JPS6299497A - Manufacture of electrolytically chromated steel sheet for welding - Google Patents

Abstract

PURPOSE:To easily manufacture an electrolytically chromated steel sheet having superior weldability by temper-rolling an electrolytically chromated steel sheet at a proper draft to crack the chromate film and by carrying out tinning by a proper extent of sticking. CONSTITUTION:An electrolytically chromated steel sheet obtd. by forming a chromate film consisting essentially of metallic chromium and chromium oxide hydrate on the surface of a steel sheet is temper-rolled at 2-20% draft. By this rolling, the chromate film is innumerably cracked so that the cracks reach the base iron. The surface of the steel sheet is then tinned to form a tin layer by 5-600mg/m<2> extent of sticking per one side. The tin layer has satisfactory adhesion and part of the layer reaches the base iron. Thus, an electrolytically chromated steel sheet suitable for use in the manufacture of a welded can be electric resistance seam welding is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electrolytic chromate-treated steel plate for welding, specifically,
The present invention relates to a method for manufacturing electrolytic chromate-treated steel sheets suitable for welded cans manufactured by electric resistance seam welding.

Electrolytic chromate treated steel sheet with a film mainly composed of
TFS-CT) is a 2-piece can made by drawing process or a bonded mortar (3-piece can) using organic resin or special cement.
Due to its excellent paintability and corrosion resistance, it is widely used in food cans such as beverage cans, miscellaneous cans such as bale cans, 181 cans, and oil cans, and in many other fields.

Among the recent diversification of can manufacturing methods, for example, a method for manufacturing can bodies using electric resistance seam welding such as sudronik welding has been significantly developed. Therefore, a surface-treated steel sheet for can manufacturing that is suitable for welding is increasingly desired. However, the weldability of the electrolytically chromate-treated steel sheet is significantly inferior to that of unplated steel sheet or tin-plated steel sheet, and this makes it difficult to expand the use of this type of steel sheet.

The main reason for this poor weldability is the surface film of the electrolytically chromate-treated steel sheet. That is, when ordinary TM chromate-treated steel sheets are resistance seam welded, the chromium oxide forming the surface becomes an insulating film, increasing the contact resistance at the lap portion of the longitudinal edge of the can body. As a result, heat generation becomes uneven, causing the steel to generate heat locally, causing dust,
An undesirable cavity (blowhole) may be formed in the weld nugget. Furthermore, if these defects are avoided, the appropriate range of welding current becomes extremely narrow, making it difficult to stably perform welding operations, making it impossible to perform reliable welding.

[Means to solve the problem]

In view of the above-mentioned conventional problems, the present inventors conducted various studies with a view to lowering the contact resistance of electrolytic chromate-treated steel sheets, and as a result, they found that when electrolytic chromate steel sheets were subjected to temper rolling, cracks occurred in the coating. It has been found that contact resistance can be significantly reduced by applying tin plating on the chromate film.

That is, in the present invention, the electrolytic chromate treated steel sheet is rolled at a rolling reduction rate of 2.
The chromate film is temper-rolled at ~20% to cause cracks, and then the coating amount per side is reduced to 50~20%.
Its basic feature is that it is plated with tin at a rate of 600~/m1.

The present invention will be explained in detail below.

In the present invention, cracks are generated on the chromate film surface of the electrolytically chromate-treated steel sheet, and some of these cracks also occur in the underlying metal chromium layer, even reaching the base steel. The cracks generated in this way are effective in increasing the local destructive effect caused by the pressure applied during welding and making it easier to flow a uniform welding current. (contact resistance) hardly decreases.

In the present invention, after the above-mentioned temper rolling, the steel plate is tin-plated so that metallic tin adheres to the surface of the chromate film where cracks are present, thereby significantly reducing the contact resistance and obtaining a good welded joint. .

Tin is soft and a good conductor, and in the present invention, these characteristics of tin are utilized to improve contact resistance.Normally, tin is plated on an electrolytically chromated steel plate (strictly speaking, on a chromochromate layer). Tin has very poor adhesion, making it impossible to obtain stable plating.However, when tin plating is applied after temper rolling, which causes numerous cracks, some of the tin gets into the cracks. Furthermore, some of the tin penetrates into the cracks that reach the base steel and becomes involved in close contact with the iron, resulting in the adhesion of the tin that has entered the cracks, and furthermore the adhesion of the tin that has adhered to the electrolytic chromate treatment film. Improve power.

Since the tin deposited in this way is soft and conductive, it fills in the gaps created by the roughness of the steel plate when welding pressure is applied, resulting in uniform contact resistance and cracking. Since the welding current easily flows to the base metal through the tin inside, a welded can that does not induce defects in the welded part can be obtained.

The temper rolling of the electrolytic chromate treated steel sheet in the present invention is as follows:
It is carried out at a rolling reduction of 2 to 30 degrees.

If the rolling reduction ratio is less than 2 degrees, cracks in the chromate film will not be sufficiently generated, so that sufficient improvement in contact resistance will not be observed, and the adhesion of the attached tin will be insufficient. On the other hand, the reduction rate is 2
If it exceeds 0%, cracks on the surface will become too large, creating a striped pattern that gives the impression of surface destruction, resulting in an inconvenience in appearance. Note that even if the reduction ratio exceeds 15%, the weldability after tin plating is only slightly improved, and therefore the preferable range of the reduction ratio is 2 to 15%.

The amount of metallic tin deposited on the tin plate after temper rolling is 50 to 600 W/m'' per side.

If the amount of tin deposited is less than 5097 m'', no effect of improving weldability due to tin is observed.On the other hand, if the amount of tin deposited exceeds 600 m9/m'', no further effect of improving weldability is observed. The target electrolytic chromate-treated steel sheet is one that has been found to have value as a surface-treated steel sheet that does not use expensive tin, so any amount of tin deposited higher than that would impair economic efficiency and deviate from the purpose of the present invention. It turns out.

FIG. 1 shows the relationship between the amount of tin deposited and the contact resistance when temper rolling is performed at a reduction rate of 10%.

Metal tin plating methods include dry plating such as vacuum evaporation, electroplating or chemical plating in a tin-containing solution, gas type or electric spraying, and any of these methods may be used. can. Tin plating can be applied to both sides or one side of the steel plate.

Further, after tin plating, the adhered tin may be melted. Through this melting process, some of the tin that has reached the base metal becomes alloyed, which increases the contact resistance somewhat, but the molten tin also enters into the cracks and fills them further. , the adhesion is further improved.

Furthermore, by performing the melting treatment, the color of the surface, which had been whiter than that of the tin that had been deposited, approaches the color of the original electrolytically chromate-treated surface.

Further, the steel plate after plating can be subjected to chemical treatment such as electrolytic treatment in a chromate bath solution or immersion treatment.

〔Example〕

Next, the present invention will be explained in detail.

After temper-rolling the electrolytic chromate-treated steel sheet, electrolytic tin plating was applied in a ferrostane bath to produce an electrolytic chromate-treated steel sheet according to the method of the present invention. Then, the treated steel sheet manufactured in this manner was exposed to 210'OX for 10 minutes, and the contact resistance was measured. In addition, the steel plates were subjected to a Sudronitsta welding machine to examine weldability. Also, as a comparative example, conventional! The contact resistance and weldability of the chromate-treated steel sheets and the electrolytic chromate-treated steel sheets subjected to temper rolling were also examined in the same manner. The results are shown in Table 1 along with the manufacturing conditions.

The weldability was evaluated using a Sudronik welding machine.
Comprehensive evaluation was conducted based on the width of the suitable welding current range, weld appearance, and weld strength.

The scores are as follows.

◎...Remarkably good ○...Relatively good △...Slightly poor ×...Remarkably poor Table 1 '12゛# 10 550 5
□ ◎ 1 [Effects of the Invention] According to the present invention described above, an electrolytic chromate-treated steel sheet having excellent weldability can be easily manufactured, and the applications of this type of surface-treated steel sheet can be greatly expanded. There is an effect that can be done.

[Brief explanation of drawings]

FIG. 1 shows the relationship between the Sn adhesion amount and the contact resistance of a steel plate manufactured by the method of the present invention. Patent applicant Nippon Kokan Co., Ltd. Inventor Hiroshi Furuya Eido
Yutaka Watanabe Daido
Hiroki Iwasa, Patent Attorney
Sho Yoshihara Sando
Kiyoshi Takahashi Figure 1

Claims (1)

[Scope of Claims] Electrolytic chromate-treated steel sheets are temper-rolled at a reduction rate of 2 to 20% to form cracks in the chromate film, and then tin plated at a coating amount of 50 to 600 mg/m^2 per side. A method for manufacturing an electrolytic chromate-treated steel sheet for welding, characterized by subjecting it to.