JPS6296618A - Manufacture of top for easy open can - Google Patents

Abstract

PURPOSE:To manufacture a top made of steel sheet and superior in can openability, by recrystallization annealing cold rolled sheet made of low carbon steel, then working it to steel sheet material for top by skin pass, further score working so that the ratio of score residual thickness to steel sheet thickness is attained to a specified value at the titled manufacture. CONSTITUTION:Slab of low carbon Al killed steel contg. by weight 0.01-0.08% C, 0.05-0.50% Mn, 0.01-0.15% Al is hot rolled at finishing temp. of >=Ar3 transformation point of the steel to soft hot rolled plate having large grain diameters. The plate is cold rolled, then recrystallization annealed by continuous annealing, further the sheet is skin passed by 5-10% draft to steel sheet having <=0.21mm thickness. The sheet is score worked so that the ratio of score residual thickness to steel sheet thickness is attained to <=0.4 to manufacture top for easy open can superior in can openability.

Description

[Detailed Description of the Invention] (Industrial Application Field) Use of tinplate or tin-free steel ring Fi (simply referred to as tin plate original plate in this specification) for use in easy-open lids for food cans and beverage cans. Regarding suitability, this specification describes the results of research and development on a method for manufacturing an easy-to-open can lid that has both excellent can-opening properties and lid-making processability.

Up until now, aluminum and aluminum alloys have been mainly used as materials for the lids of easy-open cans due to their rust resistance and ease of opening.

However, in the case of contents containing salt or electrolyte, a galvanic cell (the exposed part of the aluminum base is the anode and the pinhole part of the tin can body is the cathode) is formed by using a part of the aluminum alloy, and the electrochemical Corrosion is accelerated, leading to holes in the aluminum lid in a short period of time. Therefore, in such a case, it is necessary to use an ultra-low carbon cold-rolled steel plate (hereinafter simply referred to as a thin steel plate), typically tinplate or tin-free steel, as the material for the lid.

On the other hand, from the viewpoint of recovery in response to strong social demands regarding the disposal of empty cans, it is desirable that the can stock be made of a single material.

From this point of view, it is expected that demand for easy-open can lids (hereinafter abbreviated as EOE) made of thin steel sheets will increase in the future.

(Prior art) Conventional EOE scraping is a continuously annealed material generally called 74-CA, which has a tempering degree of T4 in accordance with JIS G-3303, and has a product thickness of 0.22 to 0.26n+. steel plates have been used. However, in the case of this tin EOE, the opening performance is far inferior to that of the aluminum EOE.

Therefore, as a method for improving the can-opening property, a method of coarsening the precipitated carbides and increasing the starting points of cracks (Japanese Patent Application Laid-Open No. 55-62
Lord No. 142! 1) A method in which fine cementite particles and martensite particles are uniformly dispersed in a base steel sheet using a high carbon material to promote void nucleation when the can is opened (Japanese Patent Application Laid-Open No. 1983-1982).
-24328) has been proposed.

(Problems to be Solved by the Invention) On the other hand, the above-mentioned measures to improve can openability may lead to other problems in riveting workability, impact resistance, etc., such as detachment of the tab or problems during transportation of the product. Therefore, it is an object of the present invention to improve both the lid-making properties including riveting and the can-opening properties.

(Means for Solving the Problems) The inventors repeatedly conducted various experiments to improve the can opening performance of EOE.
It means a reduction in can opening resistance when a tensile force is applied to a tap caulked to the E score processing part, that is, a reduction in pop value.

Based on the above experimental results, we found that: ■ Openability can be improved by reducing the plate thickness and the remaining score thickness; ■ If the plate thickness is made thinner, there will be problems with riveting workability unless the particle size of the base material is increased. They found that it is necessary to solve this problem metallurgically, and recognized that the above object can be advantageously achieved by following the manufacturing method described below.

That is, in this invention, C: 0.01 to 0.08 wt%
, Mn: 0.05~0.50wt%, A1: 0.01~
A steel slab containing 0.15 wt%, balance Fe and unavoidable impurities was hot rolled at a finishing temperature below the Ar3 transformation point, then cold rolled, recrystallized by continuous annealing, and then Using a thin steel plate with a thickness of less than 0.21 m1 obtained by skin bathing at a rolling reduction rate of 5 to 10%, the score residual thickness /! This is a method for manufacturing an easy-open can lid that performs score processing such that the ratio of 12I plate thickness is 0.4 or less.

(Function) Figure 1 shows the relationship between the EOE Bo-Nobu value and the steel plate thickness.
It can be seen that the pop value improves significantly as the steel plate thickness decreases.

By the way, the pop value is AI! ! ! ! EOE pop value (1
, 7 kg), the steel plate thickness needs to be less than 0.21 mm from FIG. 1.

Further, FIG. 2 shows the relationship between the EOE pop value and the ratio of score residual thickness/steel plate thickness, which were manufactured using a thin steel plate having a thickness of 0.20±0.01 mm. From FIG. 2, it can be seen that in order to make the pop value 1.7 kg or less, the ratio of score residual thickness/steel plate thickness needs to be 0.4 or less.

As mentioned above, by making the steel plate thickness less than 0.21 mm and regulating the ratio of score residual thickness / I plate thickness to 0.4 or less,
^l EO made by Steel with improved can opening performance on par with EOE made by Steel
E can be obtained, but on the other hand, as the steel plate thickness decreases, problems tend to occur in riveting workability. Since this problem can be improved by increasing the crystal grain size of the tinplate original plate, low C-1 killed steel, which will be described below, is used as the material.

As the low C-Al killed steel, a composition system generally used for tinplate and tin-free steel plates is used. This is also beneficial from the standpoint of the versatility of the slab. The component composition consists of unavoidable impurities such as P e s and S in addition to each component of C+ Mn and Al, and the reasons for limiting each component are as follows.

C: 0.01 to 0.08 wt% If C exceeds 0.08 wt%, it becomes impossible to apply a skin pass reduction rate sufficient to obtain a desired degree of tempering.

Furthermore, since an increase in carbide would raise concerns about the impact resistance of the scored portion, the C content was limited to 0.08 wt% or less. The lower limit was set at an industrially producible level of 0.01%.

Mn: 0.05 to 0.5wt% Mn needs to be contained at 0.05wt% or more to prevent hot embrittlement caused by S, which is an inevitable impurity, but it also prevents the strength from increasing too much. Therefore, the upper limit is 0.5w
It was set as t%.

A1: 0.01 to 0.15wt% AI needs to be contained at a minimum of 0.01%, which is necessary for deoxidation, to prevent the occurrence of blowholes during continuous casting. Since the addition of C is economically disadvantageous, the upper limit was set at 0.15%.

By hot rolling the low C-Al killed steel having the above-mentioned composition at a finishing temperature below the Ar3 transformation point, a soft hot-rolled base plate with a large grain size can be obtained.

After cold rolling this mother plate, it is recrystallized by continuous annealing,
Connect to skin pass process. The reason why continuous annealing is used here is to ensure uniformity of the material and realize highly efficient production.

The hardness obtained after continuous annealing is equivalent to T2 to T3 in terms of the degree of tempering. The tempering degree of the original plate used as EOE is generally T3.
~T5, and in the skin bath process, 5 is used to match the hardness.
~10% reduction is required. In addition, in this invention, the skin pass rolling reduction rate is specified to 5 to 10%, but the reason for this is not simply to match the hardness, but by applying a rolling reduction of 5% or more, the strain is reduced to the vicinity of the center of the steel plate and a uniform material quality is obtained. and to prevent stretcher strain.

On the other hand, if the rolling reduction exceeds 10%, the degree of heat refining exceeds T5 and impedes riveting workability, so 10% was set as the upper limit of the rolling reduction.

(Example) Steel with the composition shown in Table 1 tapped in a 230 ton bottom blowing converter was made into a 260 mm thick slab by continuous casting, and then hot rolled at temperatures of levels A and B2 shown in Table 2. .3 thick hot coil. These hot coils were cold-rolled, then continuously annealed at 700°C x 4O5, and subjected to skin bath treatments at various rolling reduction ratios to produce 8 tin blanks with a thickness of 0.20 mm.

Table 1 (WT%) Table 2 After tin-plating the obtained tin plate, an EOE with a diameter of 211 was manufactured, and the opening force and workability were evaluated. The results are shown in Table 3 along with the skin pass reduction rate. .

From Table 3, it is clear that Sample 2.3, which is a material compatible with the present invention, exhibits a small pop value and good revent processability, and is able to achieve both can opening and lid forming properties.

(Effects of the Invention) According to the present invention, it is possible to provide an EOE that satisfies the required performance of can opening and lid forming properties.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between steel plate thickness and pop value, and Figure 2 is a graph showing the relationship between the ratio of score residual thickness/steel plate thickness and pump value. Copper R thickness (thickness four

Claims (1)

[Claims] 1. C: 0.01 to 0.08 wt%, Mn: 0.05 to 0.50 wt%, Al: 0.01 to 0.15 wt%, balance containing Fe and inevitable impurities. steel slab,
After hot rolling at a finishing temperature of Ar_3 transformation point or lower, then cold rolling, recrystallization annealing is performed by continuous annealing,
After that, the plate thickness obtained by skin pass with a rolling reduction of 5 to 10% is 0.
．． A method for producing an easy-open can lid, characterized in that a thin steel plate of less than 21 mm is subjected to score processing such that the ratio of score residual thickness/steel plate thickness is 0.4 or less.