JPS60121224A - Production of steel sheet for easy-to-open can having excellent openability - Google Patents

Abstract

PURPOSE:To obtain a steel sheet for a titled can having excellent openability by regulating the secondary cold rolling rate after hot rolling, primary cold rolling and annealing which are intermediate stages for producing a steel sheet for an ordinary can in a specific range from the relation among the hardness, content of C and cleanliness after annealing. CONSTITUTION:The above-described secondary cold rolling rate R is regulated by the equation and is made into the range of R<45 then hot rolling, primary cold rolling, annealing and secondary cold rolling which are intermediate stages for the steel sheet for the can are successively accomplished. Hardness H in this case varies with an annealing method (box annealing, continuous annealing, etc.), annealing conditions (temp. and heating and cooling conditions) and steel components and is generally in a 40-65 range in HR30T hardness. The content of C can be adjusted in a <=1,300ppm range with the steel plate for the can according to the decarburized state of the molten steel or the presence of absence of decarburization annealing in the intermediate stage. The resulting steel sheet for the easy-to-open can has good openability even if the residual thickness of a score is the same and further the reduction in the residual thickness of the score is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a steel plate for easy-open cans having excellent can opening properties. Hardness after annealing following hot rolling and primary cold rolling in the manufacturing process of steel sheets for cans (
HR30T), cleanliness (dsox4oo%...J
According to IS GO555), the rolling ratio between the secondary seats after annealing is determined in relation to the carbon content (ppm), and steel sheets for easy-open cans with good can opening properties are manufactured. Recently, various food cans, etc. have been fitted with appropriately shaped notches (
Easy-open cans are widely used, in which a handle (tab) is attached to a part of the can lid with the score engraved on it, and the lid can be opened without using a can opener by pulling the tab. There is. As the material for these easy-open cans, steel plates are used for contents that have problems with corrosion resistance, but aluminum is generally used mainly because of its good can-openability. However, aluminum is considerably more expensive than steel plate in terms of cost, and there is a strong need to develop an easy-open lid made of steel plate that is inexpensive and easy to open as an alternative to aluminum (
desired. The following two methods can be considered to improve the ease of opening the Easy Open H, that is, the quick opening performance. One method is to reduce the remaining thickness after score processing, that is, the remaining score thickness, and the other method is to reduce the can opening force without reducing the remaining score thickness. In the method of thinning the remaining score thickness, it is not possible to make the remaining score thickness sufficiently thin due to constraints such as cracks in the score part, damage when subjected to impact such as falling, and processing accuracy of the press that processes the score. . Furthermore, even with methods of improving can opening force without changing the remaining score thickness, the reality is that sufficient improvement has not been achieved even if various adjustments are made to the material properties of the lid shrine.

Based on the above circumstances, the present invention has been developed based on the idea that if the above two methods can be implemented simultaneously, a large improvement in can openability should be obtained. We have discovered a method for producing a steel plate for easy-open cans that has good can-opening properties and can also reduce the remaining thickness of the score.

The contents of the present invention will be explained in detail below.

The present invention aims at determining the rolling rate between the secondary seats of hot rolling, primary rolling, annealing, and secondary cold rolling, which are intermediate steps in the conventional manufacturing process of steel sheets for cans, the hardness after annealing, and the carbon content. , in relation to cleanliness, 100-0.08X (C+1,0OOXP) -〇, 8
XH>R>20...Formula (1) and 45>R...
By satisfying the range of formula (2), a steel plate for easy-to-open cans with good can opening properties can be manufactured. Note (1)
Equation (2) is an experimental equation, and R is the rolling ratio between the secondary seats (%
), C is carbon ffi (1)l)Ill).

H is I (R30'r hardness, P is cleanliness (d6ox4oo
%). Hardness is determined by annealing method (box annealing, continuous annealing, etc.).

The annealing conditions (/MT'J-, heating and cooling conditions) vary depending on the steel composition, and generally J (R30T hardness is in the range of 40 to 65.The carbon content is determined by the decarburization state during molten steel or the intermediate process) Depending on the presence or absence of decarburization annealing, the content of steel sheets for cans can be adjusted within the range of 1.300 ppm (0.13%) or less.Cleanliness is determined by the method of deoxidizing molten steel.

Although it varies depending on the steel composition, it is generally 0.001 to .08%. The basis for determining the rolling rate between the secondary seats as described above is as follows. First, the relationship between the thickness of the lid material, yield stress, and can openability will be explained.

The thickness of the lid material is determined by the yield strength of the lid ((square of the lid thickness) x
(It is determined by the yield stress of the lid shrine, and the lid deforms plastically if internal and external pressure acts on it at tL above the yield strength), the harder the lid is, the thinner the comb (ξ) is.

However, since the amount of elastic deformation is proportional to (the cube of the plate thickness),
Even if the yield strength is the same, a hard plate with a thinner thickness will have a larger amount of elastic deformation than a softer plate with a thicker thickness. In addition, the force acting on the lid is large during heating for the purpose of sterilization, and at that time, the strength that the lid does not deform plastically, that is, the plate thickness of the lid material and the yield stress are determined based on the yield strength of the lid. is often determined.

Here, we machined a soft, thick plate with the same yield strength and a hard, thin plate to the same score residual thickness, and compared their opening forces. The result was that the can opening force was lower. This is an open can,
That is, in order to break the score part, a certain amount of deformation is also required around the score part, but the harder and thinner the material, the better because the deformation amount can be obtained with smaller force.

Therefore, if the remaining thickness of the score can be the same, the harder and thinner the material is, the more advantageous it will be in opening the can. Next, the critical score residual thickness (minimum score residual thickness that can be processed without causing cracks in the score portion) will be explained. The limit score residual thickness of a soft and thick plate with the same yield strength, a thin plate made hard by rolling between secondary seats, and a thin plate made hard by heat treatment, adjustment of steel composition, etc. compared. The critical score residual thickness of soft and thick plates and thin plates made hard by secondary seat rolling is about the same and small, and cracks do not occur even when the thickness is thinner. However, the limit score residual thickness of a thin plate made hard by adjusting the heat treatment 2 steel components etc. is higher.The reason for this is that a soft one has a higher score processing degree ((lid material plate thickness - Score residual thickness)/M base plate thickness,
One reason for this is that if the score is to be processed to the same scale and score remaining thickness without generating cracks, the degree of score processing will be smaller for sheets with a thinner cumulative thickness. However, the reason why the critical score residual thickness becomes small is that the crystal structure after rolling between the secondary seats becomes elongated elongated grains (rolling texture) parallel to the sheet surface. It is considered suitable for reducing the critical score residual thickness. Next, the strength that the score part can withstand without being damaged when receiving an impact such as a fall (hereinafter referred to as drop F strength) will be explained. Naturally, if the remaining score thickness is reduced, the drop strength will be reduced, but if the remaining score thickness is constant, a hard lid material with a thin plate thickness will have a higher strength than a lid material with a soft texture and floating.

This is thought to be because a hard lid with a thinner plate deforms elastically and absorbs the impact when the lid squeaks or falls as a whole, reducing stress concentration on the score section.

The opening force required for these easy open ends,
Numerous tests on critical Skoy residual thickness and drop strength have shown that when the yield strength of the lid is the same, a thinner plate made hard by secondary seat rolling is extremely superior as a steel plate for easy-open cans. I found it. Here, when obtaining a certain hardness by rolling between secondary seats, the softer the
The rolling rate increases, and the harder the material, the lower the rolling rate.

As the rolling ratio increases, the crystal grains become more elongated in parallel to the plate surface. The critical score residual thickness is smaller for a soft material that is rolled between the secondary seats at a higher rolling rate than for one that is rolled between the secondary seats at a higher rolling rate. In addition, the amount of carbon and the amount of nonmetallic inclusions also affect the critical score residual thickness. As a result of the test, the carbon content was ppH1.

Code C1 The amount of nonmetallic inclusions is the cleanliness (d60X40...
%) When expressed with the symbol P, its influence on the remaining marginal score Jy can be summarized as (C+1,000 XP). As the value of (C1-1, ,000X P ) increases, the critical score residual thickness increases, but (C+1,000X
It is preferable to determine the value of P) by considering the hardness before rolling between the secondary seats, and for products whose hardness is hard before rolling between the secondary seats, it is necessary to keep (C+1,000xP) small. However, for soft ones, the critical score residual thickness is improved based on the greater elongation of crystal grains by secondary cold rolling, so (C + 1,000xP)
Consideration to keep the size small is not required in the case of hard objects. In those whose hardness becomes soft after annealing (C
+1,000 xP) more than necessary will unnecessarily increase the cost of the material. Limit score residual thickness, hardness after annealing, and carbon content.

The relationship between the cleanliness and the rolling rate between the secondary seats is as described above, but the upper limit of the rolling rate between the secondary seats is determined from the openability, which also takes into account the critical score residual thickness. As the rolling rate increases, the degree of hardening of the material decreases, and even if the rolling rate is thicker than the secondary rolling rate derived from equation (1), the material plate thickness decreases due to the hardening of the material, and the crystal grains decrease. In addition to the effect of improving the critical score residual thickness due to rolling, the material becomes extremely brittle, the critical score residual thickness increases, and the opening force increases.Also, the secondary rolling ratio increases to 45% or more. For example, the negative effect of material embrittlement is greater (the critical score residual thickness increases,
Can opening force increases. Therefore, the value on the left side of equation (1) is 45
As can be seen from the above, even if attempts are made to reduce the value of (c+1000 do not have. For the above reasons, the upper limit of the rolling rate between secondary seats was determined. In addition, the lower limit of the rolling ratio between the secondary seats was set at 20% because if it is less than 20%, hardening will not be sufficient and thinning of the plate will not be achieved. This is because it cannot be obtained. Here, the hardness after annealing is determined by the steel composition, heat treatment method, etc., and these selections are made in consideration of economic efficiency, corrosivity of the filling contents, etc. Further, the rolling rate between the secondary seats after annealing is selected depending on the type of lid and the type of scoring process. The steel sheet produced in this manner is then subjected to pretreatment such as degreasing and pickling, and then subjected to tin plating, chromium plating, phosphate treatment, and other chemical conversion treatments, and is used as a steel sheet for easy-open cans.

Examples of the present invention will be described below.

Table 1 The steels shown in Table 1 were melted in a converter. Steel A is decarburized and deoxidized to the components listed in Table 1 during molten steel using a vacuum descaling device, and then ingot-formed, hot-rolled, and processed according to the normal stripping process.
After inter-rolling, box annealing or continuous annealing was performed. Steel B was made by ordinary ingot making but had a low carbon content, and was subjected to box annealing or continuous annealing after ingot formation, hot rolling, and rolling between primary seats. Steel C is produced by ordinary melting.
The steel sheet had an average carbon content level for a can steel sheet, and was subjected to box annealing or continuous annealing after ingot formation, hot rolling, and primary seat rolling. The steel is the same as Steel C up to the hot rolling process, but those that undergo continuous annealing after rolling between the first seats are decarburized before the first cold rolling, and those that are not continuously annealed are subjected to continuous annealing between the first seats. After rolling, box-type decarburization annealing was performed. Steel E has the same manufacturing process as steel, but decarburization was intentionally stopped early to adjust the carbon level. The values in the upper row of the C amount after decarburization of #1D and steel E are the values decarburized after primary rolling, and the values in the lower row () are the values decarburized before cold rolling. . If the hardness after rolling between the primary seats is I (R30T and 40 to 55), box-type annealing or box-type decarburization annealing is used. If the hardness after annealing is 1R301 and 55 to 65, continuous annealing is used. It was done by ((, the yield strength is the same ((plate 1', 7 2 east) x (yield stress of material)
- A predetermined plate thickness and hardness were obtained by rolling between the secondary seats to a predetermined thickness and hardness. After rolling between the secondary seats, wipe
Perform tin plating in Ferosuf/bath, then add lid-1
[was done.

The lid was scored with a diameter of 58 mm for a fully open can. The riveting process for removing the tab for opening a can is difficult because there are many types of plate thicknesses for lids and A materials, so it is difficult to prepare a mold according to the plate thickness, and it is difficult to prepare a mold according to the thickness of the plate. I soldered a tin tab in place to replace the rivet. The quality of can openability is determined by the limit score remaining thickness of each material + 1
Evaluation was made based on the maximum tearing force following the initial can opening force at the score remaining thickness of 07) m, and based on the values of temper 25 (I (R30T52-58) and plate thickness 023 currently used for fully open cans). Figure 1 shows the results.

It is shown in Figure 2. Figure 1 shows the hardness (f-1 nao T
) is 48-53, and Fig. 2 shows hardness σ (R30T) of 58-6 before rolling by continuous annealing.
4, the relationship between (C+1,0OOXP), rolling ratio between secondary seats, and can openability is shown. Compared to the standard value (temper 25, plate thickness 0.23 can opening force), those with an improvement of only 75% are △, those with an improvement of 75 to 15% are ○, and any further improvement Those obtained are indicated by ◎. The range of the present invention surrounded by the broken line in the figure, that is, the hard and thin steel plate manufactured within the range where the rolling ratio between the secondary seats satisfies equations (1) and (2) (however, the yield strength is No change)
It can be seen that the can-opening property was improved by 75% or more, and it is excellent as a material for easy-open cans. Although the example shows the case of tinplate, the surface treatment is limited to tinplate, and tin-free steel or other chemically treated steel sheets may also be used. Furthermore, the tabs were attached by soldering for convenience, but this is not intended to limit the method of attaching the tabs.

[Brief explanation of the drawing]

Although the hardness (HR30T) after annealing is 48 to 53, Fig. 1 shows the relationship between (carbon content + 1,000 x cleanliness), rolling rate between secondary seats and can openability, and Fig. 2 shows Although the hardness (HR30T) after annealing is 58 to 64, the relationship between (carbon content + i, ooo x cleanliness), rolling rate between secondary seats and can openability is shown.

Claims (1)

[Claims] Hot rolling, which is an intermediate process in the normal manufacturing process of steel sheets for cans, 1
The relationship between the secondary seating rolling rate of secondary seating rolling, annealing, and secondary cold rolling is the hardness, carbon content, and cleanliness after annealing. R: Secondary seating rolling rate (%). C: Carbon content after annealing (ppm). P: Cleanliness after annealing (d 60X 400...%). J(: indicates the hardness after annealing (HR3oT), 100-0
．． 08x(C+1,000xP)-0,8xH>R>2
A method for producing a steel plate for easy-open cans having excellent can-opening properties, characterized in that the R is 0 and in the range of 45>R.