JP2528166B2 - Sn-plated ultra-thin steel sheet for cans with excellent flange formability and weldability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a tin-plated ultra-thin steel sheet having a thickness of 0.12 to 0.18 mm for food cans and beverage cans to be inlaid mainly by seam welding, and its flange formability and welding. It has improved sex.

<Prior Art> In recent years, a seam welding method has been widely used as a joining method for a can body instead of a conventional solder joining method. The seam welding method is
Compared with conventional solder cans and adhesive cans, the wrap portion is thinner, so that the winding tightness is better and the side seam portions are stronger.

As a material for such a welding can, a plate thickness produced by a so-called SR method in which a low C material having a C content of 0.03 to 0.06% has been continuously annealed and a skin pass finish having a reduction rate of 2% or less has been performed. 0.
Steel plate of 20 mm or more is used.

However, in the field of cans, especially beverage cans, there are many low-priced competing materials such as aluminum, plastics, paper, etc.
Sn-plated steel sheet is in a costly position. Therefore, recently, a welding can using an ultra-thin steel plate having a plate thickness of 0.12 to 0.18 mm which has been subjected to secondary rolling (DCR method) at a rolling reduction of 5 to 30% after annealing has been attempted.

However, these ultra-thin steel sheets are combined with the problem that the heat-affected zone during welding of the side seams tends to crack during flange processing for attaching the canopy or bottom lid to the can body after the side seams. This caused a problem that the welding proper current range (ACR) became narrow.

Flange cracking occurs because the material is hardened by secondary cold rolling and the hardness of the side seam portion is further increased due to the heat effect during welding.

Therefore, until now, welding cans using DCR materials have used box-annealed materials with less flange cracking than continuous annealed materials. It is considered that the box annealed material has a large number of crystal grains of the steel sheet and a small increase in hardness in the heat-affected zone during welding, so that the occurrence of flange cracking is small. However, box annealing is much longer in annealing time than continuous annealing and not only has poor productivity, but is also inferior in plate material and flatness uniformity.

In addition, the seam welding method uses the heat generated by the electrical resistance of the steel sheets to melt and join the steel sheets.Therefore, if the sheet thickness is thin, the inside of the steel sheets will melt after the joining of the steel sheets begins to cause a splash. The current range to reach the limit is reduced. That is, in other words, the proper welding current range is narrowed, and welding becomes difficult.

On the other hand, until now, C was 0.00
An aluminum-killed steel sheet with a Hb content reduced to 4% or less and a trace amount of Hb has been proposed in Japanese Patent Laid-Open No. 58-197224. No Sn-plated steel sheet with good properties was obtained.

<Problems to be Solved by the Invention> The present invention has a low cost that can withstand other can materials such as aluminum, and has excellent flange formability and weldability.
It provides a Sn-plated ultra-thin steel sheet.

<Means for Solving the Problems> In the present invention, C: 0.004% or less by weight%, Si: 0.04% or less, M
n: 0.05 to 0.3%, S: 0.02% or less, P: 0.02% or less, Al: 0.02 to
0.15%, N: 0.004% or less, Nb: 0.01% or less, the balance being substantially Fe, with a sheet thickness of 0.12 to 0.18 mm. The basis weight of the can inner surface equivalent side is the can outer surface equivalent side. Sn greater than quantity
It has a plating layer, and the Sn basis weight on the side corresponding to the inner surface of the can is preferably
1.0 to 5.5 g / m ² , Sn basis weight on the outside of the can is 0.5 to 2.8 g / m ²
It is a Sn-plated ultra-thin steel sheet for cans having excellent flange formability and weldability.

<Operation> First, the reasons for limiting the components of the steel sheet of the present invention will be described.

The C content is 0.004% or less in order to improve the elongation of the steel sheet and improve the flange formability. The present inventors have used C: 0.03 which has been used as a steel sheet for cans so far.
It was found that even if it is an ultra-thin steel sheet, the flange formability becomes good by setting a fairly small amount in the range of 0.004% or less compared to ~ 0.06%.

For Si, Mn, S, N and P, the presence of a large amount of these elements suppresses grain growth during continuous annealing, not only hardening the plate but also impairing the corrosion resistance of tinplate. . Therefore, the smaller the better, Si: 0.04% or less, Mn: 0.3%
Below, S: 0.02% or less, N: 0.004% or less, P: 0.02% or less. However, Mn is S that causes embrittlement during hot rolling.
Is fixed as MnS, it is necessary to contain 0.05% or more.

Al needs to be added in an appropriate amount in order to fix N as AlN and reduce the solid solution N, but addition of a large amount increases the cost, so Al is made 0.02% to 0.15%.

Furthermore, the addition of a trace amount of Nb completely fixes the solid solution C and N,
The in-plane anisotropy of the r value is reduced and the workability is improved. However, addition of a large amount increases the manufacturing cost, so the content is limited to 0.01% or less.

In the present invention, so-called differential thickness plating is performed in which both sides of the steel sheet are plated with Sn so that the amount of Sn basis weight on the side corresponding to the inner surface of the can is greater than that on the side corresponding to the outer surface of the can. The reason for doing this is that the flange workability and weldability are greatly improved when the can body is configured with the thicker side as the inner surface of the can.

Of the two electrodes that sandwich the weld during seam welding, the electrode on the inner surface of the can has a smaller electrode wheel diameter and a smaller cooling capacity for heat generated by resistance than the outer surface of the can, so the inner surface of the lap is not affected by heat. Receive big. The inventors of the present invention have found that a difference in hardness between the inner surface side and the outer surface side of the lap portion due to the difference in thermal influence causes distortion during flange processing, which is a factor of flange cracking. Therefore, by increasing the amount of Sn weight on the inner surface of the can that contacts the electrode with a smaller diameter than on the outer surface and reducing the resistance heat generation between the electrode and the plate, the difference in the thermal effect between the inner surface and the outer surface of the wrap part is reduced. Can work without cracks.

When the plate thickness is extremely thin, about 0.12 to 0.18 mm, splashing tends to occur as described above, making welding difficult.
Since this splash is often generated on the inner surface of the can, by increasing the Sn areal weight on the inner surface of the can, resistance heating between the inner plate and the electrode can be reduced, the occurrence of splash can be suppressed, and the proper welding current range can be widened. And commercial production is now possible.

The Sn plating amount is preferably 0.5 to 5.5 g / m ² . If it is less than 0.5 g / m ² , not only is the corrosion resistance poor, but
The amount of Sn metal remaining after painting and baking is small, and the weldability is poor. ^{On the other hand} , if it exceeds 5.5 g / m ² , the manufacturing cost becomes high, and the reduction in cost, which is the aim of the present invention, is impaired.

Further, it is more preferable from the viewpoint of flanging workability and weldability that the Sn areal weight of the inner surface of the can is twice or more than that of the outer surface of the can.

Preferably, the amount of Sn on the inner surface of the can is 1.0 to 5.5 g / m ² , the amount of Sn on the outer surface of the can.
The amount is 0.5-2.8 g / m ² .

As described above, the present invention is very advantageous in terms of manufacturing cost,
It is possible to obtain a Sn-plated ultra-thin steel sheet having excellent corrosion resistance, weldability, and flange formability.

<Example> Next, the present invention will be specifically described based on Examples and Comparative Examples.

Other than C and Nb shown in Table 1, the components of aluminum-killed steel generally used as steel plates for cans, that is, Si: 0.04%
Or less, Mn: 0.05 to 0.3%, S: 0.02% or less, P: 0.02% or less, Al:
0.02 to 0.15%, N: 0.004% or less adjusted plate thickness 0.12 to 0.18
Examples 1 to 4 and Comparative Examples 1 to 5 in which a continuous annealing DCR material of mm, degreasing, pickling, Sn plating in a halogen bath, reflow treatment, and then chromate treatment were performed. Example 5 produced by the above method except that Sn-plated ultra-thin steel sheet was further plated with 0.07 g / m ² of Ni before continuous annealing, which is widely used as a thin-grained tint, and other than that.
7, Comparative Examples 6 to 7 Corresponding Sn-plated ultra-thin steel sheets were obtained.

The Sn-plated ultra-thin steel sheet was tested for weldability, flange formability, and corrosion resistance according to the following procedures.

Weldability A copper wire of about 1.5 mmφ is used as a welding electrode, and while moving this, the test material specimen is stacked under constant pressure, and electric resistance welding is performed at a welding speed of 55 m / min. The proper welding current range was determined under the condition that the strength was sufficient and no splash was generated.

Flange machinability Flange machinability of the above-mentioned welded can was performed, and the flange machinability was evaluated as follows based on the incidence of flange cracking.

Occurrence rate of flange cracks (ppm) Evaluation 0 ○ 1-100 △ 100 or more × Corrosion resistance (IEV) Indicates the degree of iron exposure, the inner surface of the can, in a mixed solution of sodium carbonate and sodium hydrogen carbonate,
Constant potential electrolysis was performed and the current value at that time was measured. The higher the value, the greater the iron exposure.

(ATC) The ATC value after air-baking at 210 ° C. for 20 minutes was measured on the inner surface of the can.

(Rust resistance test) The surface of the outer surface of the can was observed with a dry-wet cycle tester after 1 week for rust generation, and judged as follows.

Number of rust occurrences (in 100 cm ² ) Evaluation 0 ◎ 1-10 ○ 11-50 △ 51 or more × In Comparative Example 1, since the amount of Sn on the inner surface side is small, there is no proper welding current range and the flange formability is not good.

In Comparative Example 2, the C content in the steel is large and Nb is not added, so that the flange formability is poor.

Comparative Example 3 is inferior in flange formability because Nb is not added to the steel.

Comparative Example 4 has a large amount of C in the steel, and thus has poor flange formability.

In Comparative Example 5, the flange formability is good, but the Sn plating amount is small, so there is no proper welding current range and the corrosion resistance is poor.

In Comparative Example 6, the amount of C in the steel is large and the amount of Sn on the inner surface of the can is small, so that there is no proper welding current range and the flange formability is poor.

In Comparative Example 7, since the Sn adhesion amount on the inner surface side of the can was small, there was no proper welding current range and the flange formability was slightly inferior.

In Examples 1 to 7 satisfying the conditions of the present invention, there was a sufficient welding proper current range and no flange cracking occurred. In particular, the amount of Sn plating on the inner surface of the can is 2 times the amount of Sn plating on the outer surface of the can.
In Examples 1 to 3 and 5 to 7 in which the double or more times were set, a wide welding proper current range was obtained even with the same total Sn amount on the front and back sides. In particular, Example 5
Since Nos. 7 to 7 have been subjected to the Ni diffusion plating treatment, the proper welding current range is wider and the Sn amount can be further saved. It is considered that this is because the amount of free metal Sn increases due to the Ni diffusion treatment.

In addition, in Examples 1 to 7, since the amount of C in steel is small, there are few pinholes for plating, and
Corrosion resistance is also superior to Sn-plated steel sheet.

<Effects of the Invention> According to the present invention, an ultra-thin steel sheet having a plate thickness of 0.12 to 0.18 mm, a Sn-plated ultra-thin steel sheet for welding cans having excellent flange formability and weldability can be obtained at low cost, and can be saved. It greatly contributes to resource and energy saving, and its economic value is extremely high.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Mochizuki 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Koji Yamato 1 Kawasaki-cho, Chiba-shi Kawasaki Steel Co., Ltd. Corporate Technology Research Division (56) Reference JP-A-57-35693 (JP, A) JP-A-61-270389 (JP, A) JP-A-56-51532 (JP, A)

Claims (2)

(57) [Claims] 1. C: 0.004% or less by weight%, Si: 0.04% or less, M
n: 0.05 to 0.3%, S: 0.02% or less, P: 0.02% or less, Al: 0.02 to
0.15%, N: 0.004% or less, Nb: 0.01% or less, the balance being substantially Fe, with a sheet thickness of 0.12 to 0.18 mm. The basis weight of the can inner surface equivalent side is the can outer surface equivalent side. Sn greater than quantity
A tin-plated ultra-thin steel sheet for cans, which has excellent flange formability and weldability and is characterized by having a plating layer. 2. The weight of Sn on the side corresponding to the inner surface of the can is 1.0 to 5.5 g / m ² ,
The tin-plated ultra-thin steel sheet for cans having excellent flange formability and weldability according to claim 1, characterized in that the basis weight of Sn on the outer surface side of the can is 0.5 to 2.8 g / m ² .