JPS5852455A - Steel sheet for easy opening can top with superior can opening property - Google Patents

Abstract

PURPOSE:To obtain a steel sheet for an easy opening can top with a superior can opening property by dispersing a fine precipitate having a specified average grain size in a steel sheet. CONSTITUTION:A fine precipitate having 0.05-0.5mum average particle size is uniformly dispersed in a steel sheet in large quantities. The steel is rimmed steel, aluminum killed steel, silicon steel, titanium killed steel or other nonaging steel, and the desired precipitate is cementite. The effective carbon content of the steel is 0.06-0.25wt%, and the amount of precipitated cementite is adjusted to about 0.5-2.5wt%. Fine cementite is easily dispersed in large quantities by carrying out hot rolling at a low coiling temp. such as <= about 650 deg.C and annealing at a relatively low temp. such as <= about 680 deg.C in a short time. Thus, a steel sheet for an easy opening can top with a superior can opening property and high workability into the can top is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steel plate for easy-open can lids with excellent can opening properties.

In recent years, beer cans, carbonated beverage cans, juice cans, and various other food cans have been engraved with a notch (score) of an appropriate shape on the lid of the can, and a handle (tab) has been attached to a part of the score. Easy-open cans are widely used in which the consumer tears open the score by pulling on the tab without requiring any particular force. Aluminum has traditionally been widely used as a material for such easy-open cans because it has lower strength and is easier to open than steel, but in the can manufacturing industry, aluminum is widely used in can manufacturing. Since the cost is higher than that of steel, there is a strong desire to develop a steel plate for easy-open can lids that has the same opening performance as aluminum.

In general, the opening ability of cans depends on the thickness of the steel plate at the bottom of the score, which is scored into an inverted trapezoidal shape by press processing (remaining thickness of the score).For the same material, the thinner the remaining thickness of the score, the lower the opening force. If it is too large, cranks are likely to occur during score processing, and the score processing portion may be damaged during handling such as transportation. Therefore, there is a critical score residual thickness that can be processed without cranking, and the thicker the steel plate is, the higher the strength, and the more coarse inclusions there are, the larger the score residual thickness becomes. is 6 by adding a safety margin of about 10 to 20 μm to the critical score residual thickness.
The thickness is set to 0 to 90 μm.

As a measure to improve the openability of steel, P and Sn
Attempts have been made to add embrittling elements to the steel, such as embrittling elements, or to coarsen the cementite in the steel, but these methods deteriorate the ductility of the steel plate itself and make it difficult to attach the can lid to the can body. The workability of can lids, such as tightening or riveting to attach a tab to a part of the score, is significantly impaired.

On the other hand, if the embrittlement of the steel is suppressed in order to avoid this, the improvement in can openability is not sufficient.

In view of this situation, the present inventors conducted a detailed investigation on the can opening characteristics of steel. Compared to aluminum, the can opening force of steel is more dependent on the opening speed. It has been found that as the speed becomes relatively high (approximately 100 m5+/min), the difference in opening force with aluminum increases.

Based on this fact, the present inventors believe that in the case of gradual fracture such as tearing of a part of the score, if the smallest unit of the fracture surface, a dimple-like fracture surface, is made smaller, the energy generated per fracture surface unit will be reduced. Based on the assumption that the can opening force will be smaller even if the can opening speed is the same, we investigated the dispersion state of precipitates, which become the core of voids during can opening and directly affect the size of the fracture surface unit, and the fracture surface morphology. We have studied the relationship with can force in more detail and found that by controlling the dispersion state of precipitates, can opening performance can be improved without impairing can lid workability, which has led to the construction of the present invention.

That is, the present invention provides a steel plate for easy-open can lids with excellent can opening properties by uniformly dispersing a large amount of fine precipitates having an average particle size of 0.05 to 05 μm in steel.

Cementite, sulfide (MnS, Ti5), etc., which are not compatible with the base iron and are spherical and easily dispersed uniformly, are suitable as the precipitates that form the core of the voids.

If the average particle diameter of the precipitate exceeds 0.5 μm, the effect of reducing the can opening force will not be exhibited, or if it is too coarse, it will cause cranking during can lid processing or scoring processing. Moreover, if it is smaller than 0.05 μm, it will not contribute much to reducing the opening force because it will be consistent with the base metal.

The method for manufacturing a steel plate of the present invention will be described below.

There are no particular restrictions on the type of steel used in the present invention, including non-aging steels such as rimmed steel, aluminum guild steel, silicon killed steel, and titanium killed steel. As the precipitate, cementite is preferable because it does not increase production costs and the dispersion state can be easily controlled, and in this case, the carbon content as a steel component is 0.0.
6 to 0.25 wt% is effective; if it is less than 0.06 wt%, the amount of cementite precipitation is insufficient and the effect of reducing the can opening force is small; if it exceeds 0.25 wt%, the steel plate becomes hard and the can lid is damaged. Workability may be impaired. C content is 0.06
At ~0.25 wt%, the amount of cementite precipitation is approximately 0.
5 to 2.5 wt% (extraction residue analysis). Fine dispersion of a large amount of cementite can also be easily achieved by a continuous annealing method in which hot rolling is performed by winding at a low temperature of 650°C or less and annealing at a relatively low temperature of 680°C or less for a short time.

Although the can openability is significantly improved by such a large amount and fine dispersion of cementite, another effect is that solid solution C is formed in the cementite particles during cooling after annealing, as detailed in Japanese Patent Application No. 56-80947 by the present inventors. Since it becomes easier to capture, the amount of solid solute C in the base iron decreases, improving the ductility of the base iron and having a positive effect on the workability of can lids. This makes it possible to provide a steel plate for easy-open can lids that has both can opening properties and can lid processability, which are the aims of the present invention.

Hereinafter, the present invention will be explained in detail in Examples.

Example Four types of steel plates A, B, and C whose average particle diameter and precipitation amount of cementite were adjusted according to the treatment conditions shown in Table 1.
, D (tin coating amount #50, handling thickness O, 3 om) was subjected to actual lid processing (score shape is inverted trapezoid, score remaining thickness 80μ), and then can opening force was measured using a tensile tester, and the results are shown in Table 1. Got the results. As a result, compared to the steel plate A used for comparison (current steel plate for can lids, equivalent to T-4CA), B, C, and D in which the cementite of the present invention was made finer and dispersed in a larger amount
The i-plate exhibited excellent can-opening performance equivalent to or better than commercially available aluminum can lids with an opening force of 1.9 to 2.2 kg, and no problems were caused in the processability of can lids.

Claims (1)

[Scope of Claims] 1. A steel plate for easy-open can lids with excellent can opening properties, characterized in that fine precipitates having an average particle diameter of 0.05 to 0.5 μm are dispersed in the steel plate. 2. A steel plate for easy-open can lids with excellent can opening properties as claimed in claim 1, wherein the precipitates are mainly cementite. 3. A steel plate for easy-open can lids with excellent can opening properties as claimed in claim 1, wherein the steel has a carbon content of 0.06 to 0.25%.