JPS6056052A - Steel sheet for easy-to-open can having excellent opening property and production thereof - Google Patents

Abstract

PURPOSE:To obtain a tin plate for a can having small tensile force and excellent opening property in the stage of producing an easy-to-open can of the tin plate by using a stell sheet which contains a specific amt. of Al and contains extremely little oxygen as a blank material. CONSTITUTION:An inexpensive tin plate is used as a blank material in order to manufacture an easy-to-open can such as a beer can, carbonated drink can, fruit drink can or the like. The tin plate is manufactured by subjecting a thin steel sheet contg. <0.0035% C and 0.05-0.40% Mn, contg. 0.010-0.100% Al, contg. the oxygen limited to <=0.005% and contg., if necessary, <=0.05% in total of one or both of Nb and Ti to hot and cold rolling. The sheet is subjected to a recrystallization annealing treatment to have <=54 hardness (Hr 30T) and is then subjected to temper rolling at >5% draft. The rolled sheet is subjected to Sn plating, by which the steel sheet for the easy-to-open can having >=58 hardness and excellent opening property is thus produced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steel sheet having excellent can-opening properties as a material for easy-open cans, and a method for producing the same. Easy-open cans, which can be opened without the use of tools such as can openers and bottle openers, are commonly used.

Aluminum alloys are mainly used as materials for easy-open cans because of their ease of opening, except for cases where the contents pose a problem in terms of corrosion resistance.

However, if the content contains salt or electrolyte, and some aluminum alloys are used, a galvanic cell is formed, with the exposed part of the aluminum base serving as the anode and the pinhole part of the tin can body. (the cathode), electrochemical corrosion is accelerated, leading to pitting of the aluminum end in a short period of time.

As methods for preventing such problems, the following methods [F] to (2) can be considered.

■ Avoid using tin cans and aluminum end combinations for salty or electrolyte contents.

■ If the contents are as in (■) above, use an all-aluminum can.

(2) Even in the case of contents such as (2) above, a complete coating is applied to either the tin can body or the aluminum end to prevent the formation of galvanic cells.

However, method (2) has drawbacks such as the fact that aluminum is expensive, and method (2) it is difficult to completely prevent the aluminum substrate from being exposed at the rivet and score portions.

For this reason, efforts are currently being made to use tinplate as an easy-opening material, but tinplate generally has higher tensile strength and is said to have poorer opening performance than aluminum alloys.

Therefore, several techniques have been proposed for the purpose of manufacturing easy-open steel plates with excellent can opening properties. For example, there is a technique disclosed in Japanese Patent Publication No. 51-5888. According to the examples in the same publication, a of box annealing or oven annealing: 0.005 to 0.016%
, oxygen ? 0.014-0.026*, Si
: O, Oa upper and lower Mn': 0.25 to 0.88
1, the remainder being Fe and only unavoidable impurities, or a steel plate for easy-open cans further subjected to skin pass rolling at a rolling reduction of 8 to 15%.

Also, in Japanese Patent Application Laid-open No. 55-97428, C: 0.008
~0.0124, Si: 0.01~0.02%
, Mn: 0.28~81%, oxygen j O,009~
0.014%, A! :0,008~0.045 section 1/
, 0+Oxygen: 0.015 to 0.018 steel is continuously annealed and then skin bath rolled at a rolling reduction of 6 to 20 degrees, and a steel plate is disclosed as being suitable for easy-open cans.

Although these steels have the effect of improving can openability to some degree as shown in the detailed explanation column of each publication, they do not meet the recent demands for thinner and harder tinplates at all. There are drawbacks that cannot be overcome. That is, although there are few problems when used as a soft steel sheet for easy-open cans, problems arise particularly when manufacturing hard easy-open can materials with a heat treatment degree of 74 or higher using such steel sheets. This is because hard tinplate is inherently highly work hardened, and the score processing area is subjected to extremely strong processing.
In addition, strain age hardening occurs during baking after painting, so even if the hardness of the material is sufficiently low, the tensile strength of the scored part becomes locally extremely high.Therefore, the inventors of the present invention As a result of our efforts to develop steel sheets for easy-to-open cans that can meet the above requirements, we discovered that the strain age hardening described above is the biggest cause of poor can-opening performance. This succeeded in significantly reducing the force.

In other words, in general, the can opening force is (tensile strength of the llil plate, (2
) It is known that there is a strong correlation with elongation, and (3) score residual thickness. That is, in order to reduce the can opening force,
First of all, it is necessary to reduce the tensile strength of the steel plate. In this case, a particular problem is the tensile strength of the scored portion.

However, although the hardness of the steel plate has been adequately controlled in the past, no consideration has been given to the strength of the score-processed portion or the relationship between the elongation of that portion and the hardness of the steel plate.

As a result of various experiments, the inventors of the present invention have found that it is most important to suppress the solid solution 01Nil to a sufficiently low range in order not to increase the strength of the score processed part. . They also found that in order to reduce the score residual thickness, it is important to add an appropriate amount of AJ and to lower the oxygen content sufficiently.

The present invention has been completed based on these findings, and the gist of each invention is (1) Important i
0 at ts: 0.0085% or less, )(n + 0
．． 05-0.40%, Alt 0.010-0.10
Hardness (HRill OT)
A steel plate for easy-open cans with excellent can-opening properties, characterized in that the ratio is 58 or more, (2) O in weight%: 0.00851 or less, In +
0.05-0.40 4-5, AJ: 0.010
~0.100 1 warm; , @ element! 0.005
or below, and further contains one or two of Nb and Ti.
A steel plate for easy-open cans with excellent can-opening properties, characterized by containing 0.05% or less of seeds in total, the remainder consisting of Fe and unavoidable impurities, and having a hardness (HR80T) of 58 or more. ) O in terms of weight: 0.00851 or less, Ins 0.05-0.40, ill 0.0
10~o, ioo 4, Oxygen: 0.005% or less, the remainder consisting of Tel and unavoidable impurities is hot-rolled and cold-rolled, and then recrystallized to reduce the annealed hardness ( A steel plate for easy-open cans having excellent can-opening properties, characterized in that the hardness after plating is made to be 58 or more by temper rolling at a reduction rate of 5 minutes or more. (4) Weight: O: 0.003596 or less, In + 0.0
5~'0.40%, Mul+0.010~0.100
%, oxygen: o, ooi or less, further containing one or two of Wb and 1 in a total of 0.05% or less, and the balance consisting of Fe and unavoidable impurities. After rolling and cold rolling, it is annealed by recrystallization annealing.
The hardness (HR80T) of the can is 54 or less, and then the hardness after plating is made to be 58 or more by temper rolling with a rolling reduction of 5 or more. It is in the manufacturing method of steel plate for cans.

The present invention will be explained in detail below.

It is well known that steel generally tends to become softer as its carbon content decreases, and this softening tendency is mainly due to the coarsening of crystal grains as the carbon content decreases.

Many conventional soft steel sheets for easy-open cans utilize this crystal grain coarsening effect.

However, as a result of various experiments conducted by the present inventors, the strength of the score processed part does not only depend on the strength of the base plate, but also depends on the amount of distortion during score processing and the amount of hardening during subsequent baking painting. was found to be more important.

That is, as shown in FIG. 1, the amount of strain hardening during baking coating strongly depends on the amount of solid solution (0+N). Solid solution/element content is 0
．． When it becomes less than 0.00501, the amount of hardening decreases rapidly, and especially when it becomes less than 0.0085%, age hardening becomes almost negligible. In order to reduce the strength of the score processed part, it is very important to make this solid solution (0+N)i 0.00854 or less.

In order to satisfy these conditions, first, the amount of C must be reduced to 0.
．． Must be 0.085% or less. Furthermore, setting the amount of C to 0.0085 with a high yield has a remarkable effect in that the residual thickness of the score can be reduced.

In other words, when Cil is 0.005% or more, coarse plate-like carbides are precipitated at the grain boundaries, and when intense cold working such as scoring is performed, such carbides are A void is formed in the vicinity.

When the plate thickness becomes extremely thin as in the case of score processing, not only non-metallic inclusions such as oxides but also such coarse carbides cause the occurrence of bottle balls.

Therefore, setting the G-shape to 0.00351 or less is not only effective in softening the score processed part, but also very effective in reducing the remaining thickness of the score without generating pinholes. I found out that.

As a means for reducing the C cap to 0.00135% or less, a method of vacuum degassing treatment of molten steel is suitable.

Furthermore, for the purpose of reducing solid solution N, it is necessary to add an appropriate amount of AJ to fix N as A4N. However, if At contains a large amount, various alignments will occur, so A! The content is 0.01 to 0.10.

Furthermore, if necessary, it is also effective to add a small amount of Nb or Ti for the purpose of completely fixing solid solution G and N. However, if Nb and Ti exist in large amounts, they will significantly deteriorate the surface properties of the steel sheet, so the upper limit of the content should be set to Nb +
The total amount of Ti is 0°05%.

In addition, Nn is added to prevent hot embrittlement caused by S, which is present as an unavoidable impurity. However, if added in large amounts, hardening and deterioration of surface properties will occur, so the content should be in the range of 0.05 to 0.40%. Furthermore, in order to reduce the residual thickness of the score, it is important to reduce inclusions as much as possible. Therefore, the oxygen content is
Keep it below 0.005%.

If a steel with the above-mentioned components is hot-rolled and cold-rolled using conventional processes and annealed at a temperature higher than the recrystallization temperature, the as-annealed steel sheet hardness (HR80T) will be 54 or less. However, the stress-strain curve of the steel plate manufactured by this process is as shown in curve A in Figure 2, and the elongation is extremely large, resulting in a large amount of work required to open the can, that is, the opening force. Become. Furthermore, this steel sheet has a low tensile strength and cannot obtain sufficient hardness to manufacture hard tinplate of grade 74 or higher, which is in high demand.

In order to overcome these drawbacks, we have found that it is effective to subject the sheet after annealing to high-strength temper rolling and to simultaneously solve the problems of increasing hardness and decreasing elongation.

Ordinary hard tinplate, i.e. low carbon steel or N+
When a steel plate to which P, In, etc. are added is annealed by a simple heating-soaking-cooling cycle, the stress-strain curve is as shown in FIG. 2B. However, when a soft steel plate is hardened by skin pass rolling as in the present invention, the stress-strain curve becomes O
become that way.

When comparing the elongation of B and 0 at the same hardness level, C is overwhelmingly smaller. In order to sufficiently reduce the C elongation, skin pass rolling of coefficient 5 or higher is required.

When trying to manufacture hard tinplate with a hardness of 74 or more by such a method, the hardness of the as-annealed plate should be 54 or less,
Furthermore, they discovered that the hardness after plating could be increased to 58 or more by subjecting the material to temper rolling for 5 times or more.

As can be seen from the above description, the features of the present invention are that local hardening of the steel plate, especially the score-processed part thereof, is prevented by extremely reducing the C-shape, and carbide is completely eliminated. This aims to reduce the score residual thickness. Another object of the present invention is to produce hard tinplate that is hard and has low elongation by temper rolling a very soft steel plate.

As mentioned above, the manufacturing method of the present invention is effective for all factors such as the residual thickness of the score, the tensile strength of the score processed part, and the elongation of the steel sheet. Therefore, the obtained steel sheet has a synergistic effect of these factors. As a result, it exhibits extremely superior can opening performance compared to conventional materials.

Next, examples of the present invention will be shown.

(Example) Steel having the components shown in Table 1 was melted in a converter and continuously cast.

Note that IA-F has a reduced O content using a vacuum degassing device. These 6 steels are processed according to the normal process.
It was hot rolled at a finishing temperature of SOO°C and a winding temperature of 550°C to a thickness of 2.8 mm. After pickling, cold rolling to 0.28 mm,
After annealing at 700-750℃ for 20 seconds, 15℃/86
It was cooled at a cooling rate of C. Table 2 shows the hardness of the as-annealed plate, the hardness of the plated plate after skin pass reflow treatment, the remaining score thickness, and the openability.

From Table 2, steels A-D having the composition range of the present invention have a low hardness of 50 or less as annealed, and a hardness of 60 or less after skin bath rolling.
61 and T4, and both the pinhole generation critical score residual thickness and can opening force are sufficiently low.

On the other hand, #iE, a comparative example, has a low skin pass rolling rate and a large offsetting, resulting in poor can openability.Moreover, mF and G both have a large amount of O, have a large pinhole generation critical score residual thickness, and can open easily. When the force is high, the skin pass rolling rate is increased like steel F (e%)
However, it is not allowed in the direction in which the can is opened.

As is clear from the above description, according to the present invention, it is possible to manufacture and provide a hard steel plate for easy-open cans that has a small residual score thickness and is excellent in opening performance.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the solid solution ((3+N)j& in a steel plate and an age hardening needle, and FIG. 2 is a diagram showing the stress curve of the strain curve).

Claims (1)

[Claims] 1% by weight O: 0.00351 or less, In: 0
．． 05-0.404, At j O, 010-0.10
0%, oxygen: 0.005% or less, the remainder consists of Fe and inevitable impurities, hardness (HR80T) is 58
A steel plate for easy-open cans having excellent can opening properties, characterized by having the above characteristics. - Oj 0.0085 俤 or less in weight%, Mn + 0
．． 05-0.404, l: 0.010-0.100
%, oxygen = 0.0051 or less, further containing one or two of Nb and T1 in a total of 0.05% or less, the remainder consisting of Fe and unavoidable impurities, and hardness (
A steel plate for easy-open cans with excellent can opening properties, characterized by having a HR80T) of 58 or more. & Heavy Bes O: 0.00851 or less, In s
0.05-0.044, Aj: 0.0IQ-0.1
00%, oxygen: 0.0051 or less, with the remainder consisting of FB and unavoidable impurities. After hot rolling and cold rolling, the steel is recrystallized to an unannealed hardness (HR80).
An easy-to-open can with excellent opening properties, characterized in that the hardness after plating is made to be 58 or more by temper rolling at a rolling reduction of 5 factors or more. Method of manufacturing steel plates for industrial use. - On 0.00135% or less in weight ft%, Mn j
0.05~0.404, l+0.010~0.10
04. Oxygen: 0.005% or less, further containing one or two of Nb and T soil in total of 0.054% or less, and the balance consisting of Fe and unavoidable co-impurities,
After hot rolling and cold rolling, the hardness of the annealed ball (HR80T) is made 54 or less by recrystallization annealing, and then temper rolling is performed at a rolling reduction of 5 factors or more to make the hardness after plating 58. A method for producing a steel plate for easy-open cans having excellent can-opening properties.