JPH04176878A - Galvanized steel sheet having excellent press formability and chemical conversion treataqbility - Google Patents

Abstract

PURPOSE:To produce the galvanized steel sheet having excellent press formability and chemical conversion treatability by forming films essentially consisting of oxides or hydroxides of specific metals and films essentially consisting of oxygen acids of P, B, etc., or oxide colloids of specific metals on the galvanized steel sheet. CONSTITUTION:The adhesion preventive function films which consist essentially of the oxides or hydroxides of >=1 kinds among Mn, Mo, Co, Ni, Ca, Cr, V, W, Ti, Al, and Zn and maintain the coatings in follow up to the deformation of the plating layers by tightly sticking to the surfaces of the plating layers at the time of press forming are formed in the amt. of 1 to 500mg/m<2> on the surfaces of the steel sheet plated with Zn or Zn alloy. Further, the films which consist essentially of the oxygen acids of one or two kinds of the P and B or the oxide colloids of >=1 kinds among Si, Al and Ti and have a rolling lubrication function are formed at 1 to 500mg/m<2> and total 2 to 1000mg/m<2> inorg. coating layers thereon.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a zinc-based plated steel sheet with excellent press formability and chemical conversion treatment properties.

[Conventional technology]

As a method for improving the press formability of zinc-based plated steel sheets, for example, as described in JP-A No. 62-185883, electrolytic chromate treatment is applied to the surface of the plated steel sheets, and Cr,
A method for producing an oxide film of O, and JP-A-62-
As described in Publication No. 192597, it is possible to form a hard film on a zinc-based plated steel sheet, such as by applying iron-zinc alloy plating, to prevent galling of the plating and die during pressing and to improve the lubricity of the press. Disclosed.

Further, as described in JP-A-1-136952, it is disclosed that the surface of a plated steel sheet is coated or coated with an organic substance such as an organic lubricating film or lubricating oil to improve press formability.

[Problem to be solved by the invention]

However, such products have the following disadvantages when used by automobile users.

The general usage process for automobile users consists of a process of cleaning steel sheets with oil, a pressing process, a degreasing process, a chemical conversion process, and a painting process. In the case of steel sheets that do not form a film or have been coated with lubricating oil or a lubricating film, sufficient lubrication performance will not be achieved as the oil will come off during the cleaning process, and furthermore, the degreasing process before chemical conversion treatment will be burdensome and costly. becomes higher. On the other hand, zinc-plated steel sheets subjected to iron-zinc alloy flash plating have problems such as higher cost of the steel sheets compared to electrolytic chromate treatment.

In view of the current situation, it is an object of the present invention to provide a zinc-based plated steel sheet that is low in cost, can be chemically treated, and has excellent press formability and chemical conversion treatment properties that can be manufactured without adding load to processes such as degreasing. With the goal.

[Means to solve the problem]

The gist of the present invention is as follows.

(1) An inorganic coating on the surface of the plating layer that has an anti-adhesion function that adheres to the surface of the plating 1 during press molding and maintains the coating by following its deformation, and a rolling lubrication function between the mold and the plating layer. Layer 2~1000mg/m2 (as metal)
A zinc-based plated steel sheet with excellent press formability and chemical conversion treatment properties.

(2) The zinc-based plated steel sheet having excellent press formability and chemical conversion treatment properties as described in the preceding item 1, which has a strong adhesion prevention function on the interface with the plating layer and a strong rolling lubrication function on the surface of the coating layer, which is coated with an inclined coating.

(3) The film with anti-adhesion function is made of Mn, Mo, C.
o, NiCa+ Cr, v, w, h, Aj+
One or more metal oxides of Zn and/or
Or, it is mainly composed of hydroxide, and the film amount is 1 to 500 ■/r.
rr (as a metal), and the film having a rolling lubrication function is mainly composed of one or two types of oxygen acids such as P and B and/or one or more types of oxide colloids of Sx + Aj + Ti, and the film amount is 1 Press formability according to the preceding clause 1 or 2, wherein ~500 / is (as metal);
Zinc-based plated steel sheet with excellent chemical conversion treatment properties.

The zinc-plated steel sheets to which the present invention is directed include those produced by various manufacturing methods such as hot-dip plating, electroplating, vapor deposition plating, and thermal spraying, and the plating composition includes not only pure Zn but also Zn and Fe, Zn and Ni.

Zn and Aj, Zn and Mn, Zn and Cr, Zn and Ti
, Zn and Mg with Zn as the main component, or with Fe, Ni + Co + to improve various functions such as corrosion resistance.
AI, Pb, Sn, Sbt Cu, Ti+S
Contains one or more alloying elements and impurity elements such as i, B, P, N, S, O, etc., and SiOtrkl
Ceramic fine particles such as tOs, TiO2, BaCr
There are those in which oxides such as 0° and organic polymers such as acrylic resin are dispersed in the plating layer, and there are those with a single composition in the thickness direction of the plating layer, and those whose composition changes continuously or layered. , and in multilayer plated steel sheets, the top layer is
In addition to pure Zn, the plating composition includes Zn and Fe, Zn and Ni, Zn and AZ, Zn and Mn, and Zn and Cr.

Mainly composed of Zn such as Zn and Ti+ Zn and Mg, containing one or more alloying elements and impurity elements to improve various functions such as corrosion resistance, and SiO□.

Ceramic fine particles such as Altos, TiO2, Ba
There are some in which oxides such as CrO4 and organic polymers such as acrylic resin are dispersed in the plating layer.

For example, hot-dip galvanized steel sheets, vapor-deposited galvanized steel sheets, iron-zinc alloyed hot-dip galvanized steel sheets, hot-dip galvanized steel sheets made of zinc-based alloys such as aluminum and iron, and the lower layer is alloyed in the cross-sectional direction of the plating layer. Alloyed hot-dip galvanized steel sheet (generally referred to as half-alloy), galvanized steel sheet consisting of an iron-zinc alloyed hot-dip galvanized layer on one side and a hot-dip galvanized layer on the other side, zinc coated on these plating layers by electroplating, vapor deposition plating, etc. or steel sheets plated with metals containing zinc as the main component and iron or nickel, electrogalvanized steel sheets, zinc, nickel, chromium alloy electroplated steel sheets, etc., single alloy layer or multilayer alloy electroplated steel sheets, There are steel sheets coated with zinc and zinc-containing metals. In addition, there are dispersion-plated steel sheets in which ceramic fine particles such as SiO2 and A1z03, TiO□ oxide fine particles, and organic polymers are dispersed in zinc or zinc alloy plating.

By coating the surface of such a zinc-based plated steel sheet with a plating metal adhesion inhibitor and a lubricant as described above, press formability and chemical conversion treatment properties are improved.

[Effect]

Since galvanized steel sheets generally have a soft plating layer, they easily undergo plastic deformation during press forming and fit into the surface roughness profile of the mold, increasing the actual contact area with the mold and increasing frictional force. As a result, the plating layer is torn off, and the peeled off plating pieces act as a binder, tear off the plating layer one after another, accumulate in the mold, and have a strong tendency to eventually cause material breakage.

Usually, anti-corrosion oil is applied to the surface of the galvanized steel sheet, and in some cases, press oil is applied to the surface of the sheet for pressing. The effect of the oil film is to form a fluidized layer between the mold and the plating surface, suppressing direct contact between the metal and reducing the above phenomenon, but the oil film is easily broken on the sliding surface with the mold. , not fully resolved.

Attempts have been made to increase the strength of the oil film by applying high-viscosity lubricating oils or hot-melt solid lubricating oils, and although these have some effect in reducing frictional force, they are not effective in the post-molding degreasing, chemical conversion treatment, and painting processes. Problems include poor degreasing, contamination of the degreasing solution, shortening the service life, failure to form a chemical conversion film, or deterioration of corrosion resistance.

The method of flash plating a hard metal, such as an Fe-based alloy, on the surface of a zinc-based plating works by coating the soft zinc-based plating to increase the hardness of the composite system and reduce the actual contact area with the mold. Therefore, in order to exhibit the effect, it is necessary to perform a thick surface layer plating of about 0.5 μm or more, which increases the cost.

The present invention forms a novel film on a galvanized steel sheet that operates through a mechanism completely different from that of the above-mentioned methods.

That is, a film having an anti-adhesion function mainly composed of metal oxides and/or hydroxides of 1 to 500 cm/i (as metal) on the zinc-based plating surface, and 1 to 500 m
g/m2 (as metal) of an oxyacid and/or metal oxide colloid to form a film having a rolling lubricating function. This film has an amorphous structure mainly composed of metal-oxygen bonds, and the film structure with anti-adhesion function and the film structure with rolling lubrication function coexist with each other through oxygen bonds. However, it is not something that can be separated as a layered structure.
It can be identified as a function during press molding.

During press working, the amorphous metal oxygen bonding structure follows the new surface of the deformed galvanized layer and adheres to the zinc via enzyme bonds, preventing zinc from adhering to the mold. On the other hand, part of the film is destroyed and becomes powder, which performs a rolling lubrication function on the sliding surface with the mold, which is the reason why it shows revolutionary lubricity despite being an extremely thin inorganic film. Conceivable.

- As an example, Mn8■/E on electrogalvanized steel sheet.

FIG. 1 shows an electron micrograph showing the formation of an amorphous oxide film consisting of P5■/BO. Only the galvanized crystals are visible, and the thin surface film is not visible at all. Line analysis with an electron probe microanalyzer results in the following (as shown in Figure 2).
The presence of Mn and P can be confirmed. Figure 3 shows the surface condition of this steel plate under an electron microscope after it was subjected to a drawbead sliding test, and the zinc-plated surface was rubbed by the mold bead, leaving no trace of the original zinc crystals. In an electrogalvanized steel sheet without treatment, the condition would cause the sheet to break, but when the film of the present invention is formed, the coefficient of friction is 0.17, and a good lubrication state is maintained. FIG. 4 shows an electron probe microanalyzer line analysis chart after the drawbead sliding test. Mn of the film.

Although the abundance of both P has decreased compared to before the sliding test,
There are no breaks in the film and it remains fairly uniform. Even if a new zinc surface appears due to sliding, it can be understood that the film is being reorganized. Here, when paying attention to the MnZP ratio, it can be seen that P is relatively reduced compared to before sliding. It is thought that P in the film was selectively destroyed and turned into powder, contributing to rolling lubrication.

Films with anti-adhesion function include Mn, ? IO,
-Co, Ni, Ca, Cr+'V, W, Ti
, Aj+ Zn, etc. The film mainly has an amorphous structure mainly composed of metal oxides and/or hydroxides, and has a rolling lubrication function. It is thought that a structure in which an oxide colloid consisting of the like is bonded to the amorphous structure via an oxygen bond mainly functions.

However, the film formation reaction occurs from the aqueous solution to the interface p.
Since it is deposited in a harmonious manner by utilizing the increase in H, it is not possible to strictly select the function, but it is better to understand that part of the film has an anti-adhesion function and the other part has a rolling lubrication function. It is reasonable.

All of the above-mentioned film constituent components are inorganic substances, do not put any load on the degreasing solution after pressing, and are dissolved by lowering the pH during chemical conversion treatment, so that a chemical conversion film can be formed normally.

The film can be formed reliably by immersing the zinc-plated steel sheet in an acidic aqueous solution containing a film component with an anti-adhesion function and a film component with a rolling lubrication function, or by cathodic electrolytic treatment. In the immersion treatment, when Zn dissolves, the pH at the interface increases, and as a result, film components precipitate as hydroxides or oxides. Melted Zn and other plating layer bones are also mixed into the film.

Redox reactions can also be used. The dissolution of Zn is an oxidation reaction, and correspondingly, oxidized metal ions precipitate as insoluble reduced oxides. Both oxyacid anions such as phosphoric acid and oxide colloids can be precipitated by increasing the pH at the interface. The cathodic electrolytic treatment has the effect of promoting an increase in pH at the interface. Attempts to control the interfacial reaction by adjusting the thickness of the water film, such as by spraying or coating, can also be applied to the present invention.

The appropriate amount of film having both adhesion prevention function and rolling lubrication function is 2 to 1000 .mu./rrf for metal.

If it is less than 2■/bo, no clear lubricating effect can be recognized, and 100
If it exceeds 0/I, there is a risk that the film will peel off in chunks, and the formation of the chemical conversion film may be adversely affected, which is not preferable. As an embodiment of forming a coating having both adhesion prevention function and rolling lubrication function, an amorphous structure film mainly composed of metal oxide and/or hydroxide and an oxyacid and/or metal oxide colloid film are formed. The coating amount is 1 to 500 μ/rr for both metals.
f is appropriate. If it is less than 111 g/rd, no clear lubricating effect can be perceived, and if it exceeds 500 g/n, there is a risk that the film will peel off in lumps, and the formation of the chemical conversion film may be adversely affected, which is not preferable.

An amorphous structure film mainly composed of gold WA oxide and/or hydroxide and an oxygen acid and/or metal oxide colloid film can be deposited by a chemical reaction at the interface such as the above-mentioned immersion method or cathodic electrolytic treatment method. is generally produced as a mixed film. However, it is also possible to form a film in a functionally graded manner, with the anti-adhesion function being stronger at the interface with the zinc plating and the rolling lubrication function being stronger at the surface of the film.

Although this method does not have a significant effect on the lubrication performance as indicated by the coefficient of friction, it does prevent galling when localized high pressure is applied to the galvanized steel sheet, such as when pressing difficult-to-form parts. This has the effect of improving the critical surface pressure that occurs. Since the so-called press forming load range can be widened, mold design becomes easier in practical use, and pressing work becomes stable, so great benefits can be enjoyed.

The method for producing a functionally graded film takes advantage of the differences in solubility products of metal oxides, etc., and adjusts the ion concentration of each component, flow rate, solution temperature, current density in the case of electrolytic treatment, etc. to improve the interface. It consists of controlling the ion concentration. For example, in the case of Mn and P-based coatings, potassium permanganate, phosphoric acid, and sulfuric acid are mixed in the treatment solution, and zinc plating fiI
When a reaction is caused with the plate, first, Mn oxide, which has the smallest solubility product, precipitates as Zn dissolves. At this time, the interfacial pH did not rise rapidly due to the presence of sulfuric acid, and then phosphoric acid M-
n or Zn precipitates with a delay. FIG. 5 shows a glow discharge spectroscopic analysis of the film thus formed in the thickness direction, and it can be seen that it is a functionally graded film in which P is enriched in the surface layer and Mn is enriched in the lower layer. This figure is a spectroscopic analysis diagram in the thickness direction of a functionally graded amorphous oxide film with a total of Mn8/rrf; P5/bo formed on an electrogalvanized steel sheet, with a film thickness of 7 nm, A sputtering time of about 0.4 seconds or more indicates a galvanized layer.

Next, as a method for producing the above-mentioned oxide film, for example, calcium nitrate, nickel nitrate, cobalt nitrate, and ammonium molybdate are each used at 50 to 800 g/l.
Add 5 to 60 g/l of phosphoric acid and add an etching aid (
The desired oxide film can be produced by immersing the zinc-based plated steel sheet in an aqueous solution consisting of sulfuric acid, etc., spraying the aqueous solution, or electrolytically treating the steel sheet in an aqueous solution using the steel sheet as a cathode.

(Example) Next, examples of the present invention will be listed together with comparative examples.

Note 1) Plated steel sheet AS: Alloyed hot-dip galvanized steel sheet (Fe: 10%.

At: 10.25%, residual Zn), EG: electrogalvanized steel sheet, G■: hot-dip galvanized steel sheet (At: 0.
3%.

Fe: 0.8%, Pb: 0.1%, remaining Zn), Zn
/Zn-Cr: Lower layer Cr1O% content 20g/n (zinc alloy plated steel sheet, upper layer Zn2g/n), Zn-Ni: Ni 12% residual Zn content electrical alloy plated steel sheet, Zn-Mn: Mn 40% residual Zn content electrical The alloy plated steel plate and the steel plate thickness are both 0.8 mm thick.

Note 2) Pressability (friction coefficient) Sample size: 17++wnX300mm, Tensile speed: 500mm/1IIin, Square beat shoulder R: 1
．． 0/3.0mm, sliding length: 200mm, oiling: Socklast 530F-40 (Parker Kosan Co., Ltd.) with an oiling amount of 1g/nf, and a surface pressure of 100 to 600kgf.
A several-point test was conducted between the two, the pull-out load was measured, and the coefficient of friction was determined from the slope of the surface pressure and pull-out load.

(Breaking limit load ratio) In the above-mentioned drawbead test, the surface pressure (presser load) at which the pullout load suddenly increases (I! is the fracture surface pressure) was determined from.

Note 3) The amount of anti-adhesion film and rolling lubrication film is expressed as the amount of metal. Note that the amount of metal melted and precipitated from the plating base is not shown because it cannot be measured.

Note 4) 5D5 is used for chemical conversion treatment liquid (zinc-phosphoric acid-fluorine treatment bath).
000 (manufactured by Nippon Paint Co., Ltd.), degreasing and surface conditioning were performed according to the prescription, followed by chemical conversion treatment.

Chemical conversion treatment films are judged by SEM (secondary electron beam image): ○ if the film is uniformly formed, △ if the film is partially formed, and △ if the film is not formed. It was judged as ×.

〔Effect of the invention〕

According to the present invention, it is possible to provide a zinc-based plated steel sheet whose slidability in press forming is improved to a level higher than that of a cold rolled steel sheet, which eliminates the stress during press forming, and which can also form a chemical conversion coating. The present invention is extremely useful industrially, as it is lower in cost and higher in quality than conventional methods, can reduce the burden on the user in the process, and can improve productivity during press molding.

[Brief explanation of the drawing]

Figure 1 is an electron micrograph showing the crystal structure of the amorphous oxide film formed on the surface of an electrogalvanized steel sheet, and Figure 2 is the surface on which the amorphous oxide film is formed on the surface of an electrogalvanized steel sheet. Electron probe microanalyzer line analysis diagram,
Figure 3 is an electron micrograph showing the crystal structure of the surface of the copper plate shown in Figure 1 after being subjected to a drawbead sliding test; Figure 4 is an electron probe microanalyzer line analysis diagram of the surface of the steel plate shown in Figure 3; FIG. 5 is an explanatory diagram of glow discharge spectroscopic analysis in the thickness direction of a functionally gradient amorphous oxide film formed on the surface of an electrogalvanized steel sheet. Figure 1 Figure 3

Claims (3)

[Claims] (1) An inorganic coating on the surface of the plating layer that has an anti-adhesion function that adheres to the surface of the plating layer during press molding and maintains the coating by following its deformation, and a rolling lubrication function between the mold and the plating layer. A zinc-based plated steel sheet with excellent press formability and chemical conversion treatment properties, characterized by forming a layer of 2 to 1000 mg/m^2 (as metal). (2) The zinc-based plated steel sheet with excellent press formability and chemical conversion treatment properties according to claim 1, wherein the anti-adhesion function is strong at the interface with the plating layer, and the rolling lubrication function is strong at the surface of the coating layer, and is coated with a slope. . (3) The film with anti-adhesion function is made of Mn, Mo, and Co.
, Ni, Ca, Cr, V, W, Ti, Al, and Zn, and the coating amount is 1 to 500 mg/m^2 (as metal). ), and the film having a rolling lubrication function is composed of one or two types of oxygen acids such as P and B and/or Si, Al, and T.
Mainly composed of one or more oxide colloids of i,
The zinc-based plated steel sheet with excellent press formability and chemical conversion treatment properties according to claim 1 or 2, wherein the coating amount is 1 to 500 mg/m^2 (as metal).