

Japanese Patent Application Laid-Open No. 3-291366 discloses a steel sheet which has been subjected to hot dip galvanizing and alloying treatment using hydrogen peroxide:
By contacting with an aqueous solution containing 0.01 to 5% by weight, Fe ³⁺ : 0.01 g / liter or more and having a pH of 4 or less, an oxide film is formed on the surface of the plating layer to form spot weldability and chemical conversion. A method for producing an alloyed hot-dip galvanized steel sheet that improves processability is disclosed.

Japanese Patent Application Laid-Open No. 8-158066 discloses a galvanized steel sheet provided with an Fe—Ni—O-based coating on a zinc-based plating layer. This film has an adhesion amount of 10 to 1500 in terms of the total amount of metal elements in the film.
mg / m ² , with a film containing 0.5 to 30% oxygen.

[0010]

However, the post-treatment methods disclosed so far for imparting lubricity to galvanized steel sheets have the following problems and have not always been satisfactory.

If the purpose is only to improve the slidability of the galvanized layer, a film having a good compatibility with the press oil, for example, N
Provide a plating layer surface with a film containing i, Mn oxides, S compounds such as sulfurized oils and fats which have a proven track record as extreme pressure additives, Cl compounds such as chlorinated paraffin, and Ca compounds such as zinc calcium phosphate. There is a way.

However, since the steel sheets having these coatings have not been sufficiently used in automobile outer layer applications, careful prior evaluation is required before practical use.
In other words, when these steel sheets are put into practical use, the chemical conversion performance,
Adhesive performance by adhesive, corrosion resistance under various environments, etc.
It is necessary to strictly confirm the performance under a wide range of conditions, and an actual vehicle test may be required as the final evaluation. These evaluations require a great deal of expense and a long period of time to determine the evaluation results and reach the practical stage.

Further, the steel sheet described in Japanese Patent Application Laid-Open No. 3-287784 has a problem that a part of the metal oxide is dissolved during the chemical conversion treatment and the chemical conversion treatment liquid is contaminated. JP 4
In the manufacturing methods described in JP-A-202786 and JP-A-4-202787, it is necessary to provide a plurality of electroplating layers after hot-dip plating, so that the manufacturing cost is high. In the manufacturing method described in JP-A-3-291366, hydrogen peroxide is consumed and the solution life is shortened due to the influence of Fe ²⁺ eluted from the plating film, and the operability during oxide formation is significantly reduced. was there. The steel sheet disclosed in Japanese Patent Application Laid-Open No. 8-158066 is obtained by heating in an oxidizing agent or a mixed atmosphere of air and ozone to adjust the oxygen content. There is a problem that the manufacturing cost is increased due to an increase in the number of steps required for the heat treatment.

An object of the present invention is to solve the above-mentioned problems, to provide an alloyed hot-dip galvanized steel sheet which is free from surface damage during press working, and has excellent overall formability and chemical conversion properties. It is to provide a manufacturing method.

[0015]

Means for Solving the Problems Zinc oxide mainly composed of zinc oxide is conventionally present on the surface of a galvanized steel sheet which has been established for its quality as a material for automobiles. It has been well demonstrated that they do not adversely affect the adhesion or adhesion. Therefore, when a coating mainly composed of zinc oxide is provided on the surface of the plating layer, there is an advantage that a long-term test such as an actual vehicle test can be simplified when the performance of the plated steel sheet is finally confirmed.

From such a viewpoint, the present inventors have proposed a zinc compound mainly composed of zinc oxide as a post-treatment for improving the slidability without deteriorating performance other than press-formability such as chemical conversion property and adhesiveness. Focusing on the usefulness of the coating, we studied in detail how to provide the desired zinc compound at low cost without requiring equipment modification.

When the plating layer is immersed in a solution containing an oxidizing agent, the oxidizing agent is reduced by elution of the plating film, the pH rises at the solid-liquid interface, and a stable zinc oxide film mainly composed of zinc oxide is formed on the surface. It is formed. Moreover, the liquid film adhering to the surface of the plating layer pulled up from the solution contains a large amount of Zn ions contributing to the formation of a zinc compound. By spraying a gas containing carbon dioxide gas on the liquid film on the surface of the plating layer, Zn ions in the liquid film are fixed on the plating surface as zinc carbonate, and a film having a desired adhesion amount is provided by a short immersion treatment. be able to. The coating usually also contains zinc hydroxide.

According to this method, it is possible to obtain a good coating treatment which has proved press formability, chemical conversion property, electrodeposition coating property, etc., and also has an advantage that the liquid life is long, stable production is possible, and the cost is low. There is.

In this method, the elution of Fe contained in the plating layer is suppressed by suppressing the dissolution of the plating layer by setting the pH of the treatment solution to a neutral region, and the consumption of the oxidizing agent in the solution is suppressed. Therefore, the life of the solution can be kept long.

The present invention has been completed on the basis of these findings, and its gist is as follows: (1) a zinc-coated steel sheet having excellent press formability; and (2) and (3). In its manufacturing method.

(1) On the surface of the plating layer, a film composed of zinc oxide, zinc carbonate, and zinc hydroxide is used as zinc for a total of 5
A galvanized steel sheet excellent in press formability, characterized by having 0 mg / m ² or more.

(2) Zn ions:
0.5 to 100 g / liter, hydrogen peroxide: 0.05% to 5
% By weight, a solution having a pH of 4.5 to 7 and a bath temperature of 45 ° C. or lower is brought into contact with the zinc-based plating layer, and then a gas containing carbon dioxide gas is blown to oxidize the surface of the plating layer. A method for producing a galvanized steel sheet, comprising a total of 50 mg / m ² or more of a film composed of zinc, zinc carbonate, and zinc hydroxide as zinc.

(3) The method for producing a galvanized steel sheet according to the above (2), wherein the carbon dioxide content of the gas to be sprayed is 0.1% by volume or more.

[0024]

Embodiments of the present invention will be described below in detail. In addition,% display showing a chemical composition means weight% unless there is particular notice.

[0025] Plating base material: The type of the steel sheet used as the plating base material is not particularly limited, but known cold-rolled steel sheets and hot-rolled steel sheets are suitable. The chemical composition of the base material is Ti, N
ultra-low carbon steel, low carbon steel, or Si, Mn, P, Cr, Ni, C
Alloy steel containing u, Ti, Nb, V, or the like as appropriate can be used.

Plating layer: The plating layer may be a known zinc-based plating layer, and the plating metal species is Fe, A, in addition to Zn.
1, Mg, Ni, Cr, Si, Mn, Pb, Sb, Sn
And zinc-based alloy plating containing one or more of the group consisting of misch metal. The plating method is optional, and may be a known method such as hot-dip plating, electroplating, vapor deposition plating, and electroless plating. Among them, hot-dip plating is preferred because it is inexpensive.

In the case where the plating layer is formed by hot-dip galvanizing with an Fe—Zn alloy, the Fe content of the plating layer is preferably set to 8 to 15% with respect to the weight of the plating layer. Fe content is 8
%, It is highly possible that the ζ phase remains near the surface of the plating layer. The ζ phase is not preferable because coarse columnar crystals are easily formed, the surface of the plating layer becomes rough, and the press formability of the plated steel sheet may be impaired. It is more preferably at least 9%. If the Fe content exceeds 15%, powdering is likely to occur during press molding, which is not preferable. It is more preferably at most 12%.

Al is 0.05 to 0.15% in the plating layer.
It is good to contain. This is effective in suppressing the formation of an alloy layer at the interface with the base material when the base material is immersed in the hot-dip galvanizing bath.

The effect of improving the press formability is obtained as the amount of the coating of zinc oxide, zinc carbonate and zinc hydroxide on the surface of the plating layer increases. It is particularly good when the total amount of zinc is 50 mg / m ² or more. Therefore, in the zinc-based plated steel sheet of the present invention, the surface of the plated layer is provided with a zinc compound composed of zinc oxide, zinc carbonate and zinc hydroxide in a total amount of 50 mg / m ² or more as zinc. Preferably it is 100 mg / m ² or more.

Further, the effect of improving press formability is particularly good when the content of zinc carbonate in the zinc compound is 5 mg / m ² or more as zinc. Zinc hydroxide is formed in the process of bringing the plating layer into contact with an aqueous solution containing an oxidizing agent, and is effective in promoting the formation of a zinc compound. The presence of zinc carbonate and zinc hydroxide can be confirmed by a thin film X-ray method.

The galvanized steel sheet of the present invention is preferably manufactured by the following method. For the base material, hot-dip plating,
Plating is performed by a known method such as an electroplating method, a vapor deposition plating method, and an electroless plating method. The plating surface may be either both surfaces of the base material or only one surface. The coating amount of plating is optional, but is preferably 30 to 150 g / m ² per one surface from the viewpoint of easy control of the coating amount and suppression of powdering.

Treatment solution: 0.5 to 100 g / l of Zn ions and 0.05 of hydrogen peroxide were added to the above zinc-based plating layer.
A solution (treatment liquid) containing 〜5% by weight and having a pH of 4.5-7 is brought into contact.

The Zn ion content in the treatment liquid is 0.5 g /
If the amount is less than 1 liter, the formation of a zinc compound on the surface of the plating layer becomes insufficient, and the slidability of the plating layer cannot be sufficiently improved. Therefore, the Zn ion content is set to 0.5 g / liter or more, preferably 2 g / liter or more. If the Zn ion content exceeds 100 g / l, the effect of improving the slidability is saturated and the cost is increased, which is not preferable. For this reason, the Zn ion content is set to 100 g / liter or less.
Preferably it is 50 g / liter or less.

When the concentration of hydrogen peroxide is less than 0.05%, formation of a zinc compound on the surface of the plating layer becomes insufficient, and the sliding property of the plating layer cannot be sufficiently improved. Therefore, the concentration of hydrogen peroxide is set to 0.05% or more. Preferably it is 0.1% or more. If the concentration of hydrogen peroxide exceeds 5%, the effect of improving the slidability is saturated, and the cost increases, which is not preferable. Therefore, the concentration of hydrogen peroxide is set to 5% or less. Preferably it is 2% or less.

The content of Zn ions is Zn (SO ₄ ) ·
It can be easily adjusted by the addition amount of a Zn ion source such as 7H ₂ O and ZnCl ₂ to the processing stock solution.

When the plating layer containing several percent of Fe elutes, the Fe in the plating layer elutes as Fe ²⁺ , reacts with hydrogen peroxide, consumes hydrogen peroxide excessively, and shortens the life of the processing solution. . In order to extend the life of the processing solution, it is necessary to minimize elution of the plating layer when the plating layer is brought into contact with the processing solution. Therefore, the pH of the treatment liquid is set to 4.5 or more, preferably pH: 5.0 or more. If the pH exceeds 7, the oxidizing property of hydrogen peroxide increases, and an auto-oxidation reaction occurs to shorten the life of the processing solution. Therefore, the pH of the processing solution is set to 7 or less.

In controlling the pH of the processing solution, it is preferable to avoid adding an acid alone. It is important that the sulfates and chloride ions, which are strong acid salts, are not added unless they are mixed as a supply source of Zn ions. The temperature of the treatment liquid is preferably 45 ° C. or lower, more preferably 40 ° C. or lower.

The method of bringing the treatment liquid into contact with the plating layer is not particularly limited, and may be a method of dipping the plating layer in the treatment liquid (immersion method), a method of spraying the plating layer with the treatment liquid (spray method) or a treatment. Any method such as applying the liquid with a roll coater may be used.

After the treatment liquid is brought into contact with the plating layer, a gas containing carbon dioxide gas is blown onto the treatment liquid film adhering to the plating layer surface, and CO ions are added to the Zn ions dissolved in the liquid film.
₂ is contacted to form zinc carbonate with zinc oxide.
In order to promote the generation of zinc carbonate, the gas to be sprayed preferably has a carbon dioxide gas concentration of 0.03% by volume or more.

When the concentration of carbon dioxide gas is 0.1% by volume or more, the fixing rate as zinc carbonate is increased, and the slidability is remarkably improved. The carbon dioxide gas concentration may be 100%.

Since the atmosphere usually contains about 0.033% by volume of carbon dioxide, air can be used as the gas to be blown onto the processing liquid. In order to increase the concentration of carbon dioxide gas above the atmosphere, it is effective to use, for example, combustion exhaust gas discharged from a heating furnace or the like. A mixed gas of nitrogen gas and carbon dioxide gas may be used.

The treatment after the above-mentioned gas is blown onto the treatment liquid remaining in the plating layer may be arbitrarily performed. For example, the subsequent washing and drying may be performed by a commonly used method.

[0043]

EXAMPLES C: 0.004%, Si: 0.01%, M
n: 0.25%, P: 0.01%, S: 0.01%, T
i: A 0.7 mm-thick ultra-low carbon Ti-added steel sheet containing 0.035% was used as a base material, and the attached amount was 6 per side.
A hot-dip galvanized steel sheet (GI) was produced by performing hot-dip galvanizing at 0 g / m ² . Further, this was heated to 500 ° C. to prepare an alloyed hot-dip galvanized steel sheet (GA) comprising 9% of Fe and the balance being Zn. Also, cold-rolled steel sheets of the same chemical composition are degreased, pickled and then galvanized,
An electrogalvanized steel sheet (EG) having an adhesion amount of 45 g / m ² per side was produced. The electroplating bath is zinc sulfate: 20
Containing 0 g / l, 30 g / l ammonium sulfate,
Plating was performed at an electric density of 20 A / dm ² using a plating bath having a pH of 3 and a bath temperature of 45 ° C. A part of the electrogalvanized steel sheet was heated to 300 ° C. to produce an alloyed electrogalvanized steel sheet (EGA) having a Zn—Fe alloy plating film with an Fe content of 15%. Many 100 mm square test pieces were sampled from these plated steel sheets.

An aqueous solution containing Zn ions and hydrogen peroxide at various ratios was prepared as a treatment liquid, one liter at a time. The Zn ion content of the treatment liquid was adjusted using zinc sulfate and zinc chloride. The concentration of hydrogen peroxide was adjusted by adding a predetermined amount of a commercially available aqueous solution containing 30% of hydrogen peroxide. As a comparative example, when lowering the pH of the treatment liquid to less than 4.5, the pH was adjusted using 98% sulfuric acid. The test piece was immersed in the treatment liquid for 15 seconds, pulled up, and sprayed with a gas having a pressure of 0.05 kg / cm ² . As the gas, an atmosphere in which the concentration of carbon dioxide was changed or nitrogen gas containing no carbon dioxide was used. After spraying the gas, it was washed with tap water for 30 seconds and dried in the atmosphere.

The amount of the coating consisting of zinc oxide, zinc carbonate, and zinc hydroxide on the test piece was determined using Br ₂ -CH ₂
Immersion in an aqueous solution (temperature is room temperature) containing 0.5% by weight of ₃ OH to dissolve the plating layer, separate the residue, redissolve it with hydrochloric acid, and analyze it by ICP spectroscopy Obtained. A case where the amount of deposit was 50 mg / m ² or more as zinc was judged to be good.

The amount of zinc carbonate deposited was confirmed by the following method. Aqueous solutions having various zinc carbonate concentrations were applied to a cold-rolled steel sheet having the same level of surface roughness as a plated steel sheet by a bar coater method, and dried to prepare steel sheet samples to which various ranges of zinc carbonate had adhered. The deposits on the sample surface were dissolved in a 10% hydrochloric acid solution containing an inhibitor, and the resulting solution was analyzed by ICP spectroscopy to measure the amount of Zn deposition.
Further, the surface of the same sample was examined by a thin film X-ray method with an inclination angle of 2 °, and the peak intensity of the (104) plane of zinc carbonate was measured. A calibration curve for estimating the amount of Zn attached from the (104) plane peak intensity by the thin film X-ray method was prepared from the measured values of both. The (104) plane peak intensity on the surface of the test piece was measured by a thin film X-ray method, and the amount of zinc carbonate deposited on the surface of each test piece was determined using the above calibration curve.

The slidability of the plated steel sheet was evaluated by the coefficient of friction between the plated steel sheet and the mold when the steel sheet was U-formed using the high surface pressure U forming test apparatus shown in FIG.

In FIG. 1, reference numeral 1 denotes a test piece, 2 denotes a die, 5 denotes a punch, 4 denotes a bead, and 6 denotes a wrinkle holder. Test piece 1
Is placed on the surface of the die 2, and various wrinkle holding forces are applied to the test piece 1 via the beads 4 provided on the lower surface of the wrinkle holder 6 to press the test piece 1 against the die surface and lower the punch 5. The test piece 1 is formed into a U shape by pushing the test piece 1 into the die groove 3. A commercially available rust preventive oil was applied to both sides of the test piece 1 at a rate of ² g / m ² , the pressing speed of the punch 5 was 60 mm / min, and the wrinkle pressing force (P) was 750 to 750.
The forming force (F) applied to the punch 5 when U-forming was performed with various changes in the range of 1500 kgf was measured, and the coefficient of friction (μ) between the steel sheet surface and the tool was determined from the change in forming force accompanying the change in wrinkle holding force. ) Was evaluated, and the sliding property of the plating layer was evaluated based on the magnitude. A case where the friction coefficient was 0.23 or less was judged to be good.

The life of the treatment solution was determined by measuring the total amount of zinc oxide in the test piece (first sheet) immersed immediately after bathing and in the test piece immersed in 200 sheets after bathing. A case where the adhesion amount was 90% or more of the first sheet was judged to be good.

Table 1 shows the test conditions, the coefficient of friction of the plated steel sheet, and the results of measuring the service life of the treatment solution.

[0051]

[Table 1]

As can be seen from Table 1, the steel sheet satisfying the conditions specified by the present invention had a low coefficient of friction and exhibited good slidability. Further, the total amount of zinc oxide deposited on the steel sheet treated under the condition range specified by the present invention has a desired amount of zinc oxide containing zinc carbonate in all of the 200 sheets to be treated, and the lifetime of the treatment solution All were good. On the other hand, in Test Nos. 1, 9, 19 and 20, in which the amount of zinc oxide attached was less than 50 mg / m ² , the coefficient of friction was high. Test Nos. 1 and 9 are those in which the Zn ion concentration or hydrogen peroxide concentration of the treatment solution was too low.
No. 9 is a sample in which no gas was blown.
Is sprayed with a nitrogen gas containing no carbon dioxide gas. In Test Nos. 14 and 15, the pH of the treatment liquid was 4.5.
And the liquid life was short. Test number 16
Is the case where the pH of the processing liquid exceeds 7, but the liquid life was short due to the auto-oxidation phenomenon of hydrogen peroxide.

[0053]

EFFECT OF THE INVENTION The zinc-coated steel sheet of the present invention has good sliding properties because it has zinc carbonate or a sufficient amount of zinc oxide containing zinc carbonate and zinc hydroxide in addition to zinc oxide on the surface. And excellent press workability. The steel sheet having the zinc oxide of the present invention can be easily and inexpensively manufactured by using a treatment liquid having a specific composition and a gas containing carbon dioxide gas. Since the treatment liquid has a long life and good operability and can be manufactured at low cost, it is suitable as a material for automobiles, home electric appliances, buildings and the like.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an outline of a test apparatus used for a high surface pressure U-shaped forming test.

[Explanation of symbols]

1: test piece, 2: die, 3: die groove, 4: bead,
5: punch, 6: wrinkle control.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C23C 28/00 C23C 28/00 C C25D 5/26 C25D 5/26 F 5/48 5/48 (72) Inventor Kazushi Ishigaki 4-53, Kitahama, Chuo-ku, Osaka City F-term in Sumitomo Metal Industries, Ltd. (reference) 4K024 AA05 BA03 BB02 BB15 BB18 BC01 DB01 DB03 GA08 4K026 AA07 AA12 AA13 AA22 BA08 BB09 CA13 CA18 CA35 CA36 DA02 DA03 DA06 DA11 4K027 AA02 AA22 AB02 AB26 AB28 AB42 AC73 AC82 AE23 4K044 AA02 AB02 BA10 BA12 BB03 BC05 CA11 CA18 CA53 CA62

Claims (3)

[Claims] 1. A coating comprising zinc oxide, zinc carbonate and zinc hydroxide on the surface of a plating layer in a total of 50 as zinc.
A zinc-based plated steel sheet having excellent press formability, characterized in that it is provided with at least mg / m ² . 2. The zinc-based plating layer has a Zn ion content of 0.5.
-100 g / liter, hydrogen peroxide: 0.05% -5% by weight
And a solution having a pH in the range of 4.5 to 7 is contacted, and a gas containing carbon dioxide gas is sprayed on the surface of the plating layer to form a film made of zinc oxide, carbonic acid oxidized and zinc hydroxide on the surface of the plating layer. A method for producing a galvanized steel sheet having excellent press formability, characterized in that a total of 50 mg / m ² or more is provided. 3. The sprayed gas has a carbon dioxide content of 0.1.
The method for producing a galvanized steel sheet excellent in press formability according to claim 2, wherein the content is 1% by volume or more.