JPS5852495A - Steel plate for vessel - Google Patents

Abstract

PURPOSE:To obtain a steel plate for vessel which lends itself to a can making system by welding or deep drawing and has excellent corrosion resistance and painting performance by forming an Ni-Sn plating layer and a chromate film layer of specific coating weights successively on the surface of the steel plate. CONSTITUTION:An Ni-Sn alloy plating layer of 50-1,000mg/m<2> per side is formed on the surfaces of a steel plate, and a chromate film layer of 3-30mg/ m<2> per side in terms of Cr is formed on the surfaces of said plated layer. Here, the Ni-Sn alloy has much better corrosion resistance than Ni or Sn and can therefore reduce the thickness of the plating layer. This alloy is lower in m.p. than Ni and improves weldability by electric resistance. Since said alloy has a higher m.p. than Sn, the blackening of weld zones by welding heat and the degradation in corrosion resistance and painting performance are prevented. The chromate film layer on the plating layer prevents corrosion from unavoidable pinholes when said alloy plating layer is thin, and further the layer prevents the elution of the plating layer per se and improves painting performance.

Description

[Detailed description of the invention] The present invention relates to a steel plate for containers.

In recent years, can making methods by welding (e.g. Sudronik melting process) or can making methods by drawing (e.g. DI
Processing methods) are diversifying and showing remarkable progress. Also,
There is a demand for inexpensive can-making materials (container materials) with excellent performance that can be used in these can-making methods. In order to meet these requirements, it is necessary to have excellent weldability and drawing and ironing workability (corrosion resistance against can making tools), as well as the performance required for container materials, namely corrosion resistance, paint adhesion, and corrosion resistance after painting. It must be a combination of the following.

Conventionally, tinplate and electrochromic acid treated steel sheets (TFS) have been widely used as materials for containers. However, the materials for the new method of can manufacturing are limited by price, weldability, corrosion resistance,
There was still room for improvement in terms of moldability and coating performance. That is, when tinplate material is welded, Fe in the base metal diffuses into the molten metal to form an Fe-Sn alloy, and the surface of this alloy is significantly oxidized. For this reason, the welded portion and the heat-affected zone in its vicinity turn black, impairing its appearance and deteriorating its corrosion resistance and paintability.

Furthermore, in the can manufacturing method by drawing, for example, in the manufacture of DID cans, the paint adhesion after can manufacturing is not necessarily satisfactory.

On the other hand, electrolytic chromic acid treated steel sheet (T
FS) is widely used and has excellent economic efficiency and cost. However, TFS is composed of a chromate film consisting of metallic chromium and chromium oxide mainly composed of hydrated chromium oxide.

Therefore, as is known from the past, these metal chromium and chromate coatings are metals or oxides that are difficult to weld, so when welding is used to make cans, the strength of the welded part is often insufficient. . Therefore, when using TFS as a material for welded cans, TFS corresponding to the welded part
A commonly used method has been to mechanically grind and remove the FS surface to manufacture welded cans.

However, with this method, the TFS is approximately 70 to 150 per side.
119/m' metal Cr layer and about 10-309 on this surface.
/. Since it is generally formed of a chromate film layer of There are also many problems with the method of grinding and removing the TFS surface, such as contaminating the outer surface.

In addition, when this electrolytic chromic acid treated steel sheet is subjected to drawing processing, for example DI processing, part of the metal Cr is fused to the tool due to the friction of the tool ♂, resulting in subsequent (linear scratches on the product). There are disadvantages such as the occurrence of so-called galling phenomenon and deterioration of appearance corrosion resistance.

This invention was made in order to improve the above-mentioned drawbacks of conventional container materials, and provides an inexpensive steel sheet for containers that can be made by welding or drawing, and has excellent corrosion resistance and painting performance. This is what we are trying to provide.

The steel plate for containers of this invention has a capacity of 50 to 1000 ql per side.
An alloy plating layer consisting of Ni and Sn is formed with a coating amount of 3 to 31) m2 per side on the surface of this alloy plating layer.
51/rr? A chromate coating layer is formed.

Further, it is preferable that the metal chromium layer of the above-mentioned chromate coating layer has a thickness of 15 .mu./d or less per side.

Plating with a Ni-Sn alloy consisting of Ni and Sn provides the following advantages.

As is conventionally known, Ni-Sn alloys have significantly better corrosion resistance than Ni or Sn.

In particular, when steel sheets plated with Ni-Sn alloys are used as container materials, they have extremely good corrosion resistance against CX- and organic acids, which exhibit strong corrosive effects and are often contained in can contents. There is. Therefore, the thickness of the plating layer can be made thinner, thereby reducing the thickness.

The melting point of the spun Ni-Sn alloy is lower than that of Ni due to alloying with Sn, and the weldability due to electrical resistance is improved.In other words, the low melting point makes it easy to form nuggets. As mentioned above, the Ni-Sn alloy solidifies faster than Ni because it has a lower melting point.

Therefore, during welding, welding defects caused by molten metal flying out from the welded part (weld part) before solidification, so-called "splatter", are significantly less likely to occur.

Furthermore, the Ni-8n alloy has a higher melting point than Sn. Therefore, due to welding heat, Fe
- Blackening of the weld zone and deterioration of corrosion resistance and coating performance caused by the formation of Sn-based alloys are prevented.

In this invention, as described above, a chromate coating layer is formed on the surface of the Ni--Sn alloy layer. Formation of the chromate film layer produces the following effects.

When the Ni-Sn alloy plating layer is thin, the occurrence of bottle holes is unavoidable and the corrosion resistance deteriorates. The chromate coating layer prevents corrosion from such holes and further prevents the plating layer itself from being leached. Therefore, corrosion resistance is further improved.

Also, most of the containers made using the steel plate of this invention are lacquered. Ni-Sn alloy plating material is
Painting performance is poor due to the oxide film that forms on the surface of untreated wood. Coating performance can be improved by forming a chromate film layer on the plated surface.

At the same time, the conditions and treatment methods necessary for the Ni-Sn alloy plating and chromate coating to produce the above effects will be explained.

The adhesion amount of Ni-Sn alloy plating layer is I~1 per side.
000 q/rn', preferably 100-500 q/
Must be ni'. Adhesion amount is 50gg/r
r? Corrosion resistance deteriorates due to the occurrence of many cracks/holes that are less than 100 mm. Also, the amount of adhesion is 1000 W/rr? If it exceeds this value, the corrosion resistance effect will be saturated and the cost will increase.

Regarding the alloy composition of Ni and Sn, according to the experimental results, S
It is desirable that n is 15 to 90%, preferably 60 to 80%, and particularly preferably a NiSn alloy composition (approximately 65% Sn), which has particularly excellent corrosion resistance in Ni-Sn alloys. If the Sn content is less than 15, the melting point of the alloy will not decrease significantly and the weldability will not improve significantly. Also.

When Sn exceeds 9096, the melting point of the alloy decreases significantly,
The diffusion of Fe from the plated original plate is significant, resulting in discoloration of the weld zone and heat-affected zone, and deterioration of corrosion resistance and paintability.

In addition, when the alloy composition is within the above range, the corrosion resistance of the steel plate,
If the temperature is lower than that, the performance after painting will also be improved. That is, as mentioned above (Ni-Sn alloy has good corrosion resistance and a low corrosion rate, so if it is exposed to a corrosive aqueous solution for a long period of time after painting, the corrosion rate of the corrosive aqueous solution that penetrates through the coating film is extremely low, and the corrosion rate is extremely low. Performance deterioration such as blistering (so-called blistering) and peeling of the paint film due to corrosion products on the surface is extremely likely to occur.

As the plating bath, a commonly used Ni--Sn alloy electroplating bath is used. For example, a pyrophosphoric acid bath, a chloride bath, a fluoride bath, etc. in which Nr and sn+ are co-contained are used.

The amount of chromate film is 3~ (capital) per side in chromium equivalent amount.
W/m2. Preferably it should be 5-201 nQ/m'. The chromate film may be composed only of a chromium oxide film mainly composed of water-containing chromium oxide,
Alternatively, it may be composed of a metal chromium layer and a chromium oxide coating mainly composed of water-containing chromium oxide formed on the surface of the metal chromium layer.

If the amount of chromate coating is less than 3"f/m', the effect of improving the corrosion resistance and coating performance of the alloy plating layer cannot be obtained.

When the amount of chromate coating exceeds 301197 m', the effect of improving corrosion resistance and coating performance becomes saturated.

The following problems arise in terms of performance. In the case of the can-making method by welding, weld nuggets are not sufficiently uniformly generated during electric resistance welding, and "splashing" occurs significantly, making it impossible to obtain the required welding strength. In addition, in the case of a can manufacturing method using drawing, when the amount of chromate coating increases, a part of the chromate coating sometimes peels off during the drawing and ironing process, resulting in deterioration of its corrosion resistance.

When a metallic chromium layer is formed in the chromate coating layer, the amount of the metallic chromium layer is 15 μ/- or less, preferably 1
Experiments have shown that a thickness of 097 m2 or less is effective in improving weldability and drawing workability.

That is, when a large number of metallic chromium layers are formed, the high melting point prevents the formation of uniform nuggets, and the metallic chromium is fused to can-making tools (dies, punches, etc.) by DI processing, and then processed. causing linear scratches on the product.
The so-called galling phenomenon occurs frequently.

Formation of the chromate film is performed under the following conditions.

The chromate treatment bath is an aqueous solution of chromic acid anhydride, chromate (ammonium chromate, chromate sorter, etc.), dichromate (ammonium dichromate, potassium dichromate, etc.), or an anion (SO4 ”-2, F-
etc.) is used. In particular, the addition of anions can be done by cathodic electrolytic treatment in the chromate treatment bath, and by selecting an appropriate current density, the pinholes in the Ni-Sn alloy layer are blocked by the precipitation of a metallic chromium layer, which improves corrosion resistance. Improve further. However, since the addition of anions produces a large metallic chromium layer that has a negative effect on weldability or galling resistance, the chromate treatment conditions must be adjusted so that the amount of metallic chromium layer is 15 μm/m2 or less. It is necessary to make a selection.

The appropriate concentration of the chromate treatment bath is 10 to 150 Vl. If the concentration is less than 1 og/I), it is unfavorable in terms of stability and aging properties of the treatment bath. Also, the concentration is 150
If Vl is exceeded, the effect of improving corrosion resistance and the like is saturated, and a large amount of the processing bath is carried out by the plated plate, which is uneconomical.

Chromate treatment is carried out by cathodic treatment or a combination of cathodic and anodic treatment. The current density and processing time are selected to obtain the required coating amount, usually when the current density is 5~
30 A/dm2. Processing time is 1 to 3 seconds. For example, CrO3-5O4-2 ice bath (SO4-2/Cr+6
-1150), when the current density is 30 A/dm2 or more, the precipitation of metallic chromium is significant, and it is difficult to suppress the precipitation of metallic chromium to 15 T/i or less even with extremely short treatment. Further, the temperature of the treatment bath is usually in the range of @ to 90°C.

Next, after the chromate treatment as described above or after washing with water,
Washing with high-temperature water having a temperature of 5° C. or higher and a pH of 4 to 10 is effective in further improving the performance after chromate treatment.

That is, this high-temperature water treatment removes anions such as SO4"-2 or Cr+6, which are water-soluble components in the chromate film.
Corrosion resistance after painting increases by leaching out.

That is, in the Ni-8n alloy plated and chromate-treated steel sheet washed with water as described above, the components that are easily eluted from the chromate coating are reduced. Therefore, after painting,
Even when a steel plate is exposed to a corrosive aqueous solution, blistering of the paint film caused by water-soluble components is less likely to occur, and defects such as paint peeling become thicker (reduced).

In this high-temperature water treatment, the temperature and conditions are specified for the following reasons: In the high-temperature water treatment, the Cr contained in the chromate film.

This is carried out to remove anions such as SO4''-2 ions from the chromate coating and to promote dehydration and condensation reactions of the chromate coating made of colloidal Cr hydroxide.

Therefore, in order to achieve the above effects at high speed and in a short period of time, it is preferable to specify the temperature or pH as described above.

If the value is less than 4, it is undesirable because the elution of anions such as Cr+6 or 5o4-'' in the chromate film will be hindered.If the value is less than 10, the chromate film may be dissolved, so the pH]o The following will be used:

In particular, when elution rate is considered, a pH range of 6 to 9 is most preferable;
Adjustments may be made.

In addition, the temperature of the water used for this treatment is 65 to 100°C,
Preferably high temperature water of 70-95°C is used.

A'lJ: In order to elute and remove water-soluble components from the chromate film by high-speed, short-time processing, high-temperature treatment is of course necessary, and in addition to these elutions, hydroxylation of colloidal Cr. High-temperature water treatment at the above-mentioned temperature is preferred in order to accelerate the dehydration and condensation reaction of the chromate film made of the chromate film and form a poorly soluble chromate film with a low degree of hydration, that is, a high degree of oxidation.

Regarding the treatment time, unless the treatment time is 0.3 seconds or more, elution treatment from the chromate film, especially Cr+6
The elution of the chromate film is not sufficient, the degree of oxidation of the chromate film is not sufficiently improved, the desired effect of the present invention cannot be obtained, and a treatment time of 10 seconds or more is not industrially economical (, The treatment time is limited to 10 seconds or less because re-penetration of anions such as SO4'' in the water used or other impurities contained in the water causes the chromate film to contain components that are easily eluted.

As for the method of applying high-temperature water, any of immersion treatment, spray treatment, and injection treatment with hot water mixed with high-temperature steam and low-temperature aqueous solution may be used as long as the above-mentioned conditions are satisfied.

In addition, in the present invention, even if metal ions contained as inevitable impurities in the plating bath are electrodeposited and contained in the plating layer, it is within the scope of the present invention. For example, Co, which is often contained as an unavoidable impurity in Ni metal, is contained in the plating layer, but such cases do not depart from the scope of the present invention.

Examples of the present invention will now be described.

Table 1 compares and compares the test results of weldability, etc., performed by plating and chromate coating under various conditions. Each performance was evaluated as follows.

(1) Evaluation of corrosion resistance After a sample was immersed in 0.5M tartaric acid at 5°C for 48 hours, the corrosion loss was measured.

(21 Evaluation of Weldability Steel plates were welded by a method (Suudronik type) in which a copper wire (approximately 1.5 mm in diameter) was moved and overlapped under pressure as an electrode for electrical resistance welding (Sudronik type).
The weldability was evaluated within the range of current and pressure in which uniform nugget formation and sufficient welding strength were obtained. In addition, the appearance of the welded part was evaluated based on the degree of discoloration of the welded part and the vicinity of the welded part due to thermal effects during welding.

(3) Performance evaluation after coating After coating with an epoxy phenol paint to a thickness of 4.5 μm, the sample was immersed in an air-saturated aqueous solution containing 1.5% NaCI) and 1.5% citric acid for 96 hours.

Secondary paint adhesion was evaluated using a goblin test.

In addition, a scratch was made on the painted surface, and the corroded state of the scratched portion after the above-mentioned immersion was used to evaluate the corrosion resistance of the material after painting.

(4) Scratching the same area repeatedly using a Bowden friction tester,
Evaluation was made based on the number of times of rubbing until the friction coefficient suddenly increased.

The test conditions were as follows: the tip was a 10 mm diameter steel ball, the load was 50og, and the rubbing speed was 1000 m/min.

Note that the evaluation symbols in Table 1 indicate the following contents.

Claims (1)

[Claims] 1. An alloy plating layer consisting of Ni and Sn with a strength of 50 to 1000 W/m' per side is formed on the surface of the steel plate, and a maximum of 3 to 30 W/m' per side in terms of Cr is formed on the surface of this alloy plating layer. ■／
A steel plate for a container, comprising a steel plate strip on which a male chromate film layer is formed. 2. The steel sheet for containers according to claim 1, wherein the metal chromium layer formed within the chromate coating layer has a concentration of 15 Mg/m' or less per side. 3. The steel plate for a container according to claim 1 or 2, wherein the container is a welded can. 4. Claim 1, wherein the container is a processing can.
The steel plate for containers according to item 1 or 2.