JPH03287784A - Zinc plated steel sheet having superior press formability, chemical convertibility and weldability - Google Patents

Abstract

PURPOSE:To improve the press formability, chemical convertibility and weldability of a Zn plated steel sheet by coating the surface of the steel sheet with a coating film consisting essentially of prescribed amts. of Zn oxide, Mn oxide, phosphoric acid, Mo oxide, W oxide and V oxide. CONSTITUTION:This Zn plated steel sheet is formed by coating the surface of a Zn plated steel sheet with a coating film consisting essentially of 3-500mg/m<2> (expressed in terms of Zn) Zn oxide, 5-500mg/m<2> (expressed in terms of Mn) Mn oxide and <=1,000mg/m<2> (expressed in terms of P, Mo, W and V) phosphoric acid, Mo oxide, W oxide and V oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a galvanized steel sheet having excellent press formability, chemical conversion treatment properties, and weldability.

(Prior art and problems to be solved by the invention) As a method for improving the press formability of a galvanized steel sheet, for example, as described in JP-A-62-185883, electrolytic chromate treatment is applied to the surface of the galvanized steel sheet. , Crx(h
A method for producing an oxide film of
As described in Publication No. 259'7, a hard film is formed 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 improve the lubricity of the press. This is 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.

However, such products have the following inadequacies when used by automobile users and the like.

The outline of the usage process for automobile users consists of the process of cleaning the steel plate with oil, pressing process, degreasing process, chemical conversion process, and painting process.In the case of electrolytic chromate treated steel plate, the chemical conversion coating is applied during the chemical conversion process. In the case of steel sheets coated with lubricating oil or a lubricating film, sufficient lubrication performance will not be achieved as the oil will fall 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, iron-zinc alloy flash plating applied to zinc-based plated steel sheets has the problem that the cost of the steel sheet is higher than that of electrolytic chromate treatment. There is a desire for the development of a galvanized steel sheet that does not place a burden on the process and has excellent press formability.

Furthermore, no particular measures have been taken in the past to improve weldability, and there is a strong demand for improvement in weldability in conjunction with press formability and chemical conversion treatment properties.

The present invention aims to provide a zinc-based plated mesh plate that can advantageously solve these demands.

(Problems to be Solved by the Invention) The gist of the present invention is that Zn oxide 3 to 500
mg/rrT (as Zn), Mn oxide 5-5
00■/bo (as Mn), phosphoric acid and Mo oxide, W oxide, one or more types of oxides below 1000■/bo (as P, Mo, W, V) and other oxides A galvanized steel sheet with excellent press formability, chemical conversion treatment properties, and weldability, which is coated with a film consisting of:

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, and Fe, Ni, Co, AI, P to improve various functions such as corrosion resistance.
b, Sn, Sb, Co, Ti, Si, B
.

Contains one or more alloying elements and impurity elements such as P, N, S, and O, and also contains S 10 z + N z
Ceramic fine particles such as 03, Tie, BaC
There are those in which oxides such as rO4 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. Furthermore, in multilayer plated steel sheets, the top layer contains pure Zn, Zn and Fe, and Zn.
and Ni, Zn and jV, Zn and Mn, Zn and Cr,
Mainly composed of Zn such as Zn, Ti + Zn and Mg, contains one or more alloying elements and impurity elements to improve various functions such as corrosion resistance, and also contains 5iOz, Nz
Ceramic fine particles such as 03, TiO□, BaCr
There are some in which oxides such as O4 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 mesh sheets, hot-dip galvanized steel sheets made of alloys such as aluminum and iron, whose lower layer is alloyed in the cross-sectional direction of the plating layer. Alloyed hot-dip galvanized steel sheet (generally called half-alloy), coated 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, and galvanized steel sheets that have an iron-zinc alloyed hot-dip galvanized layer on one side and a hot-dip galvanized layer on the other side. Steel sheets plated with zinc or metals containing zinc as the main component and iron or nickel, electrogalvanized steel sheets, zinc, nickel, chromium alloy electroplated steel sheets, etc., and single alloy layer or multilayer alloy electroplating. There are steel sheets, zinc, and vapor-deposited steel sheets containing zinc. In addition, there are dispersion-plated steel sheets in which ceramic fine particles such as 5iOz and A7z(h), TiO□ oxide fine particles, organic polymers, etc. are dispersed in zinc or zinc alloy plating.

As mentioned above, Zn is applied to the surface of such a zinc-based plated steel sheet.
oxide, Mn oxide, phosphoric acid and Mo oxide, W oxide,
(2) It attempts to improve press formability, chemical conversion treatment properties, and weldability by coating with a film composed of one or more oxides and other oxides.

(Function) The reason why the film has such an effect is as follows.

An effective method for imparting lubricity to a plated steel sheet during press forming is to form a hard film on the surface of the plated steel sheet. Electrolytic chromate treatment and iron-zinc alloy plating are effective in this regard, but the former cannot form a chemical conversion film;
The latter requires a large amount of processing and is expensive.

To solve these problems, the hard coating on the surface of the galvanized steel sheet must be an oxide coating, which can be dissolved in the chemical conversion treatment solution to form a chemical conversion coating, and at the same time, the coating components can be dissolved into the chemical conversion treatment solution. It is also necessary that the chemical conversion treatment is not adversely affected.

From this point of view, the present inventors have discovered that it is sufficient to form a Mn oxide film on the surface of a zinc-based plated steel sheet. Like the chromate film, the Mn oxide film becomes a glass-like film, suppresses galling of the plating on the die during pressing, and improves sliding properties.

Furthermore, since it dissolves in the chemical conversion treatment solution, it is possible to form a chemical conversion treatment film, unlike a chromate film, and there is no adverse effect even if it is eluted into the chemical conversion treatment solution.

When Zn oxide is used alone, it is difficult to form a film for improving press sliding properties by a wet method, but when used in a mixed crystal state with Mn oxide, press sliding properties can be significantly improved. Further, Zn oxide can also form a chemical conversion film, and there is no adverse effect even if it is eluted into the chemical conversion treatment solution.

Although the structure of the Mn, Zn, and P-based oxide film is not clear, it is mainly a network consisting of Mn-0, Zn-0, and P-0 bonds, and is partially bonded with -OH, CO3, Pot groups, etc. However, it is presumed that it is an amorphous macromolecular structure substituted by metal supplied from plating.

Furthermore, since this film is an oxide film, it does not dissolve even in the cleaning process with oil or the degreasing process, so the lubricating performance does not deteriorate and there is no burden placed on other processes.

In order to improve the adhesion and film formation properties of this film,
It is effective to add inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid, and salts thereof.

Furthermore, this film may contain substances contained in the treatment bath or plating as impurities.

These impurities include Zn, jV, Cr, Co,
Mn, Pb.

Sn, Cu, Ti, Si, B, N,
S, P, Cj, K, Na.

Mg, Ca, Ba, In, C, Fe, V
, W, Ni, etc.

Next, the coating amount range of the coating of the present invention will be described.

The amount of this film should be 51 g/n (or more) of Mn oxide (as Mn) to improve press formability, but if the amount of Mn film exceeds 500 g/n, the chemical conversion coating formation becomes insufficient.

Therefore, the appropriate amount of Mn oxide film is 5 /
It is more than 500 cm/po or less.

Next, in order to improve the adhesion, film formability, etc. of this film, phosphoric acid and Mo oxide, W oxide, IWi or 2
1000 mg/r4 or less (P, Mo.

By doing so, the structure of the Mn oxide film becomes uniform, film formability is improved, lubricity is improved, and press formability is further improved. Is recognized. However, if it exceeds 1000 .mu./ml, the chemical conversion properties may be deteriorated, which is not preferable, and it is sufficient that there is a lower limit.

In addition, the weldability is improved by the presence of Zn oxide, but the amount of such an oxide film produced is 3 to 500 m1 as the amount of Zn in the oxide film (per one side).
g/if. If it is less than 3■/Po, there is no effect, and if it exceeds 500■/I, the electrical resistance becomes large.
This is undesirable because the chip becomes soft and deformed, which shortens the life of the chip. In other words, in welding, etc., the plating metal becomes molten due to the heating, and then it progresses to alloying with the copper plate. When the plated metal comes into direct contact with the electrode tip while in a molten state, the copper in the tip composition and the zinc in the plating composition react selectively, forming a hard and brittle copper-zinc alloy layer, causing the tip to wear out and damage the electrode tip. It will shorten your lifespan.

This molten plated metal is cut off from contact with the chip by the oxide film formed on the surface of the plated steel plate, preventing melting damage caused by direct contact of the plated metal with the chip, and further, The plating metal in the molten state is alloyed with the iron of the steel plate, mainly forming an iron-zinc alloy, which adheres to the tip of the electrode tip through cracks in the oxide film or together with the oxide film, and accumulates to form the chip. Although the reason is not clear, the thickness, shape, etc. of the protective film do not change even if welding continues, and good welding can be achieved at all times, and damage to the chip can be prevented. Here, the electrode protection metal is mainly an alloy of plating metal and base iron, and has an average concentration of Fe: 20 to 60%.
, Zn: 40 to 80% in many cases, but generally Fe
A higher concentration is preferable, and it is particularly undesirable when a high concentration Zn portion is locally present. Further, the electrode protection metal may include components of the plating metal, components of the steel plate such as Mn and S, and components of the electrode tip such as Cu.

In addition, this electrode protective metal film has the effect of keeping the tip tip shape convex, so even if the tip is softened and damaged to the same extent, welding can be performed with a low current, and the tip protective film can be applied to only 50% of the tip surface. If it is attached to the above area, the life of the electrode tip can be significantly extended. That is, an oxide film mainly composed of ZnO is generated on the galvanized surface to which the electrode protection metal is attached, and an alloy of the plating metal and the steel sheet is passed through the oxide film using welding heat, or
The electrode protective metal is attached to the electrode tip together with the oxide film and welded.

Even if the Mn oxide is combined with the Zn oxide to form a film, the effect of improving weldability is observed as in the case of the Zn oxide described above. It is presumed that this is because the electrical resistance of the Mn-Zn composite oxide does not become so large.

Phosphoric acid and Mo, W, V oxides, etc. do not affect weldability as long as they are within the composition range of the present invention.

Thus, oxides of Mn and Zn and phosphoric acid, Mo.

By simultaneously forming a film mainly composed of W, oxide, etc. on a zinc-based plated steel sheet, both press formability and weldability can be improved, and chemical conversion treatment is also possible.

As a method for producing such an oxide film, for example, potassium permanganate may be used at 1 to 70 g/i! , zinc nitrate 100
~800g/A, phosphoric acid 1-60g/! , Mo acid and its salts, W acid and its salts, and (2) acid and its salts are selected and used, but 1 to 60 g/l is sufficient. In addition, it is effective to add one or more etching agents such as sulfuric acid, nitric acid, and perchloric acid.

The desired oxide film can be reliably produced by immersing the plated steel plate in such an aqueous solution, spraying the aqueous solution, or electrolytically treating the plated steel plate in the aqueous solution using the plated steel plate as a cathode.

When the oxide film is formed in this manner, the plating layer and a part of the alloy metal in the plating layer are mixed into the oxide film as other oxides.

(Example) Next, Examples of the present invention are shown in Table 1 along with comparative examples.

Note 1) Type of plated steel sheet: AS: Alloyed hot-dip galvanized steel sheet (Fe: 10%, jV: 0.25%, remaining Zn)
.

EG: Electrogalvanized steel sheet, GI: Hot-dip galvanized A sheet (Aj: 0.3%, Fe: 0.8%, Pb:
o, 1%, residual Zn), HA: semi-alloyed hot-dip galvanized steel sheet (Fe: 5%, Af: Q, 3%, residual Zn)
, tlijl plate thickness is 0.8 wm common steel.

Note 2) Press formability (friction coefficient) Sample size: 17m+X 300wm, Tensile speed: 500 mm/min, Square bead shoulder R: 1.0
/3.0mm, sliding length: 200mm, oiling: Nox Last 530F40. Under the conditions of Ig/po, the surface pressure is 100~
Tests were conducted at several points between 600 kgfO, the bow drawing load was measured, and the friction coefficient was determined from the surface pressure and the slope of the drawing load.

Note 3) Chemical conversion treatment 505000 (manufactured by Nippon Paint Co., Ltd.) was used as the chemical conversion treatment liquid, and the chemical conversion treatment was performed after degreasing and surface conditioning according to the prescription. Chemical conversion treatment films are judged by SEM (secondary electron beam image). Those with a uniform film formed are marked with O2. Those with a partially formed film are marked as Δ, and those with no film formed are marked with an x. I judged it.

Note 4) Manufacturing conditions are 1 to 70 g of potassium permanganate.
#, zinc nitrate 100-800g/f, phosphoric acid 1-60g
1 to 6 /l and one or more of Mo acid, W acid, ■ acid
0 g/l, electrolytic treatment (5 to IO
A/dm”.

1.0 to 1.5 seconds) to form an oxide film.

Note 5) Welding conditions The welding conditions are as follows.

1) Pressure crab 250kgf 2) Initial pressure application time: 40Hr 3) Current application time: 12) 1r 4) Holding time: 5Hr 5) Welding current 11kA 6) Tip tip diameter: 5.0φ (cone-shaped) 7) Electrode Life end point determination: Nugget diameter at 85% of welding current is 3.
Number of dots that can ensure 6 wn 8) Electrode material: Cu-C
r (Generally used) For welding, two plated steel plates were placed one on top of the other with one side facing up and the other side facing down, and the number of continuous welding points was determined.

Note 6) Measurement of oxides was performed by GDS (Glow Discharge Spectroscopy Corporation ICAP (ion plasma emission spectrometry)).

(Effects of the Invention) According to the present invention, in press forming, it is possible to improve the sliding properties to a level higher than that of cold-rolled steel sheets, to form a chemical conversion coating, and to improve weldability. can. As a result, it is possible to achieve excellent effects such as being able to reduce the cost and reduce the burden on the user in the process and improve productivity compared to the conventional method.

Claims (1)

[Claims] Zn oxide 3 to 500 mg/m^2 (as Zn),
Mn oxide 5 to 500 mg/m^2 (as Mn), phosphoric acid and one or more of Mo oxide, W oxide, and V oxide to 1000 mg/m^2 or less (P, Mo, W, A zinc-based plated steel sheet having excellent press formability, chemical conversion treatment properties, and weldability, the surface of which is coated with a film made of V) and other oxides.