JPH02298277A - Production of surface-treated steel sheet - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for preparing surface-treated steel sheets for welded cans that have excellent weldability and paint adhesion and are suitable for filling and preserving various foods, beverages, and other items. It is something.

Conventional technologyAs a material for containers used for foods, drinks, etc.1
Generally, there are tin plate and tin-free steel plate, and recently,
1 Tin-plated steel plate with reduced tin plating (F#! is also plated with Ni to ensure weldability),
Nickel-plated steel sheets and the like are also used for the purpose of reducing material costs. Simply looking at the cost, tin-free steel sheets are very superior to tin-plated steel sheets, tin-plated steel sheets, and nickel-plated steel sheets. In addition, tin-free steel sheets have excellent paint adhesion and post-painting corrosion resistance.
This is also the reason why demand for tin-free steel sheets is increasing.

However, this tin-free steel plate has a very big drawback of poor weldability, and currently it is exclusively made by bonding, or it is welded after removing the surface metal chromium and chromium oxide layer. The cans are made using the welding can-making method. Therefore, improving the weldability of tin-free steel sheets has great industrial significance. Various attempts have been made with the aim of improving the weldability of tin-free steel sheets, and the status of these technological improvements is summarized as follows.

(1) JP-A-62-124298, JP-A-31-1518, JP-A-58-127778, JP-A-513-44793, which improves weldability by plating the lower layer of the chromium plating layer with Sn, (2) X on the bottom layer of chrome plating layer
Unexamined Japanese Patent Publication No. 1982-1989 (1982-1999) was developed as an i-plated product with improved weldability.
40398, JP-A-62-107097, JP-A-81-
91393, JP-A-82-205297, (3) The chrome plating layer itself is devised (in many cases, the chrome plating is made protruding or discontinuous to reduce the resistance during welding). , Japanese Patent Publication No. 82-205297.
JP 82-99497, JP 63-35797, JP 82-83878. A large number of applications have been filed, such as JP-A-81-281899 and JP-A-81-213399. All of these are aimed at improving the insulation properties of the chromium plating layer and the chromium hydrated oxide layer to improve weldability.

Problems to be Solved by the Invention The present invention aims to improve weldability by plating the lower layer of the chromium plating layer in (1) with Sn, 1518. Japanese Patent Application Publication No. 5fl-12777fl, Japanese Patent Application Publication No. 58-44793,
# Below you need to lower the contact resistance! The amount of Sn plating is large, and in many cases the properties are only those of thin Sn-plated steel sheets, and the original properties of tin-free steel sheets are sacrificed in order to improve weldability.

In other words, although the weldability of tin-free steel sheets is improved in both cases, the inherent poor characteristics of tin-free steel sheets, such as metallic appearance gloss, excellent paint adhesion, and post-painting corrosion resistance, etc., are sacrificed. It cannot be said that it is an excellent surface-treated steel sheet for cans.

The problem to be solved by the present invention is to produce a steel sheet that is less expensive than tin plate, has good weldability, and can be produced at high speed without impairing the excellent properties of tin-free steel sheets, such as metallic appearance gloss, paint adhesion, and post-painting corrosion resistance. It is an object of the present invention to provide a method for manufacturing a surface-treated steel sheet that can be made into a can, without making any changes to conventional manufacturing equipment for tin-free steel sheets.

Means for Solving the Problems The present invention provides 5 to 20 g of divalent tin ions after degreasing the surface of a steel plate.
Pickling treatment is first carried out in a sulfuric acid pickling bath containing 130 to 150 gel/l of sulfur, and then 20 to 200 mg at a current density of 2 to 15 A/d with the steel plate as the cathode.
/ After tin plating, 1. Ordinary chrome plating.
Or 30~ by chrome plating and chromate treatment
1503 g/rn' of metallic chromium, 2 to 4 as chromium
This is a method for producing a surface-treated steel sheet with excellent weldability and paint adhesion, which is characterized by coating with 0 g/m' of chromium oxide.

The present invention will be explained in detail below.One feature of the present invention is that 5 to 20 g of divalent tin ions are added to the sulfuric acid pickling bath.
The purpose is to carry out tin plating at the same time as pickling in a bath containing fLm.

In other words, as seen in Japanese Patent Application Laid-Open No. 82-124298, many attempts have been made to improve the weldability of tin-free steel sheets by applying tin plating to the lower layer of the chrome plating layer. In the present invention, divalent tin ions are added to a pickling bath containing a large amount of iron ions, and metal tin is precipitated on the surface of the steel sheet at the same time as pickling. It was discovered that the weldability of ordinary tin-free steel plates can be improved by this method, and the weldability of tin-free steel plates has been improved at an extremely low cost without adding a tank for tin plating or additional equipment. It is something.

Furthermore, in the present invention, the tin plating obtained in the pickling bath is 0.2
A major feature is that it is granular with a particle size of ~1.5 p. That is, in conventional tin plating, it is necessary to uniformly cover the surface of the steel plate with tin, and it is desirable that the iron ion concentration in the tin plating bath be low, and generally, 10g1
It is considered to be below IL, and at most 15 g/cross. or,
In order to obtain uniform adhesion, additives called brighteners (in the phenolsulfonic acid bath, α-ethoxynaphthol, α-
-ethoxynaphenol, etc.) are used.

However, 1. In the present invention, divalent tin ions are added to the pickling bath, and in this bath, five grains of tin are precipitated due to the presence of many iron ions. It was discovered that the weldability of the steel was significantly improved.

Therefore, according to conventional wisdom, it was considered difficult to use tin plating for pickling and recycling, but rather, cathodic electrolytic treatment in a pickling bath that contains many iron ions and does not contain any brighteners. It has been discovered that the slightly salted tin plating layer produced by this method is effective in improving weldability, and a method for manufacturing a surface-treated steel sheet that has excellent weldability and has the excellent properties of a tin-free steel sheet has been discovered.

Figure 1 shows a scanning electron micrograph of a surface-treated steel sheet obtained by the method of the present invention, showing the presence of tin grains (the photo shows an average of 1.0 grains). I understand that.

Note that the pickling conditions at this time are as follows: Fe+23
5g/l, Sn+220g/l, 5O4-21
12g/41, pickling treatment conditions: bath temperature (19°C)
After immersion pickling treatment for 1.5 seconds, O.5 seconds
/da' cathodic electrolytic treatment, Gr0310
(tg/R1H7SO40.8g/l bath (bath temperature 50℃
)Inside,? OA/a weight 2 x 1 second ゛lL solution processing was performed.

The Sn adhesion rate of the obtained steel plate was 85 mg/111', and the average Sn grain size was 1. Jt, and the amount of chromium deposited was 120 mg/m' (metal Cr IX).

The content of the present invention and the reasons for the limitations will be explained in more detail below.

First, the divalent tin ion concentration in the pickling bath is 5 to 20.
The reason why it was limited to g1 is that below the limit value, the electromagnetic efficiency of tin plating will be less than 20%, and short-time cathodic treatment will not ensure the amount of Sn plating as specified in [4]. This is because if the limit value is exceeded, the uniformity of the Sn plating will be improved and granular tin plating with a size of 0.2 μm or more will not be obtained.

Next, the reason why the i acid concentration was limited to 30 to 150 g/cross will be explained. The F limit value was set at 30 g/u because if the concentration is less than this, the pickling of the steel plate will be insufficient, the adhesion of the subsequent tin plating will be poor, and chromium plating and chromate treatment may be difficult. This is because even if applied, the corrosion resistance after painting deteriorates. In addition, the reason why the limit value was set at 150 g/l is that if the concentration exceeds this, the current efficiency during tinning will decrease and the amount of tinning that is the IJ standard will not be obtained, thus improving weldability. I can't do that.

Next, the pickling treatment is not particularly limited.
It is sufficient to carry out the same pickling treatment as in the production of normal tin-free steel sheets; for anodic electrolytic treatment, 0.1 seconds or more is required, and for immersion treatment only, 0.5 seconds or more is required. . It may be determined as appropriate within the capacity of the pickling equipment. The present inventors investigated the effects of anodic electrolytic pickling and immersion treatment for up to 4 seconds, but no particular problem was found.

Next, the current density of tin plating, which is carried out subsequent to pickling, is set to 2.
The reason why it was limited to ~15A/da2 will be explained. If it is less than the lower limit, the current density of tin plating will be low, and the target amount of tin plating will not be obtained by short-time plating in a pickling tank, and weldability cannot be improved. , the tin particle size of the tin plating obtained is 0.2 l or less, and 2
Weldability could not be improved with a tin plating amount of 0 to 200 I1g/rI'1''.

Next, regarding the reason for limiting the amount of tin plating, a lower limit of 20 g/m'' is determined from the viewpoint of weldability.On the other hand, the upper limit is determined based on the characteristics of the tin-free steel plate, specifically.

It is determined to ensure properties such as surface appearance (color tone), paint adhesion, and corrosion resistance of paint. In other words, when the amount of tin plating increases, it begins to become granular.

Since the characteristics of tin-plated steel sheets appear and the excellent performance of tin-free steel sheets is impaired, the upper limit is set at 200 g/rt. Therefore, the optimal amount of tin plating is 20 to 200 mg/200 mg/ml as described above based on the required weldability, paint adhesion, paint tactility, etc.
It may be determined appropriately within the range of r'l'r'.

Next, chromium plating and chromate treatment method will be described.6 The present invention does not particularly limit these chromium plating and chromate treatment method.

In other words, chromium plating and chromate treatment can be carried out according to the ordinary method for manufacturing tin-free steel sheets, and the area ratio occupied by granular tin is 20% or less. Metallic chromium and a chromium oxide layer are formed in the exposed portions, resulting in properties equivalent to those of ordinary tin-free steel sheets.

Depending on the plating conditions, metal chromium may not precipitate on the granular tin, and only a chromium oxide layer may be formed, or vice versa, but within the scope of the research conducted by the present inventors, 1
The precipitation of chromium on the granular tin is slightly less than that on the exposed part of the steel plate, and even if chromium precipitates on the granular tin, the underlying tin has a thickness of 0.2 mm or more and there is no contact. It is estimated that this contributes to reducing resistance.

In other words, in the present invention, the state of chromium precipitation on the tin plating is not particularly restricted, and it is important that the exposed portion of the AT plate forms the original chromium plating layer and chromium oxide layer. For this reason, the amount of chromium plating layer and chromium oxide layer of the surface-treated steel sheet of the present invention is 30 to 1501 g/m' of metallic chromium, which is the range of general tin-free steel sheets, and 2 to 40 g/m' of chromium in the chromium oxide layer. The layer was limited to g/rn' (metallic chromium equivalent).

Generally, the amount of chromium in chromium oxide is 10mg/m'
This is to ensure adhesive strength in the adhesive can making method, and approximately 2 mg/m' is sufficient to ensure general paint adhesion, and seam welding It is preferable that the thickness of the chromium oxide layer, which has an adverse effect on properties, is as small as possible, and in the present invention, the lower limit of the amount of chromium (chromium oxide layer) is set to be slightly lower. Therefore, the amount of metallic chromium,
The chromium oxide acid may be appropriately selected within the above range depending on the can manufacturing method, contents, etc.

To summarize the features of the present invention again, it is effective to improve the weldability of tin-free steel sheets by carrying out single-grain (0.2 to 1.5 mm diameter) tin plating prior to chrome plating. The present inventors had previously discovered that, as an f-stage for obtaining such granular tin plating, 5 to 20 g/d of divalent tin plating was added to the pickling bath, and the steel plate was pickled before the acid addition step. 1. Next, by applying tin plating by cathodic electrolytic treatment, pickling and tin plating of the steel plate are carried out at the same time, and then chrome plating or chrome plating and chromate treatment is applied in the usual way to provide a surface treatment with excellent weldability. It provides a very economical method of manufacturing steel sheets.

EXAMPLES Next, the content of the present invention will be specifically explained with reference to examples, comparative examples, and conventional examples.

Example 1 A low-carbon cold-rolled steel sheet with a thickness of 0.23 mm that has been cold-rolled, continuously annealed, and temper-rolled by a conventional method is subjected to conventional degreasing (NaOH 50 g/i, 60° C., current density 10 A/min). d
After performing cathodic electrolytic treatment for 0.5 seconds at a2, immersion and anodic electrolytic pickling were performed in sulfuric acid pickling baths with different concentrations of divalent tin ions, followed by 0.5 seconds at a current density of 7 A/da2. 3
Samples of Examples, Conventional Examples, and Comparative Examples were manufactured by performing cathodic electrolytic treatment for 2 seconds, followed by chromium plating, and were evaluated.

1.M washing conditions (1) Bath conditions Sulfuric acid 100 ginSn”
O~30g/IL Fe" 20 tel Bath temperature 20℃ (2) Electrolysis conditions 1st stage 10A/d layer 2 Xo, 3 seconds, anode (steel plate) electrolysis treatment 2nd stage Immersion treatment 0.8 seconds 3rd stage 7A /da2X0.3 seconds, cathode (steel plate) electrolytic treatment (Sn plating) 2, chromium plating (1) bath conditions Gr03 100 g/view, H7SO,
1.2g/fL Bath temperature 50℃ (2) Plating conditions Current density 50A/d 2, 7fi air volume 50C/d Soda 2
3. Evaluation (1) Paint adhesion The test material was epoxy phenol paint (Kansai Paint ■,
SJ-11258) was painted and baked (pIiM amount 50 mg/
After da2), in 3.0% NaCl solution at 110°C x 60
(7) After performing the retort treatment, scratches were made with a knife in the base and a tape peeling test was performed (lO (good) ←
→l (defective)).

(2) Epoxyphenol paint (Kansai Paint■,
SJ-8258) was painted and baked (coating amount 50mg/da2)
), after making cross cuts with a knife on the paint film, 1.5
% NaCQ, 41% in 1.5% citric acid solution (40 °C)
] After that, a tape peeling test was performed on the cross-cut portion and evaluated (5 (good) ←→l (bad)).

(3) Contact resistance test material was first heat treated at 210°C for 30 minutes,
Cut into 50 mm square pieces, stack the two samples together, and sandwich them between electrodes with an electrode diameter of 4.5mm.
A pressure of 0 kgF was applied and the contact resistance was measured (the current passed between the electrodes was 1000 s^), and if it was 500 JLΩ or less, it passed (good weldability).

(4) Evaluation of tin plating grains Measure the sample material using a scanning electronic W411Ii mirror at a magnification of 5000~
Observe 2 representative leak sizes at 10,000x magnification.

(5) Product appearance Evaluation was made based on the appearance of the tin-free steel plate.

0 Equivalent to tin-free steel plate Almost equivalent to O-tin free steel plate X Different from tin-free steel plate.

Example 2 A low carbon cold rolled steel sheet with a thickness ξQ of 23 am that had been cold rolled, continuously annealed, and temper rolled by a conventional method was subjected to conventional degreasing (NaOH 50 gin, 60° C., current density 10 A).
/da2 for 0.5 seconds), followed by immersion and anodic electrolytic pickling in pickling baths with different sulfuric acid C degrees, followed by 0.5 second electrolytic treatment at 7 A/ds' and density. Samples of Examples and Comparative Examples were manufactured by performing cathodic electrolysis treatment for 3 seconds or 0.8 seconds, followed by chromium plating and chromate treatment, and were evaluated.

■, Pickling conditions (1) Bath conditions Sulfuric acid 20-180 g/JIS
n2÷ 10g1 Bath temperature 20℃ (2) Electrolytic conditions Cathode (steel plate) electrolytic treatment 2, chrome plating (1) Bath conditions CrO3too gin, H2SO
40.2g/1 bath temperature 50℃ (2) Plating conditions Current density 50A/da2. tliki13150C/d
a23, Chromate treatment (1) Bath conditions CrO350g/l, H2SO40,1
M bath temperature 50°C (2) Processing conditions Current density 10A/da2. Electricity: 10 c/d Maro 2 (hereinafter referred to as blank space) Example 3 A low carbon cold rolled steel plate with a thickness of 0.23 cm was cold rolled, continuously annealed, and temper rolled by a conventional method.

Normal degreasing (NaOH50gel, 80℃, current density 1
After performing cathodic electrolysis treatment for 0.5 seconds at 0A/d set 2,
After immersion and anodic electrolytic pickling in a pickling bath with a sulfuric acid concentration of 50 g/i, 0
．． Samples of Examples and Comparative Examples were manufactured by performing cathodic electrolysis treatment for 3 seconds to 0.6 seconds, followed by chromium plating and chromate treatment, and were evaluated.

1. Pickling conditions (1) Bath conditions Sulfuric acid 50g/Sn” 1
ogin Bath temperature 20℃ (2) Electrolytic conditions 1st stage 10A/da2X0.3 seconds, anode (steel plate) electrolytic treatment 2nd stage immersion treatment 0.8 seconds 2, chromium plating (1) Bath conditions Cr03too gel, 1 (zso
, 1.2g/fL Bath temperature 50°C (2) Plating conditions Current density 50A/da2. Electricity amount 50G/da23, chromate treatment (1) Bath conditions CrO350gel, 11,5O40,
1 g/l bath temperature 50°C (2) Processing conditions Current density 10 A/d 2, quantity of electricity 10 C/d 2 (blank below) Effects of the invention At step i11, after degreasing, in a pickling solution to which -valent tin ions were added, cathodic electrolysis treatment was performed in the same bath following pickling, without making any changes to the conventional manufacturing equipment j1. A surface-treated steel sheet was obtained very economically, which maintained the excellent appearance, paint adhesion, and rIIA corrosion resistance of a tin-free steel sheet, and was also excellent in high-speed seam welding +1.

[Brief explanation of drawings]

FIG. 1 is a photograph substituted for a drawing taken with a scanning electron microscope of the appearance of a metal structure after tin plating obtained by adding monovalent tin ions to a pickling bath.

Claims (1)

[Claims] (1) After degreasing the surface of the steel plate, 5 to 20 g/l of divalent tin ion
In a sulfuric acid pickling bath containing 30 to 150 g/l of sulfuric acid, first pickling treatment, then 2 to 15 A/dm^ using a steel plate as a cathode.
After tin plating with a current density of 20 to 200 mg/m^2 at a current density of 2, 30 to 150 mg/m^2 of metallic chromium, 2 to 40 mg/m as chromium, by regular chromium plating or chromium plating and chromate treatment. A method for manufacturing a surface-treated steel sheet, characterized by coating with chromium oxide of ^2.