JPS6379994A - Production of steel sheet for welded can - Google Patents

Abstract

PURPOSE:To produce a steel sheet for a can having superior weldability and corrosion resistance by thinning the surface of a steel sheet to form a coarse- grained Sn layer, carrying out reflow treatment and successively depositing metal Cr and chromium oxide hydrate. CONSTITUTION:A steel sheet is tinned with a bath contg. about 40g/l stannous sulfate and about 80g/l sulfuric acid at about 30 deg.C and about 5-20A/dm<2> current density to form a coarse-grained Sn layer having about 0.1-0.3mu grain size on the surface of the steel sheet by about 0.1-1.2g/m<2> per one side. Reflow treatment is then carried out at about 213-300 deg.C for about 0.5- several sec to form a nearly uniform Xn-Fe alloy layer on the steel sheet and about 0-30mg/m<2> metal Cr and about 2-30mg/m<2> (expressed in terms of Cr) chromium oxide hydrate are successively deposited on the Sn-Fe alloy layer. Thus, a steel sheet for a welded can is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a steel plate for welded cans.

[Prior art and problems to be solved by the invention] As steel plates for welded cans, for example, there are known steel plates in which chromium hydrated oxide or metallic chromium and chromium hydrated oxide are formed on a tin-plated steel plate. (Japanese Patent Application Laid-open No. 55-69297).

In such steel plates, heating during painting baking causes
An alloy layer of steel plate (iron) and tin is formed below the tin plating layer,
This is accompanied by drawbacks such as deterioration of weldability. It is also known to apply coarse grained tin plating to a steel plate and form a hydrated chromium oxide on the top layer (Japanese Patent Laid-Open No. 67,677/1983). Although such steel plates have good weldability, they have drawbacks such as a slight decrease in corrosion resistance.

[Means for solving problems]

The present invention was made to advantageously solve these drawbacks, and its characteristics are that coarse grain tin plating is applied to the surface of the steel plate, then reflow treatment is applied, and the upper layer is coated with chromium hydrated oxide. 1. A method for producing a steel plate for welded cans, characterized by producing a product.

The present invention also relates to a method for manufacturing a steel plate for welded cans, which comprises applying coarse-grain tin plating to the surface of the steel plate, then subjecting it to reflow treatment, and sequentially forming metallic chromium and chromium hydrated oxide on the upper layer.

[Effect]

In other words, chromium-plated steel sheets have poor weldability, and as a countermeasure to this, tin plating is applied to the base, and when the base is heated during welding, tin, which has good conductivity and a low melting point, melts before the chromium, reducing the welding pressure. The metal chromium, etc. on the upper part are discharged from the welding area together with the molten tin, thereby eliminating welding defects caused by metal chromium, etc.

However, tin plating is applied as a base for chrome plating.
Electroplating is performed using a generally known industrial tin plating bath, such as a ferrostane bath, but in such tin plating, even when observed under a microscope with a magnification of 10,000 times, crystal grains are hardly visible. Densely plated. Therefore, when the amount of tin plating is less than 0.5 g/rrf, or when the heat load during paint baking is large, iron-plating occurs at the boundary between the steel plate (iron) and the tin plating layer due to the heating during paint baking.
A large amount of tin alloy layer is formed (almost fully alloyed), and therefore metallic tin (free tin) is reduced or eliminated, which makes it difficult to discharge metallic chromium etc. from the weld zone, resulting in poor weldability. This will result in a lower level of performance.

In addition, if the tin-plated metal is made into coarse grains so that the contact with the steel plate is rough, and if the local amount of tin adhesion is increased, that is, if it is brought into porous contact, as mentioned above, due to the heating during paint baking, , the alloying of iron and tin at the bottom of the tin plating layer remains, that is, the alloying remains at the bottom of the tin grains, and free tin remains securely, and due to the fusion contact of the free tin remaining during welding,
It is possible to reliably discharge metallic chromium, etc., and there is less iron-tin alloy layer at the discharge site (welding part), so weldability can be improved, but the tin is coarse grained and cannot be painted. The heating during baking only alloys the lower end of the coarse tin, and therefore the tin-iron alloy layer is also interrupted, resulting in poor corrosion resistance. Therefore, in the present invention, after coarse grain tin plating, reflow treatment is performed at, for example, 231 to 300°C for 0.5 to several seconds to form a nearly uniform tin-iron alloy layer on the steel plate, and the upper layer is By processing the steel so that coarse grained tin is present, a steel sheet for cans with excellent weldability and corrosion resistance can be obtained.

However, in this tin-plated metal, the crystal grain size of the deposited tin is 0.
If the crystal grain size is coarsened to 1 to 0.3μ, the objective can be achieved.If the crystal grain size is about 0.1μ or less, for example, if the amount of tin deposited is 0.5 g/m, the above reflow treatment will reduce the alloy. The layer becomes large, there is almost no free tin, there is little improvement in weldability, and if the crystal grain size is about 3μ or more, it is possible to solve the problem of welding. The adhesion and appearance of the plating deteriorate, which is undesirable. The amount of plating is 0.1 tin per side.
~1.2 g/bo is sufficient.

After such coarse grain tin plating, the above-mentioned reflow treatment is performed, followed by electrolytic chromic acid treatment or cathodic electrolysis treatment in a bath mainly composed of sodium dichromate, which is used in electric tinplates. This film has a metallic chromium content of 0 to 30 mg/rtr, and an upper layer of chromium water-conserving oxide (Cr content in the oxide) of 2 to 30 mg/rtr.
A steel plate for welded cans is produced by generating mg/rd. Metal=4- Even if the amount of chromium exceeds 30 mg/m, no particular advantage in corrosion resistance performance can be found, and the disadvantage of lowering welding performance becomes greater. Also, the amount of chromium in the chromium hydrated oxide film is 3
If it exceeds 0 mg/m, the surface appearance of the plated plate will take on a yellowish tinge, impairing its commercial value, as well as impairing paint adhesion and welding performance, which is not preferable.

As a method for applying coarse grain tin plating, for example, sulfuric acid
- Tin 40 g/Q, sulfuric acid 80 g/Q, bath temperature 3
Plating can be performed reliably at 0°C and a current density of 5-2 OA/dm.

Furthermore, in the present invention, when it is necessary to improve surface gloss and corrosion resistance when manufacturing steel sheets for welded cans as described above, ordinary dense tin plating is applied on the granular tin plating layer. The amount is 0.1~], , 2 g/
rd is sufficient to achieve the purpose, and then reflow treatment is performed, and by precipitating chromium hydroxide oxide or metallic chromium and chromium oxide on the upper layer as described above, welded cans with superior surface gloss and corrosion resistance can be produced. It is also possible to produce steel sheets for industrial use.

〔Example〕

Next, examples of the present invention will be listed together with comparative examples.

Welding conditions Using a varnish-dronic welding machine, welding speed 23
．． 5 m/min, lap 1110, 8 mm, pressing force 5 Q k, g.

The welding was conducted at a current (primary side) of 21 A to investigate the occurrence of dust during welding.

Dust: Less than 1 dust on the welded part on the inner surface of the can per 10 cm of can length. ◎, 2-40, 4-8△, ×9 or more. (Steel plate 0.
1. Plating was applied to a thickness of 23 mm, and after dry firing at 210° C. for 20 minutes, a welding test was performed. ) Corrosion resistance 5UCC (corrosion rl] m/m) Epoxyphenol paint applied to plated steel plate at 55 mg/m
After coating and baking at 210'C for 10 minutes, a cross pattern appears on the surface.
Place the knife into a knife cutter 1 with a width of 1-0μ and a depth of 15μ, and place it in a corrosive solution consisting of 1.5% citric acid and 1.5% di-salt at 50°C.
×3E old 111 was immersed and the spread of rust from the cut portion was investigated.

Coarse grain tin plating: Sulfuric acid No. Lt 140 g/Q, sulfuric acid 75 g/D.

Conducted at bath temperature of 30°C, current density of 15 A/d rrr.

Performed using a ferrostane bath commonly used for ordinary tin plating.

Chromium treatment is carried out by cathodic electrolysis in a commonly used plating bath.

〔Effect of the invention〕

By doing so, the weldability of the chromium-treated steel sheet can be significantly improved. Further, excellent effects such as improved corrosion resistance and gloss can be obtained.

Claims (2)

[Claims] (1) A method for producing a steel plate for welded cans, which comprises applying coarse grained tin plating to the surface of the steel plate, followed by reflow treatment, and forming hydrated chromium oxide in the upper layer. (2) A method for manufacturing a steel plate for welded cans, which comprises applying coarse grain tin plating to the surface of the steel plate, then subjecting it to reflow treatment, and sequentially forming metallic chromium and chromium hydrated oxide on the upper layer.