JPH03287785A - 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 and boric acid. 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 B and P) boric acid or boric acid and phosphoric acid.

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. ,Cr,03
A method for producing an oxide film of
As described in Publication No. 2597, 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.

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

The outline of the process used by automobile users consists of the process of cleaning steel sheets with oil, pressing process, degreasing process, chemical conversion treatment process, and painting process. If a treated film is not formed, or if the steel plate is 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. This increases the cost. −
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 galvanized steel sheet that can advantageously solve these demands.

(Problem to be solved by the invention) The gist of the present invention is as follows.

(1) Zn oxide 3-500 mg/rrT (
(as Zn), Mn oxide 5-500 wy;/rr
Zinc-based plated steel sheet with excellent press formability, chemical conversion treatment property, and weldability, which is obtained by coating the surface of the plated steel sheet with a film consisting of f (as Mn), boric acid less than 1000 μ/bo (as boron), and other oxides. .

(2) Zn oxide 3-500 mg/% (Zn
), Mn oxide 5 to 500mg/m2 (as Mn), phosphoric acid and boric acid less than 1000mg/m2 (as P, boron), and other oxides are coated on the surface of a plated steel sheet by press forming. Zinc-based galvanized steel sheet with excellent hardness, chemical conversion treatability, and weldability.

The zinc-based plated mesh sheets to which the present invention is directed include those made by various manufacturing methods such as hot-dip plating, electroplating, vapor deposition plating, and thermal spraying, and the plating composition includes pure Zn as well as Zn. and Fe, Zn and Ni.

Zn toni! , Zn and Mn, Zn and Cr, Zn and Ti
, Zn and Mg, with Zn as the main component, and Fe, Ni, Go, N, Pb to improve various functions such as corrosion resistance.
, Sn, Sb, Cu, Ti, St, B.

Contains one or more alloying elements and impurity elements such as P, N, S, O, etc., and also contains ceramic fine particles such as 5iQz, A7□0°, Tie, oxides such as BaCrO4, acrylic resin, etc. Some have organic polymers dispersed in the plating layer, some have a single composition in the thickness direction of the plating layer, some have a composition that changes continuously or in layers, and in multilayer plated steel sheets, the top layer has The plating composition includes pure Zn, Zn and Fe, Zn and Ni,
Zn and At, Zn and Mn, Zn and Cr, Zn and T
5i02. Ceramic fine particles such as jV203, Ti0z, BaCr0. There are some types in which oxides such as oxides, organic polymers such as acrylic resins 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 called half-alloy), plated m plate consisting of an iron-zinc alloyed hot-dip galvanized layer on one side and a hot-dip galvanized layer on the other side, and electroplating, vapor deposition plating, etc. on these plating layers. 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, steel sheets coated with zinc and zinc-containing metals, etc. In addition, there are dispersion-plated steel sheets in which ceramic fine particles such as SiO□, 7V, O, etc., TiO□ oxide fine particles, organic polymers, etc. are dispersed in zinc or zinc alloy plating.

On the surface of such a zinc-based plated steel sheet, as described above,
By coating with oxide, Mn oxide, boric acid, or boric acid and phosphoric acid, press formability, chemical conversion treatment properties, and weldability are improved.

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

In order to impart lubricity to a plated steel sheet during press forming, it is effective to form a hard film on the surface of a plated plate. 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 mixed 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 + B, P-based oxide film is not clear, it is mainly a network consisting of Mn-0, Zn-0, P-0, B-0 bonds, and is partially composed of 100, CO
.

It is assumed that it is an amorphous macromolecular structure in which groups are bonded together and metal supplied from plating is substituted.

In addition, since this film is an oxide film, it does not dissolve even in the cleaning process with oil or the degreasing process, resulting in a decrease in lubrication performance.
Does not put a burden on other processes.

In order to improve the adhesion and film formability 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, kl, 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.

As for the amount of this film, in order to improve press formability, it is sufficient to contain Mn oxide (as Mn) at least 5 cm/m2, but if the amount of Mn film exceeds 500 mg/m2, the chemical conversion coating will Formation becomes insufficient.

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

Next, in order to improve the adhesion, film formability, etc. of such a film, boric acid of 1000 μ/Ho (as boron) or less, or
Boric acid and phosphoric acid are mixed at 1000 μ/po (as boron, P) or less. It is recognized that this makes the structure of the Mn-based oxide film uniform, improves film formability, improves lubricity, and further improves press formability. However, if each exceeds 1000 .mu./m, chemical conversion treatment properties may deteriorate, which is not preferable. The lower limit only needs to exist.

In addition, the weldability is improved by the inclusion of Zn oxide, but the amount of Zn in the oxide film (per one side) is 3 to 500 mg.
/rrf. If it is less than 3 .mu./m1, there is no effect, and if it exceeds 500 .mu./m, the electrical resistance becomes large, the chip becomes susceptible to softening and deformation, and the life of the chip becomes short, which is not preferable. In other words, in welding, etc., the plating metal becomes molten due to heating and then progresses to alloying with the steel plate. However, when the plating metal comes into direct contact with the electrode tip while it is molten, the copper of the tip composition The zinc in the plating composition reacts selectively, forming a hard and brittle copper-zinc alloy layer that wears out the tip and shortens the life of the electrode tip.

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 furthermore, The plating metal 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 is deposited to protect the chip. The protective film becomes a metal film, and although the reason is not clear, the thickness, shape, etc. of the protective film do not change even if welding is continued, and good welding can be performed 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: Often about 40 to 80%, but generally a higher Fe concentration is preferable, especially when a high concentration Zn portion is locally present. In addition, the electrode protection metal includes the components of the plating metal, the components of the steel plate such as Mn and S,
It may contain electrode tip components such as and 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 boric acid do not adversely affect weldability as long as they are within the composition range of the present invention.

Thus, by simultaneously forming a film mainly composed of Mn and oxides of Zn, B, and P 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 10
0~800g/j! , boric acid 5-60g/I! , or potassium permanganate 1-70 g/l, zinc nitrate 100-8
00 g/l! ,,boric acid 5-60g/! , phosphoric acid 5~
The method employed is to immerse the plated steel plate in an aqueous solution containing 60 g/l, to electrolytically treat the plated steel plate in this aqueous solution using the plated mesh plate as a cathode, or to spray the aqueous solution onto the plated mesh plate.

Also, as an etching solution into such an aqueous solution, for example,
It is preferable to add 1 to 10 g/f of one or more of sulfuric acid, nitric acid, perchloric acid, phosphoric acid, etc. to improve the adhesion of the oxide film.

When an oxide film is formed on the surface of the plated steel sheet in this manner, a part of the plating layer and the alloy metal in the plating layer is 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%jj:Q, 25%, remaining Zn).

EG: electrogalvanized steel sheet, GI: hot dip galvanized steel sheet (A7: 0.3%, Fe: 0.8%, Pb: o,
1%, residual Zn), HA: semi-alloyed hot-dip galvanized steel sheet (
Fe: 5%, A7: Q, 3%, remaining Zn), ! if
All plates are made of ordinary steel with a thickness of 0.8 m.

Note 2) Press formability (friction coefficient) Sample size: 17+mX300wn, Tensile speed: 500 m+/sin, Square bead shoulder R: 1.0/
3, Omm, sliding length: 200mm, oiling: Nox last 530F40. Under the conditions of Ig/pi, the surface pressure is 100 to 60.
Several points were tested between 0 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 3) Chemical conversion treatment 5D5000 (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): ○ if the film is uniformly formed, Δ if the film is partially formed, and × if no film is formed. It was determined that

Note 4) Manufacturing conditions are potassium permanganate 1-10g/
l, zinc nitrate lOO~800g/j2, boric acid 5~60
Electrolytic treatment (5 to 10 A/da
+21.0 to 1.5 seconds) or immersion treatment to form an oxide film.

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

l) Pressure crab 250kgf 2) Initial pressurization time: 40Hr 3) Current application time: 12Hr 4) Holding time: 5Hr 5) Welding current: 11kA 6) Tip tip diameter: 5.0φ (cone-shaped) 7) Electrode life End point judgment: Nugget diameter at 85% of welding current is 3.
Number of dots that can secure 6 m 8) Electrode material: Cu-Cr
(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 consecutive welding points was determined.

Note 6) Measurement of oxides is by GDS (glow discharge spectroscopy)
, by 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 (2)

[Claims] (1) Zn oxide 3 to 500 mg/m^2 (as Zn), Mn oxide 5 to 500 mg/m^2 (as Mn)
A zinc-based plated steel sheet with excellent press formability, chemical conversion treatment property, and weldability, which is obtained by coating the surface of the plated steel sheet with a film consisting of boric acid of 1000 mg/m^2 or less (as boron) and other oxides. (2) Zn oxide 3 to 500 mg/m^2 (as Zn), Mn oxide 5 to 500 mg/m^2 (as Mn)
Zinc-based plating with excellent press formability, chemical conversion treatment properties, and weldability, which is made by coating the surface of a plated steel sheet with a film consisting of phosphoric acid and boric acid of 1000 mg/m^2 or less (as P, boron) and other oxides. steel plate.