JPH06136556A - Surface treated steel sheet excellent in workability and corrosion resistance - Google Patents

Abstract

PURPOSE:To provide a surface treated steel sheet excellent in workability and corrosion resistance by subjecting a steel sheet to a direct chromating treatment and a resin treatment. CONSTITUTION:The surface treated steel sheet excellent in workability and corrosion resistance is provided with a chromate layer as a primary layer having chromium coating weight of 20 to 200mg/m<2> expressed in terms of metallic chromium at least on one side of a steel sheet and an organic resin layer as a secondary layer having 0.3 to 6.0mum dry film thickness by an organic resin mixture contg. a powdery lubricant by 0.5 to 20 pts.wt. to 100 pts.wt. organic resin on its surface. In the powdery lubricant, wax and/or fluororesin having 0.3 to 50mum average grain size is used, and its average grain size is preferably regulated to 1.0 to 10 times of the dry film thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet which is mainly used for home appliances, office automation equipment, automobiles, etc., which are processed by press forming to improve the workability and corrosion resistance of the steel sheet and make it easier to use.

[0002]

2. Description of the Related Art Steel sheets are widely used in the fields of home electric appliances, office automation equipment, automobiles, building materials, etc., and are often subjected to various press workings in the manufacturing process of these products.

Lubricant oil is usually applied to the surface of the steel sheet during press working, but this work has the following problems. (1) Lubricant cannot prevent the occurrence of mold galling during press working. (2) Since the lubricating oil is often applied by spraying, the lubricating oil scatters around and the working environment deteriorates. (3) After press working, degreasing and
It needs to be washed, but in this process, the solvent (CFC,
1,1,1-trichloroethane etc.) is used.

Therefore, as an epoch-making product which can be press-formed without oiling and the degreasing step can be omitted, a chromate layer is formed on a galvanized steel sheet, and a resin layer containing various lubricants is further formed thereon. So-called lubricating steel sheets have been developed (for example, JP-A-60-103185 and JP-A-62-73938). However, these conventional techniques cannot meet the demands of customers for higher workability and lower prices.

[0005]

The drawback of the prior art as described above is that a galvanized layer is formed on the steel sheet to ensure corrosion resistance. That is, the zinc plating layer having a hardness lower than that of the steel sheet originally reduces the workability of the steel sheet, and it was desirable to omit it from the viewpoint of workability, but it is necessary from the viewpoint of corrosion resistance. It was

Further, in these prior arts, since a steel plate is plated, and then chromate treatment and resin coating treatment are performed, it is necessary to perform treatment for two or more lines in some cases, which causes a significant increase in manufacturing cost. There was a flaw.

Therefore, it is an object of the present invention to provide a surface-treated steel sheet which is excellent in workability and corrosion resistance and which solves the above-mentioned drawbacks of the prior art.

[0008]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted extensive studies to overcome these drawbacks of the prior art, and as a result,
The inventors have found that a steel sheet having the same degree of corrosion resistance as a plated steel sheet can be manufactured by directly subjecting the steel sheet to chromate treatment and resin treatment, resulting in the present invention.

That is, according to the present invention, 20 to 200 mg in terms of metallic chromium is formed as the first layer on at least one surface of the steel sheet.
A dry film thickness of an organic resin mixture having a chromate layer having a chromium deposition amount of / m ² and containing 0.5 to 20 parts by weight of a powdery lubricant as a second layer on 100 parts by weight of the organic resin. It is intended to provide a surface-treated steel sheet having excellent workability and corrosion resistance, which is characterized by having an organic resin layer of 0.3 to 6.0 μm. Here, the powdered lubricant is a wax and / or a fluororesin having an average particle size of 0.3 to 50 μm, and the average particle size thereof is 1.
It is preferably 0 to 10 times.

[0010]

The present invention will be described in more detail below. The steel sheet in the present invention is a cold-rolled steel sheet and a hot-rolled steel sheet having a plate thickness of 3 mm or less, which are objects of press forming, and are used in a state where mill scale does not exist on the steel sheet surface.

The chromate layer formed as the first layer on the surface of the steel sheet according to the present invention is intended for corrosion protection in indoor use or in a relatively mild corrosive environment that is not directly exposed to wind and rain, and has corrosion resistance and processability. From the viewpoint of, it is preferable to use a coating type chromate.

In the case where the steel sheet is directly subjected to chromate treatment, if the chromium deposition amount is less than 20 mg / m ² , the anticorrosion effect is not sufficient,
If it exceeds 200 mg / m ² , the anticorrosion effect is saturated and it becomes uneconomical. Also, when coating after processing, there is a risk that the chromate layer may be destroyed and peeling of the coating film may occur, so it is 20 to 200.
The range was limited to mg / m ² .

As the organic resin of the organic resin layer formed on the first layer, an epoxy resin, an alkyd resin, an acrylic resin, a urethane resin, a phenol resin, a melamine resin, a polyvinyl butyral resin, which have good adhesion to a steel plate, One or a mixture of two or more such as a polyester resin is preferable.

If the dry film thickness of these organic resin mixtures is too small, sufficient corrosion resistance and workability cannot be obtained, and if it is too large, a part of the film peels off during processing, causing a decrease in workability. It was limited to the range of 0.3 to 6.0 μm.
A more preferable range is 0.5 to 5.0 μm.

As the powdery lubricant to be mixed with the above-mentioned organic resin, it is preferable to use natural wax, synthetic wax, fluororesin or a mixture thereof. Examples of the natural wax include wooden wax, beeswax, palm wax and the like. As a synthetic wax,
Examples thereof include polyethylene wax, polypropylene wax, polybutene wax and the like. Examples of the fluorinated resin include polytetrafluoroethylene resin,
Examples thereof include polyvinyl fluoride resin and polyvinylidene fluoride resin.

These lubricants have an average particle size of 0.3 to 50.
It is preferably used in a range of 1.0 to 10 times the dry film thickness. If the average particle size of the lubricant is too small compared to the dry film thickness, the lubricity may be insufficient. Conversely, if it is too large, the lubricant may easily fall off during handling and sufficient workability may not be obtained. is there. A more preferable range is 1.5 to 5 times the dry film thickness.

The addition of less than 0.5 parts by weight of the powdery lubricant to 100 parts by weight of the organic resin is not sufficient for improving the lubricity, and the addition of more than 20 parts by weight causes the cohesive force of the organic resin to be increased. Since there is a risk of lowering the coating composition and a risk of lowering the coating adhesion of the post-coating, the content is limited to the range of 0.5 to 20 parts by weight.

In the present invention, from the viewpoint of only press formability, if only the surface of the die for press working which comes into contact with the die has the resin layer, the formability is secured without the resin layer on the punch side. However, it is desirable to have chromate layers on both sides from the viewpoint of ensuring corrosion resistance.

In the case of a single-sided resin-treated material, it is necessary to manage the punch side surface and die side surface so that they are not confused at the time of press working, and there is a drawback that the management of the material becomes complicated, but the surface without resin treatment becomes electrically conductive. Since there is also an excellent advantage, it is preferable to select double-sided treatment or single-sided treatment according to the purpose of use.

[0020]

EXAMPLES The present invention will be specifically described below based on examples. (Example) The following cold-rolled steel sheet was used as a test piece, and a plated steel sheet was used as a comparative material. However, the steel materials A to C are SP
It is a CC equivalent product. A: Cold-rolled steel sheet thickness 1 mm B: Electrogalvanized steel sheet thickness 1 mm, zinc coating adhesion amount 20 g / m ² C: Hot dip galvanized steel sheet thickness 1 mm, zinc plating adhesion amount 60 g / m ^{2 The} above steel sheets 1, 1 After steam degreasing with 1,1-trichloroethane, chromate coating was performed with a spin coater, followed by drying and baking. For the resin treatment, the resin liquids shown in Table 1 were applied with a bar coater and then dried and baked.

The amount of chromate attached was measured by fluorescent X-ray analysis, and the amount of resin attached was measured by a gravimetric method. The particle size of the wax was obtained by direct observation with a microscope.

The workability was evaluated by punch diameter 3 without applying oil.
The limit drawing ratio by the 3 mmφ cylindrical drawing test was evaluated as follows. ⊚: Excellent draw ratio LDR 2.36 or more ◯: Good LDR 2.30 or more and less than 2.36 Δ: Normal LDR 2.24 or more and less than 2.30 ×: Bad LDR less than 2.24

The corrosion resistance was evaluated by measuring 70 × from the prepared test piece.
A 150 mm test piece was cut out, the end face was sealed with tape, and then a salt spray test (5% NaCl, 35 ° C.) was performed to evaluate the rust generation time. However, the steel sheet was evaluated for red rust, and the plated steel sheet was evaluated for white rust. ×: within 8 hours △: 8 to 24 hours ○: over 24 hours

The following chromates, organic resins and lubricants were used in this example. Chromate Chromate A: Nippon Parkerizing 4513H Chromate B: Kansai Paint Cosmer 150

Organic resin Epoxy resin Epicoat 1 manufactured by Yuka Shell Epoxy Co., Ltd.
Acrylic resin Almatex 74 manufactured by Mitsui Toatsu Chemicals, Inc.
9-7 Urethane resin Mitsui Toatsu Chemical Co., Ltd. Orestar polyvinyl butyral resin Denki Kagaku Kogyo Denka butyral Also, epoxy + acrylic resin is 100 parts by weight of epoxy resin, acrylic resin is 50 parts by weight, epoxy + urethane resin is epoxy resin 100. 1 part by weight of urethane resin
00 parts by weight, acrylic + urethane resin is acrylic resin 1
The urethane resin was 100 parts by weight with respect to 00 parts by weight.

Lubricants Wax 1 San Nopco SN Wax 22-SF Wax 2 San Nopco SL630 Wax 3 Yasuhara Yushi Kogyo Arrow Wax 4 Commercial Wax Fluorine Resin Asahi Glass AD1

The resin and the lubricant are mixed in a ball mill,
Upon mixing, a small amount of surface modifier was used, and part of the wax was adjusted in particle size by a ball mill in advance. Both the chromate and the resin were dried at a temperature of 150 ° C. Table 1 shows the surface treatment conditions, workability, and corrosion resistance evaluation test results.

As is clear from Table 1, all of the steels of the present invention show excellent workability and corrosion resistance, but the comparative examples outside the scope of the present invention are inferior in workability and / or corrosion resistance. That is, Comparative Examples A-1, B-1, and C-1 are inferior in workability and corrosion resistance because they are not treated with chromate and resin. A-2 has insufficient corrosion resistance due to insufficient chromate adhesion. In A-3, since the resin is too thick, powdering of the resin occurs and the workability is not sufficient. A-4 is not enough in workability and corrosion resistance because the resin is too thin. A
In No. 5, the lubricant was too much, so that the corrosion resistance was impaired and the workability was slightly impaired. Since A-6 has too little lubricant, sufficient workability cannot be obtained. B-1, B-2, C-1, C-2
Since is subjected to galvanizing, the workability is inferior to that of the cold-rolled steel sheet as it is even if a predetermined surface treatment is performed.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

[Table 4]

[0033]

As described above, according to the present invention,
Sufficient workability and corrosion resistance can be obtained without plating on a steel sheet, and a surface-treated steel sheet that can be press-formed without oiling and degreasing steps can be provided at a lower price. As a result, the omission of the press molding process and the improvement of the environment are further promoted.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Katsuhei Kikuike, Katsuhei Kikuchi, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Technical Research Division (72) Yoshihiro Naruse, Hiroshi Chuo-ku, Chiba Kawasaki Town No. 1 Kawasaki Steel Corporation Technical Research Division

Claims (2)

[Claims] 1. A first layer formed on at least one surface of a steel sheet.
20 to 200 mg / m in terms of metallic chromium ² Of chromium
It has a chromate layer consisting of
0.5 to 20 parts by weight of powdered lubricant for 100 parts by weight of fat
Dry film thickness of 0.3 to 6.
Workability characterized by having an organic resin layer of 0 μm,
Surface-treated steel sheet with excellent corrosion resistance. 2. The powdered lubricant has an average particle size of 0.3 to
The surface-treated steel sheet having excellent workability and corrosion resistance according to claim 1, which is a wax and / or a fluororesin having a thickness of 50 μm and has an average particle diameter of 1.0 to 10 times the dry film thickness.