JPH08296057A - Galvanized steel sheet excellent in pressability, chemical convertibility and degreasing liquid contamination resistance - Google Patents

Abstract

PURPOSE: To prevent the elution of an inorg. oxide in chemical conversion treatment such as degreasing by forming the inorg. oxide on the surface and treating a galvanized steel sheet excellent in pressability, chemical convertibility, etc., with a curing promoter. CONSTITUTION: The oxide layer of Mn, Mo, P, Co, Ca, Ni, W, V, B, etc., is formed on a steel sheet plated with pure Zn or Zn alloy at 1mg/m<2> , for example, to improve the pressability and chemical convertibility of the galvanized steel sheet. A rust preventive oil is applied on the sheet surface when shipped, the oil is removed when the sheet is used, and the sheet is press-formed and so on. The inorg. oxide-coated steel sheet is brought into contact with a curing promoter such as nitrous acid and phosphorous acid to cure the inorg. oxide. Consequently, the inorg. oxide is not eluted into a degreasing liq., the press-formability is not lowered, the degreasing liq. is not contaminated with the inorg. oxide, and the degreasing function is not deteriorated. Further, the cured inorg. oxide is not dissolved in the degresing liq., and the increase in the cost and lowering of productivity due to the replacement of the contaminated degreasing liq. are prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a galvanized steel sheet which is excellent in pressability, chemical conversion treatment property and degreasing liquid stain resistance.

Japanese Unexamined Patent Publication No. 4-176878 discloses that a zinc-based plated steel sheet having excellent pressability and chemical conversion treatability is produced by forming an inorganic oxide on the surface of the zinc-based plated steel sheet. Such surface-treated steel sheet has improved press formability as compared with cold-rolled steel sheet, there is no flaw during forming, and there is no peeling of inorganic oxide due to pressing, etc. Is also excellent. It is also disclosed that ZnO oxide is generated to improve weldability.

[0003]

As described above, in the case of a zinc-based plated steel sheet on which an inorganic oxide is formed, the surface of the zinc-plated steel sheet is coated with rust-preventive oil and shipped. The surface of this zinc-based plated steel sheet is subjected to degreasing treatment for removing rust preventive oil prior to chemical conversion treatment such as bondage treatment. Then, during this degreasing treatment, a part of the inorganic oxide is eluted into the degreasing liquid to contaminate the degreasing liquid,
Since the degreasing function is deteriorated and the liquid needs to be replaced, the productivity is reduced by stopping the line, and the cost of the degreasing liquid is increased. The method of the present invention has been made in order to advantageously solve such a problem, and provides a method for reliably suppressing elution of the inorganic oxide to a degreasing liquid or the like, which is produced and coated on the surface of the zinc-plated steel sheet. The purpose is to do.

[0004]

The method of the present invention is characterized in that after an inorganic oxide is formed on the surface of a galvanized steel sheet, it is brought into contact with an aging accelerator-containing aqueous solution to remove the inorganic oxide. A method for producing a zinc-based plated steel sheet excellent in pressability, chemical conversion treatment property, and degreasing liquid stain resistance, which is characterized by aging.

Examples of zinc-based plated steel sheets which produce the above-mentioned inorganic oxides include those produced by various manufacturing methods such as hot dipping, electroplating, vapor deposition, and thermal spraying. Is pure Zn,
Zn and Fe, Zn and Ni, Zn and Al, Zn and Mn, Z
n and Cr, Zn and Ti, Zn and Mg such as Zn as a main component, or Fe for improving various functions such as corrosion resistance,
Ni, Co, Al, Pb, Sn, Sb, Cu, Ti, S
i, P, etc., including one or more kinds of alloying elements and impurity elements, ceramic fine particles such as SiO ₂ , Al ₂ O ₃ , oxides such as TiO ₂ and BaCrO ₄ , organic materials such as acrylic resin. There are some in which the molecules are dispersed in the plating layer, and there are some in which the composition of a single composition changes continuously or in layers in the thickness direction of the plating layer. As a pure Z
In addition to n, Zn and Fe, Zn and Ni, Zn and Al, Zn and Mn, Zn and Cr, Zn and Ti, Zn and Mg, etc., containing Zn as a main component for improving various functions such as corrosion resistance, Includes two or more kinds of alloying elements and impurity elements, fine particles of ceramics such as SiO ₂ and Al ₂ O ₃ , Ti
There is one in which an oxide such as O ₂ or BaCrO ₄ or an organic polymer such as an acrylic resin is dispersed in the plating layer. For example, hot-dip galvanized steel sheet, vapor-deposited galvanized steel sheet, iron-zinc-zinc plated steel sheet, aluminum containing zinc as a main component, alloyed hot-dip galvanized steel sheet such as iron, and the lower layer is alloyed in the plating layer cross-section direction. Alloyed hot-dip galvanized steel sheet (generally referred to as half alloy), one-sided-zinc alloyed hot-dip galvanized layer, galvanized steel sheet consisting of the other side hot-dip galvanized layer, electroplating on these plating layers, zinc by vapor deposition plating, etc., Alternatively, a steel sheet containing zinc as a main component and plated with a metal containing iron or nickel, or an electrogalvanized steel sheet, an alloy electroplated steel sheet such as zinc, nickel, or chrome, or a single alloy layer or a multilayer alloy electroplated steel sheet, zinc And zinc-containing metal vapor-deposited steel sheets. In addition, there is a dispersion-plated steel sheet in which fine particles of ceramics such as SiO ₂ and Al ₂ O ₃ , fine particles of TiO ₂ oxide, and organic polymer are dispersed in zinc or zinc alloy plating. Further, there is a multi-layer plated steel sheet obtained by plating the surface of a plated steel sheet that does not contain zinc or does not contain zinc as a main component, such as an aluminum-plated steel plate, with zinc as a main component as described above.

As described above, examples of the inorganic oxides formed on the surface of the zinc-plated steel sheet include Mn, Mo, P,
It produces an oxide consisting of one or more of Co, Ca, Ni, W 2, V 3, and B 2. Such an oxide forms a glassy film similar to the chromate film, and suppresses galling of the plating on the die at the time of pressing to improve the slidability. Further, unlike the chromate film, it completely dissolves in the chemical conversion treatment liquid to form a uniform chemical conversion treatment film, and these film-forming components are also components of the chemical conversion treatment liquid and do not contaminate the chemical conversion treatment liquid. The structure of such an inorganic oxide is Mn, Mo, Co, C
Compound of a, Ni, W, V and Zn supplied to the film by etching the plating layer or oxide or hydroxide of the plating layer alloy element, phosphate, sulfate, nitrate, borate, etc. believed, is not clear Mn-O bond, other metals -O bond, P -O bond, in the network entity comprising a B -O bond, partially -OH, CO ₃ group and the like, and further plated It is presumed that the metal supplied from the layer may have a substituted amorphous macromolecular structure. Further, since such an oxide does not dissolve even in the washing process with oil and the degreasing process, the lubricating performance at the time of pressing is deteriorated and other processes are hardly loaded.

The formation of such an oxide on a zinc-based plated steel sheet can be surely produced by, for example, immersing the plated steel sheet in an aqueous solution or applying the aqueous solution by spraying. At this time, the alloy elements (metals) of the zinc-plated steel sheet and impurities in the aqueous solution are slightly mixed in the oxide, but this is not an obstacle. The elements that do not hinder the inclusion of Li, Be, C, F, N in the film.
a, Mg, Al, Si, Cl, K, Ca, Ni, Mo, V, W, Ti, F
e, Rb, Sr, Y, Zn, Nb, Cs, Ba, lanthanide ions, oxides, hydroxides, phosphates, sulfates, nitrates, etc. are mixed to some extent (less than about 10% in the film). Has no effect. Furthermore, if the amounts of Cr, Cd, Pb, Sn, and As are small, the chemical conversion treatment property and the contamination of the chemical conversion treatment liquid are not affected, and the effect of the present invention remains unchanged.

Next, the production range of the inorganic oxide is
The amount of metal should be 1 mg / m ^2, but if it exceeds 500 mg / m ² , it is not preferable because the dissolution of the coating becomes slow and the formation of the chemical conversion coating becomes unstable in the chemical conversion treatment performed by users of automobiles and home appliances. .

As the method for producing the above-mentioned inorganic oxide, for example, potassium permanganate, phosphoric acid, sodium borate, ammonium molybdate, phosphomolybdic acid, ammonium tungstate, phosphotungstic acid, silicotungstic acid, Chlorides of ammonium vanadate, cobalt, nickel, calcium, etc., 0.1 g / l as chlorides or sulfates, solubility limit, phosphoric acid, sulfuric acid, nitric acid, hydrochloric acid, fluorides, etc. were added to accelerate the reaction. A bath can be used.

As described above, in order to obtain a zinc-based plated steel sheet which produces an inorganic oxide on the surface of the plated layer of the zinc-plated steel sheet, improves pressability and chemical conversion treatment, and further improves weldability, Weldability can also be improved by forming an oxide mainly composed of ZnO 2 as described below on the surface of the plating layer and forming an inorganic oxide as described above on the upper layer thereof. As the oxide containing ZnO as a main component, the oxide may contain, in addition to ZnO, a compound such as an oxide such as a component element contained in the plating layer. Further, in the electrochemical treatment such as anodic oxidation, a component or compound contained in the treatment liquid may be contained.

Next, as a method of producing an oxide mainly composed of ZnO, a zinc-based plated steel sheet is brought into contact with an acid-containing oxidant aqueous solution to form an oxide mainly composed of ZnO.
It becomes easy to produce 30 to 3000 mg / m ² in an amount, and a zinc-based plated steel sheet with excellent weldability can be obtained. The function of acid is to slightly dissolve the surface of the plating layer and supply ions such as Zn from the plating layer, and also to increase the PH in the oxidant aqueous solution that comes into contact with the plating layer, and the oxidant is mainly ZnO on the surface of the plating layer. It has a function of promoting the generation of oxides. By containing, for example, HNO ₃ 10 to 100 g / l as an oxidizing agent, it is possible to oxidize Zn and the like to generate an oxide mainly composed of ZnO on the surface of the plating layer. Further, as an oxidizing agent, KMnO ₄ , Ca (ClO) ₂ , NaClO ₂ , ClO ₂ , KNO ₂ , NaNO ₂
It is possible to accelerate the production of oxides by adding such a compound.

Next, as a Zn ion replenisher for producing an oxide mainly composed of ZnO, for example, Zn (NO ₃ ) ₂ 100
By adjusting the amount to 600 g / l, the pH of the oxidant aqueous solution can be reduced to about 4 or less, and the Zn ions can be replenished sufficiently to contribute to the activation of the plating layer surface and generate an oxide mainly composed of ZnO. . By replenishing Zn ions in advance in this manner, it is not necessary to dissolve Zn ions from the plating layer to replenish (supply) them, and it is possible to precipitate an oxide mainly composed of ZnO in a shorter time, which is preferable. . Then, by dipping a zinc-based plated steel sheet in such an aqueous solution and contacting (applying) it for 0.2 to 10 seconds by spraying the aqueous solution, it is possible to reliably generate an oxide mainly composed of ZnO that improves weldability. it can.

As described above, in addition to the method of forming an oxide mainly composed of ZnO, for example, Zn (NO ₃ ) ₂ .6H ₂ O 400 g / l, HN
Current density in a solution of O ₃ 1 with a plated steel plate as the cathode
ZnO with excellent weldability at ~ 20A / dm ² and processing time of 0.5-10 seconds
It is possible to generate an oxide mainly composed of. Besides this,
When alloying a hot-dip galvanized steel sheet as described above, an air-water mixture gas is introduced in an alloying furnace to adjust the dew point for alloying, and an oxide mainly composed of ZnO is formed on the surface of the alloyed plating layer. Can also be generated. As described above, the lower limit of the amount of ZnO produced is 30 mg / m ² for ZnO, and if it is less than this, it becomes difficult to improve the weldability, and if it exceeds 3000 mg / m ² , the oxide content increases. Becomes a resistance film and may shorten the life of the welding electrode tip due to heating, which is not preferable.

In this way, the oxide mainly composed of ZnO is surely prevented from expanding the diameter of the electrode tip due to the adhesion of the plating metal (Zn) to the welding electrode tip in spot welding to prevent welding failure. In addition, the life of the electrode tip can be extended.

However, in a zinc-based plated steel sheet in which weldability does not need to be so important, the above-mentioned oxides mainly composed of ZnO are not formed on the surface of the plated layer of the zinc-based plated steel sheet, and By forming an inorganic oxide on the surface of the plating layer, a zinc-based plated steel sheet having excellent pressability and chemical conversion treatability can be obtained.

In this way, when the zinc-based plated steel sheet on which the inorganic oxide is formed is subjected to a chemical conversion treatment such as a bonder treatment, a chemical conversion film is uniformly formed and the adhesion of the coating film is improved uniformly. When the press-molding is continued, the slidability is improved by the inorganic oxide, the moldability comparable to that of the cold-rolled steel sheet can be secured, and the pressability and the like can be improved.
Further, the subsequent chemical conversion treatment film can be formed uniformly.

As described above, after the inorganic oxide is formed (coated), it is aged by contact with an aging accelerator. As a type of aging accelerator, for example, nitrous acid,
Phosphorous acid, hypophosphorous acid, sulfurous acid, oxalic acid and sodium,
There are inorganic reducing agents such as salts of potassium, ammonium, magnesium and the like, and organic reducing agents such as ascorbic acid, methanyl, ethanol, ethylene glycol, reducing sugar (dextrin) and formaldehyde. Such an aging accelerator can be used as a solution, and the inorganic oxide can be aged by contacting it by dipping, spraying, roll coating, or the like, and the aging accelerator is applied after the inorganic oxide is formed (coated). For example, an inorganic oxide may be formed (coated) and immediately applied and dried, or an inorganic oxide may be formed (coated) and dried and then applied, or an inorganic oxide may be formed (coated). It can also be applied by adding it to the rust preventive oil applied after drying. Therefore, one or two or more of the aging accelerators as described above can be mixed, and the mixed form can be used by dissolving in an aqueous solution or an oily liquid such as rust preventive oil, and the dissolving concentration is 0.01 to 5 % Is sufficient, and if it is less than 0.01%, the reduction of the inorganic oxide becomes insufficient, and it may elute during the degreasing treatment to contaminate the degreasing liquid, which is not preferable. If it exceeds 5%, the reducing effect is saturated, so it is not preferable to set it to 5% or less. The coating amount is 0.1
If it is cc / m ² or more, it can be often recovered and recycled. When the aging accelerator is not added to the rust preventive oil, the rust preventive oil is shipped after being contacted with the aging preventive agent, dried and then coated with rust preventive oil which is a usual process. When the aging accelerator is added to the rust preventive oil, an inorganic oxide is produced and dried, and then the inorganic oxide is aged and oiled at the same time by applying oil before shipment.

Thus, by bringing the inorganic oxide into contact with the aging accelerator, a dehydration condensation reaction (crosslinking reaction) and a reduction reaction of the compound with the inorganic oxide occur at the same time, so that the oxide is neutralized or alkaline. Since it is reduced to a sparingly soluble oxide, it is possible to reliably suppress the elution of inorganic oxides into the solution during degreasing after pressing and washing with water, and to prevent the chemical conversion treatment solution from being contaminated by the elution of oxides. Restrain and
The life of the degreasing liquid can be extended and the load of wastewater treatment can be reduced.

[0019]

EXAMPLES Next, examples of the method of the present invention will be given together with comparative examples. Tables 1 and 2 show examples and comparative examples in which an inorganic oxide is formed on the surface of the zinc-plated steel sheet and the oxide is aged, and Tables 3 and 4 show ZnO oxides on the surface of the zinc-plated steel sheet. Examples and comparative examples in which an inorganic oxide is formed on the surface thereof and then the inorganic oxide is aged will be shown.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

[Table 4]

Note 1) Types of galvanized sheet EG: Electrogalvanized steel sheet, AS: Alloyed hot-dip galvanized steel sheet (Fe 10%, Al 0.2%, residual Zn), GI: Hot-dip galvanized steel sheet, HA: Semi-alloyed Hot dip galvanized steel sheet (Fe
5%, Al 0.3%, residual Zn), Zn-Ni: zinc-nickel alloy electroplated steel sheet (Ni 9%, residual Zn), Zn
-Mg: Zinc magnesium alloy vapor deposition plated steel sheet (Mg1
0%, residual Zn), Zn-Cr: Zn-Cr alloy electroplated steel sheet (Cr 14%, residual Zn), Zn-Mn: Zn-M
n alloy electroplated steel sheet (Mn 20%, residual Zn), Zn-
Al: Zinc aluminum alloy hot-dip galvanized steel sheet (Al5
%, Mg 0.1%, residual Zn), Zn / Al-Zn: zinc upper layer aluminum zinc alloy hot dip plated steel sheet (upper layer Zn2
g / m ^2, the lower layer Al55%, residual Zn60g / m ^2), Z
n-Fe: Zinc-iron alloy electroplated steel sheet (Zn85%,
Fe15%), Zn-Cr-Ni: Zn-Cr-Ni alloy electroplated steel sheet (Zn85%, Cr13%, Ni2)
%), Zn / Al: zinc upper layer aluminum plated steel sheet (upper layer Zn 1 g / m ² , lower layer Al 60 g / m ² ). Normal steel with a steel plate thickness of 0.8 mm. Note 2) ZnO oxide generation method-Immersion: Zn (NO ₃ ) ₂・ 6H ₂ O 400g / l, HNO ₂ 70g / l The alloyed hot dip galvanized steel sheet is immersed for 1 to 10 seconds in an aqueous solution of Zn.
O 2 oxide was generated.・ Electrolysis: Zn (NO ₃ ) ₂・ 6H ₂ O 400 g / l, HNO ₂ 70 g / l in aqueous solution, current density 7 A / dm ² , 1 to 7 with plated steel sheet as cathode
ZnO oxide was produced by second electrolysis.・ Steam: On the surface of galvanized steel sheet (500 ℃) after alloying treatment
80-125 l / min of atomized water was injected to produce ZnO oxide. The amount of ZnO oxide was measured by a chemical analysis method such as GDS (glow discharge spectroscopy) or IPC (ion plasma emission spectrometry). Note 3) Inorganic oxide generation method-Mn oxide is potassium permanganate or manganese carbonate-P oxide is phosphoric acid or sodium phosphate, potassium phosphate, ammonium phosphate-Mo oxide Are ammonium molybdate, Co oxides are cobalt carbonate and cobalt nitrate, Ni oxides are nickel nitrate and nickel carbonate, Ca oxides are calcium nitrate and calcium carbonate, W oxides. Is ammonium tungstate or sodium tungstate, V oxide is ammonium vanadate or sodium vanadate, and borate is sodium borate as the element concentration.
The mixture was mixed in the range of 0.1 to 50 g / l, dipped or sprayed, and the coating amount was adjusted by an air knife or a roll squeeze to form an oxide, which was dried. Further, in order to secure the solubility of the above elements, pH adjustment was performed with sulfuric acid, nitric acid, zinc carbonate, sodium hydroxide, potassium hydroxide as necessary. The amount produced is the measured elemental amount. The amount of oxide is GDS (glow discharge spectroscopy) or IPC (ion plasma emission spectrometry)
The chemical analysis method according to Note 4) Aging method Aging method A: After forming (coating) an inorganic oxide film, the aging liquid was sprayed in an atomized state without drying, and dried at a plate temperature of 60 ° C. Aging method B: After forming (coating) an inorganic oxide film, it was dried, roll-coated with an aging liquid, and dried at a plate temperature of 60 ° C. Aging method C: After forming (coating) an inorganic oxide film, it was dried and dissolved with a rust preventive oil (Knoxlast 530F40: manufactured by Parker Kosan Co., Ltd.) to apply oil. Note 5) Dissolution amount A degreasing solution (SD550 manufactured by Nippon Paint Co., Ltd.) was prepared according to the formulation, immersed at 50 ° C for 2 minutes, washed with water and dried to elute the inorganic oxide film formed on the zinc-plated steel sheet. The amount was measured by measuring the concentration in the solution or the coating amount of the treated steel sheet before and after the degreasing treatment, and indicated by the coating weight loss. Note 6) Pressability (friction coefficient) Sample size: 17 mm x 300 mm, pulling speed: 50
0 mm / min, square beat shoulder R: 1.0 / 3.0 mm, sliding length: 200 mm, oil: Knoxlast 530F40 (Parker Kosan Co., Ltd.) under a condition of 1 g / m ² with a surface pressure of 100.
A several-point test was conducted in the range of up to 600 Kgf, the pull-out load was measured, and the friction coefficient was determined from the surface pressure and the slope of the pull-out load. Note 7) Chemical conversion treatment SD5000 (manufactured by Nippon Paint Co., Ltd.) was used as the chemical conversion treatment liquid, and degreasing and surface preparation were performed as prescribed and post chemical conversion treatment was performed. The chemical conversion coating is judged by SEM (secondary electron image): ○ if the coating is uniformly formed, △ if it is partially coated, and × if it is not coated. It was determined. Note 8) Welding conditions 1) Pressurizing force: 250kgf 2) Bad initialization time: 40 cycles 3) Energizing time: 12 cycles 4) Holding time: 5 cycles 5) Welding current: 11KA 6) Tiffle tip diameter: 5.0φ ( Frustum of a truncated cone type) 7) Electrode life end point determination: the number of dots at which the nugget diameter at 85% of the welding current can cover 3.6 mm. 8) Electrode material: Cu-Cr (generally used). Welding was performed by stacking two sheets with one side of the plated steel sheet facing up and the other side facing down, and taking consecutive points.

[0025]

EFFECTS OF THE INVENTION According to the present invention, the elution of the inorganic oxide is ensured during the chemical conversion treatment such as the degreasing treatment of the galvanized steel sheet on which the inorganic oxide excellent in pressability and chemical conversion treatment is formed. And the pressability and chemical conversion treatability can be improved. In addition, it is possible to prevent the chemical conversion treatment liquid such as degreasing degreasing liquid from being contaminated and prevent the functional deterioration of the liquid, and to extend the life of the liquid and reduce the cost while maintaining high chemical conversion treatment ability. Excellent effect can be obtained.

Claims (3)

[Claims] 1. After forming an inorganic oxide on the surface of a zinc-based plated steel sheet, contacting it with an aqueous solution containing a aging accelerator,
A method for producing a zinc-based plated steel sheet excellent in pressability, chemical conversion treatment resistance, and degreasing liquid stain resistance, which is characterized by aging an inorganic oxide. 2. The pressability, chemical conversion treatment property, and degreasing liquid stain resistance according to claim 1, wherein ZnO-based oxides are formed on the surface of the zinc-based plated steel sheet, and inorganic oxides are formed in the upper layer. An excellent method for producing a zinc-plated steel sheet. 3. Mn, Mo, P, Co, C as an inorganic oxide
It produces one or more oxides of a, Ni, W, V, and B, and is characterized in pressability, chemical conversion treatability, and degreasing liquid stain resistance according to claim 1 or claim 2. An excellent method for producing a zinc-plated steel sheet.