JPS61213399A - Tin-free steel sheet for welded can and its production - Google Patents

Abstract

PURPOSE:To obtain a tin-free steel sheet for a welded can having superior corrosion resistance and weldability by successively forming a specified amount of metallic Cr layer and a specified amount of a nonmetallic Cr layer on the surface of a steel sheet and by projecting part of the metallic Cr. CONSTITUTION:The surface of a steel sheet is degreased, pickled and plated with Cr in an aqueous soln. contg. Cr<6+>. Electrolysis is then carried out in the same soln. using the steel sheet as an anode, and the steel sheet is treated as a cathode in an aqueous soln. contg. a Cr plating assistant and Cr<6+>. Thus, 40-150mg/m<2> metallic Cr layer and 5-25mg/m<2> nonmetallic Cr layer are successively formed on the surface of the steel sheet. Part of the metallic Cr has projections. The metallic Cr layer is not porous and covers the entire surface of the steel sheet, so the corrosion resistance before painting is improved. The projections improve the weldability.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is applicable to beverage cans, food cans, etc.
This relates to tin-free steel sheets for welded cans used in the field of miscellaneous cans such as 8-piece cans and bale cans.

<Prior art and its problems> Generally, tinplate and tin-free steel sheets are mainly used as materials for cans. Tin cans are rapidly transitioning from soldering irons to welding cans in order to save resources, reduce costs, and improve appearance, and the tin weight has also changed to 2.8 g/m2 or more.
．． Products with a weight less than 0 g/ideal weight have been developed.

However, from a cost perspective, even thin tinplates cannot be said to be superior to tin-free steel sheets, which is one of the reasons why the use of tin-free steel sheets is increasing.

Even tin-free steel sheets, which are advantageous in terms of cost, have serious problems. Tin-free steel sheet is a steel sheet with a thin film of metallic chromium and non-metallic chromium formed on its surface, and is mainly used for adhesives. This is to solve the disadvantages of tin-free steel sheets, which are not solderable and cannot be welded due to the high resistance and high melting point of the surface coating.

However, when the contents of the can are subjected to high-temperature sterilization, the adhesive portion may be torn and the can may be destroyed. Although considerable improvements have been made by modifying the chromium water-retaining oxide coating on tin-free steel sheets, bonded areas are always accompanied by such risks. If a tin-free steel plate that can be welded was developed, not only would this problem be eliminated, but the overlapping of the joints would be reduced from 5 to 0 (glued parts).
．． Since the number of layers is 2 to 0.4, the material can be saved, and there are also advantages such as the risk of vacuum leakage from the seaming part. Therefore, there are high expectations for the development of tin-free steel sheets that can be welded.

For example, Japanese Patent Publication No. 57-19752 and Japanese Patent Publication No. 57-36986 are already known as providing weldable tin-free steel plates and manufacturing methods. However, since all of these methods aim to improve weldability by reducing the amount of metallic chromium or non-metallic chromium, such tin-free steel sheets have a porous structure in the metallic chromium layer, which inevitably leads to Corrosion resistance will be significantly impaired.

<Objective of the Invention> The present invention aims to eliminate the drawbacks of the prior art described above, and provides a tin-free steel plate for welded cans with excellent corrosion resistance and an economical and stable manufacturing method thereof. .

<Structure of the Invention> The present invention has a metal chromium layer of 40 to 150 mg/m2 and a nonmetallic chromium layer of 5 to 25 g/m2 on the surface of a steel plate, and a part of the metal chromium is protruded. The present invention provides a tin-free steel plate for welded cans, which is characterized by:

The present invention also includes: 40-150mg/+w2 on the steel plate surface
When manufacturing a tin-free steel sheet, which has a metallic chromium layer of 5 to 25IIIg/■2 and a non-metallic chromium layer of 5 to 25IIIg/■2 on top of which a portion of the metallic chromium is protruding, an aqueous solution containing Cr6+ is used. The present invention provides a method for producing a tin-free steel plate for welded cans, which comprises electrolytically treating the steel plate as an anode after chromium plating, followed by cathodic treatment in an aqueous solution containing a chromium plating aid and Cr6+.

The present invention will be explained in more detail below.

The tin-free steel plate of the present invention has a surface of 40 to 150
It is a tin-free steel plate that has a metallic chromium layer of 1 g/++2 and a non-metallic chromium layer of 5 to 25 g/2, and a part of the metallic chromium is protruding, and has excellent corrosion resistance and weldability. Both are excellent steel sheets for cans.

The reason why the amount of metallic chromium was limited to a range of 40 to 150 mg/layer 2 is as follows. The amount of metallic chromium is 40mg/m
If the amount is less than 2, the metal chromium layer will have a porous structure and will not be able to sufficiently cover the steel plate surface, leading to a decrease in paint corrosion resistance (the evaluation method will be described later) (Figure 1). Even if the value exceeds the above, not only no further improvement in paint corrosion resistance can be expected, but also a decrease in weldability (
Therefore, in the present invention, the amount of metallic chromium is limited to a range of 40 to 150 mg/m2.

In addition, the metal chromium layer is smoother than the smooth one (Fig. 6a).
One in which a part of the metal chromium layer has a protruding shape (No. 6)
Figure b) has better weldability (the evaluation method will be described later) (Figure 2).

The biggest influence on resistance welding is the contact resistance, and the smaller the contact resistance, the better the weldability, and the contact resistance is reduced by increasing the pressing force through the Cu wire electrode. FIG. 3 shows the results of examining the contact resistance of a tin-free steel plate having a smooth metal chromium layer and a tin-free steel plate having a partially protruded metal chromium layer by varying the load. In both cases, the contact resistance decreases as the load increases, but the degree of contact resistance is greater when a part of the metal chromium is in a protruding shape.This is because when a load is applied, the protrusion of the hard metal chromium This is thought to be due to the fact that electricity can easily pass through the non-conductive, soft, non-metallic chromium layer.

Next, calculate the amount of non-metallic chromium from 5 to 25 in terms of metallic chromium.
The reason for limiting the range to tag7m2 will be explained. If the amount of nonmetallic chromium is less than 5 mg/2, a bolus structure will occur and the surface cannot be sufficiently coated, resulting in a decrease in paint corrosion resistance (Figure 4). When 25 tagI exceeds 2, the weldability decreases rapidly (Fig. 5). This is because if the non-metallic chromium layer becomes too thick, the protruding metallic chromium parts will overlap with the thick non-conductive non-metallic chromium. This is thought to be because the layer cannot be penetrated.

As mentioned above, 40 to 150 mg/m2 on the surface of the steel plate.
The tin-free steel sheet, which has a metallic chromium layer of 5 to 25 mgl and a non-metallic chromium layer of 5 to 25 mgl2, and in which a portion of the metallic chromium is protruded, is a steel sheet for cans that has excellent corrosion resistance and weldability.

Next, a method for stably and economically manufacturing such a tin-free steel plate for welded cans will be described.

The phenomenon of precipitation of granular or angular metallic chromium may be observed when chromium plating is performed intermittently. This is because microscopic non-uniform dissolution of the non-metallic chromium layer on the metallic chromium layer occurs when electrolysis is interrupted, and this causes abnormal precipitation of metallic chromium when electrolysis is restarted. However, with this method that relies on microscopic heterogeneous dissolution of the nonmetallic chromium layer, it is difficult to stably obtain protruding metallic chromium, and the protruding metallic chromium is precipitated in the width direction of the steel sheet. It is unsuitable for industrial use such as batch production.

Therefore, the inventors researched a method for stably and industrially dissolving non-metallic chromium at a microscopic level, and found that
We discovered that anodization (reverse electrolysis) is superior.
This can be applied to both one-component and two-component methods, but it requires cathodic treatment in which metallic chromium is deposited after anodizing, and metallic chromium and non-metallic chromium layers are present before anodizing. That is essential.

Methods for precipitating metallic chromium after anodizing include sulfuric acid radicals, fluorides (Na2 SiF 6, NaBF4
Cathodic electrolysis in an aqueous solution containing Cr&+ and a chromium plating aid such as , NaF, etc.) is sufficient. Metallic chromium does not precipitate by cathodic electrolysis in an aqueous solution containing Cr&+ without such a chromium plating aid. The above-mentioned Cr6+ An aqueous solution containing at least one of chromic acid, dichromic acid, and salts thereof as a main component.

<Examples> Next, the present invention will be specifically explained with reference to Examples and Comparative Examples.

Example 1 After normal degreasing and pickling on a cold rolled steel plate of O82■ thickness 1
The main process has started.

(: r03 150 gel, Na2 SiF 6 6
gel, ) + 2 SO40, 8 gel, 5 OA/dm2 Cr0360 g/41, O2
SO40.3gel, 15 A/d in aqueous solution at 40°C
A tin-free steel plate was obtained by cathodic treatment of m2×O for 8 seconds. The amount of metallic chromium was 105 mg/m2 and the amount of non-metallic chromium was 18 g/m2, and numerous protruding metallic chromium particles were observed.

Example 2 A cold-rolled steel plate with a thickness of 0.22 mm was subjected to normal degreasing and pickling, and then subjected to the main treatment.

Cr0380g/l, H2SO40.8g/view, 45℃
In an aqueous solution of 40 A/da2
A test material was prepared by cathodic treatment at 0 A/dm2×O for 3 seconds in the same bath.

The obtained tin-free steel sheet has a metallic chromium content of 52 mg.
/m2. The amount of nonmetallic chromium was 8 mg/m2, and there were countless protruding metallic chromium.

Example 3 A cold-rolled steel plate with a thickness of 0.2 mm was subjected to normal degreasing and pickling, and then subjected to the main treatment.

Cr03250g/l, H2SO42,5g/41
．． After cathodic treatment at 50A/dm2XQ for 7 seconds in an aqueous solution at 50°C, anodization at 15A/d layer 2X for 0.1 seconds, and cathodic treatment at 50A/dm2X O for 7 seconds again, CrO360gel, Na25iF a2
．． 8g/l, 20A/dm2 in aqueous solution at 45°C
Xo, cathode treatment was performed for 5 seconds to prepare a test material.

The obtained tin-free steel sheet has a metallic chromium content of 141 layers
/ Maro 2. The amount of nonmetallic chromium was 20 tag/2, and there were countless protruding metallic chromium.

Comparative Example 1 The same treatment as in Example 1 was performed except that anodization was not performed. The obtained tin-free steel sheet has a metallic chromium content of 1
With a layer of 10 g/2 and an amount of nonmetallic chromium of 16 mg/layer 2, no protruding metallic chromium was observed.

Comparative Example 2 The steps up to the anodic treatment were the same as in Example 1, but the final cathodic treatment was carried out in an aqueous solution of 360 g/l of CrO, 40″a, for 15
Cathode treatment was carried out at A/dm2×O for 8 seconds.

The obtained tin-free steel sheet has a metallic chromium content of 101008
7 layers 2, nonmetallic chromium amount 18 mg/layer 2, and no protruding metallic chromium was observed.

Comparative Example 3 A 0.2 mm thick cold rolled steel plate was subjected to normal degreasing and pickling, and then subjected to water treatment. Cr0350 gel, Na2S
iF6 2.4g/JL, Na2Cr2072
0g/l.

4 OA/dm2 x 0.2 seconds + in aqueous solution at 50°C
Intermittent electrolysis was performed at 15 A/dm2×O for 3 seconds to prepare a test material. The obtained tin-free steel sheet had a metallic chromium content of 15 mg/m2 and a non-metallic chromium content of 17 mg/m2.
, and no protruding metallic chromium was observed.

The tin-free steel sheets thus obtained were evaluated for coating corrosion resistance and weldability by the methods described below.

Table 1 summarizes the results.

Examples 1 to 3, which satisfied all the requirements of the present invention, were tin-free steel plates with excellent post-painting corrosion resistance and weldability. On the other hand, in Comparative Example 1, no anodization was performed, so there was no protruding metallic chromium, and the weldability was poor. In Comparative Example 2, the cathodic treatment after the anodic treatment was performed in an aqueous solution containing no auxiliary agent, so that no protruding metallic chromium was obtained, resulting in poor weldability.

Comparative example 3 has a small amount of metallic chromium at 15+*g/meal 2,
Although it showed acceptable weldability, the corrosion resistance after painting was significantly inferior.

The evaluation method for coating corrosion resistance and weldability is as follows.

(Evaluation of paint corrosion resistance) Apply epoxy phenol paint to tin-free steel plate.
11g/da 2 After painting and baking, the sample was immersed in tomato juice containing only lOO at 95°C in a 150mJ1 beaker, leaving the top part of the sample sealed, and the whole was sealed and heated at 55°C.
Hold for 8 days, depending on the degree of corrosion under the coating on the liquid surface, O ~ 5
The evaluation was divided into six stages.

(Evaluation of weldability) After dry firing the tin-free steel plate at 210°C for 20 minutes, electric resistance welding was performed at a welding speed of 40 m/min and a pressure of 40 Kgf to ensure that the welded part had sufficient strength and was over l-g The conditions under which the number of splashes was the smallest were found for each sample material, and the weldability was evaluated based on the number of splashes at that time.

4 1-23
3-52
6～101 11～
200 Above 21 Table 1 <Effects of the Invention> The tin-free steel sheet for welded cans of the present invention has good coating corrosion resistance because the metal chromium layer is not porous as in the past, but covers the entire surface of the steel sheet. Weldability is also good because some parts are protruding.

According to the method of the present invention, since unnecessary anions in the metal chromium layer can be removed by reverse electrolysis (anodization) of the metal chromium layer, paint corrosion resistance can be improved.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a graph showing the relationship between the amount of metallic chromium and paint corrosion resistance. FIG. 2 is a graph showing the relationship between the amount of metallic chromium and weldability. FIG. 3 is a graph showing the relationship between load and contact resistance when the metal chromium layer is smooth and when it has protrusions. FIG. 4 is a graph showing the relationship between the amount of nonmetallic chromium and paint corrosion resistance. FIG. 5 is a graph showing the relationship between the amount of nonmetallic chromium and weldability. FIGS. 6a and 6b are photographs substituted for drawings showing the metal structure, and are 8000x electron micrographs of a metal chromium layer having a smooth shape and a protruding shape, respectively. Patent Applicant: Kawasaki Steel Co., Ltd. Agent, Patent Attorney: Nozomi Watanabe;・-1 Patent Attorney: Yo Ishii.・7″・′;・ko’ku FIG, 1 Gold 1 chromium amount (mg7m2) FIG, 2 Metal chromium amount (mg/m”) FIG, 3 Look! FIo, 4 Non-metallic chromium content (m9/m2) FIG, 5 Non-metallic chromium content (mg/m2) FIG, 6a Temitane Hosho 4F (Voluntary) February 28, 1985 1 Display of incident 1985 Patent Application 'fJ52935 2, Title of invention: Tin-free steel plate for welded cans and its manufacturing method 3, Name of person making the amendment (125) Kawasaki Steel Corporation Drawing 6゜ Contents of amendment Drawing Figure 3 attached as attachment Replace as shown.・37.3-, F. 111~ - Appetizer! (Ri-O) Procedure Neho (spontaneous) June 13, 1985 Patent Application No. 52935 of 1985 2, Title of invention Tin-free steel plate for welded cans and manufacturing method thereof 3, Name of person making the amendment Name (125) Kawasaki Steel Corporation 4, Agent
101 Phone: 864-4498 Address: 3-2-2-6 Iwamoto-cho, Chiyoda-ku, Tokyo Contents of amendment (1) The following sentence is added after the third line of page 9 of the specification. Although it is possible to use a normal PB-based electrode as an anodizing electrode, as reported in Japanese Patent Application No. 59-074407, the surface can be coated with gold, platinum, or platinum black, which is less likely to cause the precipitation of metallic chromium. Using a coated electrode allows for more stable anodic treatment.

Claims (2)

[Claims] (1) Having a metal chromium layer of 40 to 150 mg/m^2 and a non-metallic chromium layer of 5 to 25 mg/m^2 on the steel plate surface,
A tin-free steel plate for welding cans, characterized in that a part of the metal chromium is protruding. (2) It has a metal chromium layer of 40 to 150 mg/m^2 on the surface of the steel plate and a non-metallic chromium layer of 5 to 25 mg/m^2 on top of it, with some of the metal chromium protruding. When manufacturing tin-free steel sheets, the steel sheet is electrolytically treated after being chromium plated in an aqueous solution containing Cr^6^+, using the steel plate as an anode, and then cathodically treated in an aqueous solution containing a chromium plating aid and Cr^6^+. A method for manufacturing a tin-free steel plate for welded cans, characterized by: