NL8501074A - METHOD OF MANUFACTURING A STEEL SHEET FOR AN EASY TO OPEN WITH A BETTER OPENING CAPACITY. - Google Patents

Description

• "β N.0.33.142 1

Method of manufacturing steel sheet for a can with easy-open end with better opening ability.

A method of manufacturing sheet metal tinplate 5 with an easy-to-open end with better openability includes an improvement in the conventional method, which includes the steps of hot rolling, a first cold rolling, annealing and a second cold rolling. The improvement lies in the implementation of the second cold roll reduction according to the formula: 100-0.08x (C + 1.000xP) -0.8xH> R> 20 and 10 45> R. This formula expresses the relationship between hardness, carbon content and purity after annealing, where R: the second cold reduction (%), C: the carbon content after annealing (ppm), P: the purity after annealing (d60x400 ....% ), and 15 H: the hardness after annealing (Hr 30T).

The present invention relates to a method of manufacturing steel sheet for cans with an easy-to-open end with improved opening ability.

20 In relation to hardness (Hr 30T), purity (d60x400% ...

according to JIS G055, the contents of which are incorporated herein by reference) and carbon content (ppm) after annealing, which follows the hot rolling and the first cold rolling, in the sheet metal fabrication process, the conditions for the second cold rolling Reduction after annealing to be determined in order to produce a steel sheet for cans with an easy-to-open end with better openability.

A number of different easy-open food cans have been used in recent years. In these cans, the can end plate has a suitable shape, is notched and a lip is attached to a notched end plate of the can such that the end of the can can be opened without using an opener by pulling on this lip . As the material for this type of easy-to-open can, aluminum sheet is generally used mainly due to good opening ability. Steel sheet (tinned sheet or tin-free steel) is used when the contents of the can are a matter for consideration. However, since aluminum is relatively expensive compared to steel, development of an inexpensive easy-open can of steel is urgently needed. To improve the ease of 40 can opening, namely better opening ability of 85SI 074 2 of the can, the following two main factors can be considered: one is thinning the remaining metal thickness after notching and the other is reducing the opening force without thinning the remaining metal thickness. For the first factor, a technique for thinning the remaining metal is a prerequisite that depends on considerations such as tearing at the notch, collision damage, when the can falls or other accidents, or pressing accuracy at the notching . These limiting considerations prevent the remaining metal thickness from being made sufficiently thinner.

Second, an improvement in the opening force without change of the residual metal thickness has in fact not been successfully accomplished to date, despite various limitations imposed on the material properties. Under the circumstances, the present invention has been developed as a result of extensive research to achieve a significant improvement in opening ability by simultaneously solving the foregoing two problems, that is, a method of manufacturing steel sheet for easily opening ends of cans, which not only provides good opening ability without changing the remaining metal thickness, but also thinning the remaining metal thickness.

The present invention includes that steel sheet for cans with an easy-to-open end can be manufactured by an improvement on the conventional method of manufacturing steel sheet for cans. This conventional method includes hot rolling, a first cold rolling, a tempering and a second cold rolling. By executing the second cold rolling mill according to the formulas 100-0.08x (C + l. OOOxP) -0.8xH> R 20 ... (1) 30 and 45> R ... (2), the desired results.

Formulas (1) and (2) are experiments obtained equations, in which R is the second cold-roll reduction (%), C is the carbon content (ppm), H is the hardness (Hr 30T) and P is the purity (d60x400 .. .%) to be. The hardness varies depending on the annealing method (annealing in the box, continuous annealing), annealing conditions (temperature, heating and cooling rates) and composition of the steel and generally ranges from 40 to 65 in Hr 30T.

8501074

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The carbon content can be controlled in the range below 1300 ppm (0.13%) in the case of sheet metal for cans, depending on the decarburizing state of the molten steel or presence or absence of decarburizing annealing in the intermediate process.

The purity, which depends on the deoxidation process of molten steel and the steel composition, generally ranges from 0.01 to 0.8.

In this regard, the basis upon which the reduction conditions of the second cold-rolling treatment are established, as stated above, comes from the result of in-depth investigations and observations, which relate to the relationship between properties and the ability to open up finishing materials, notching technique and strength, as will now be explained.

First, the relationship between sheet thickness of the final material, yield stress and opening ability will be discussed.

When considering the sheet thickness of the final material relative to its yield strength, which is determined by the square of the thickness of the end sheet times the yield stress of the final material (when the internal or external pressure applied exceeds this yield strength) plastically deformed), harder steels will be better thinned.

However, even if two steel grades have the same yield strength, the harder and thinner becomes more elastically deformed than the softer and thicker steel because elastic deformation in the third power is proportional to the steel thickness.

Furthermore, the force applied to the final material is greater at the heating temperatures intended for pasteurization.

Thus, the highest possible strength does not cause plastic deformation at such a time, ie, different combinations of steel thickness and yield stress can be discussed based on the yield strength of the final material, if no attention is paid to the action of elastic deformations .

The softer and thicker steel and the harder and thinner steel of equivalent strength are then machined to the same residual metal thickness after notching to compare openability.

The result shows that the harder and thinner steel plate has a poorer opening capacity than the softer and thicker steel 8501074 4 plate.

This result does not fit with most assessments that the thicker steel sheet would have higher stress concentration and thus be worse in opening ability if the two have the same Testes' running metal thickness after notching. It could be because the harder and thinner steel sheet can obtain the specific deformation, which is also required near the notched section, with less force in order to cause opening, i.e. fracture at the notched section. Therefore, when the residual metal thickness can be equalized, the harder and and thinner steel sheet, which is more disadvantageous with regard to the stress concentration at the notched section, is advantageous in opening ability.

Next, the limiting residual metal thickness (minimum residual metal thickness, which can be notched without causing any crack to the notched section) will be discussed.

The limiting residual metal thickness of the softer and thicker steel sheet, the thinner steel sheet cured by the second cold rolling and the thinner steel sheet cured by the heat treatment and steel composition controls were compared.

The results show that the limiting residual metal thickness of softening and thicker steel sheet and thinner steel sheet cured by the second cold rolling are approximately equivalent and relatively small, and also these steel sheets can be notched until they become relatively thin without any cracks while that of thinner steel sheet hardened by control of heat treatment and steel composition is relatively large.

It is believed that the reason for this is that the softer material is better notched with a greater notch reduction (plate thickness of the end minus the remaining metal thickness, divided by the plate thickness of the end) without the prevention of any cracks and the thinner plate thickness of the end will have a smaller notch reduction when the remaining metal thickness is equivalent.

Another reason is that the sheet cold cured by the second cold rolling will have a smaller limiting residual metal thickness, because the microstructure of this steel sheet develops elongated grains (roll texture) in the longitudinal direction relative to the sheet surface after the second cold rolling and this grain structure is suitable for reducing the limiting residual metal thickness.

The strength, which can withstand stress without any cracks in the notched section in the event of impact, for example, drops etc. (hereinafter referred to as "8501074" as "impact strength") will now be discussed.

In this regard, the smaller the remaining metal thickness, the smaller the impact strength, but when the remaining metal thickness is constant, the results show that the harder and thinner plate end has a greater impact strength than the softer and thicker plate end. It could be because the harder and thinner plate end leads to more elastic deformation than the softer and thicker plate and absorbs impact in the end as a whole, which reduces the stress concentration at the notched section.

Through various experiments involving the ability to open, limiting the remaining metal thickness or impact strength as necessary to produce an easy-to-open end, it has been found that when the fluidity of end material is the same , the thinner sheet, hardened by the second cold rolling, is better than a steel sheet for a can with an easy to open end. In this case, when a certain level of hardness is to be obtained by the second cold rolling, the lower the hardness of the sheet before the second cold rolling, the greater the rolling reduction of the sheet, while the greater the hardness for the second cold rolling, the smaller the roll reduction of the sheet.

When comparing two plates with the same hardness after the second cold rolling, the plate by means of the second cold rolling with a greater rolling reduction results in a smaller limiting residual metal thickness than the plate by means of the second cold rolling with a smaller rolling reduction. roller reduction.

This could be because the greater the roll reduction, the more the grain forms a microstructure elongated longitudinally relative to the sheet surface.

Also, the carbon content and the amount of non-metallic inclusions affect the limiting metal thickness remaining and as a result of testing this effect is represented by the formula: C + 1,000xP, where the carbon content in ppm is represented by C and the purity, which indicates the amount of non-metallic inclusions -35 (d 60x400 ...%) is proposed by P.

The greater than the value of C + 1,000xP, the greater the limiting metal thickness remaining.

However, it is recommended that this value of C + 1.0XxP should be determined with respect to hardness before the second cold rolling. For slabs that harden for the second cold rolling, 8501074 6 should necessarily have the value of C + 100xP, while for those softening a smaller value of C + 1,000xP will not be as necessary, because the limiting residual metal thickness must be improved due to a significant elongation of the grain by the second cold rolling.

In fact, an unnecessary drop in the value of C + 1,000xP for plates softening after annealing will unnecessarily increase material costs.

The relationship between the limiting residual metal thickness and hardness, carbon content and post-annealing purity, and second cold roll reduction is as noted above.

In any case, the upper limit of the second cold roll reduction should be determined based on consideration of openability, including the limiting metal thickness remaining.

As the roll reduction increases, the degree of material hardening is lowered, so even if the second cold roll reduction is made greater than that determined by formula (1), the limiting residual metal thickness will be adversely affected. In addition, the opening force will be increased with a more extremely developed brittleness of the material than would be obtained by reducing the final thickness due to material hardening or by improving the limiting residual metal thickness due to grain extension.

Also, when the second cold roll reduction is 45% or higher, an unfavorable effect on material embrittlement appears to be greater, and the limiting residual metal thickness will be increased and the opening force will also be increased.

Therefore, the decrease in the value of C + 1,000xP and the decrease in hardness to 45 or more in formula (1) will have almost no effect on the improvement of the opening force, but will only be unfavorable with respect to the cost. For such reasons, the upper limit of the second cold roll reduction is provided.

Also, there is the lower limit of 20% of the second cold roll reduction, because when the roll reduction is less than 20%, curing cannot be effected sufficiently and thus thinning of layer thickness 35 and extension of grain, which are suitable for the improvement of the limiting residual metal thickness cannot be obtained.

In this regard, the hardness after annealing is determined by the steel composition, the heat treatment conditions, etc., which factors are chosen with regard to cost, content corrosion resistance and other factors.

8301074 7

However, the second cold roll reduction after annealing should be selected depending on the type of end and type of notch.

Steel sheet to be manufactured in this manner is then subjected to a pretreatment, including degreasing and clean etching, and is subjected to the tin coating, electrochromic coating, phosphating and other conversion treatments to produce steel sheet for easy opening an end of a look.

The following describes the embodiments of the invention.

Fig. 1 shows the relationship between (carbon content + 1,000x brine) and second cold roll reduction and the ability to open the end plate with a hardness (Hr 30T) in the range of 48 to 53 after annealing.

Fig. 2 shows the relationship between (carbon content -f-100,000%) and second cold roll reduction and the ability to open the end plate with a hardness (Hr 30T) in the range 58 to 64 after annealing.

Table A

Chemical composition (weight Z)

Steel C Si Mn P Al Carbon content after decarburization_ A 0.010 0.01 0.33 0.018 0.081_ B 0.028 0.02 0.35 0.020 0.090_ C 0.052 0.02 0.33 0.022 0.073_ D 0.051 0.02 0.32 0.022 0.075 0.0019 _ (0.0022) _ E 0.051 0.02 0.32 0.022 0.070 0.016 _ (0.017) _

The steel grades presented in Table A were refined in the converter.

Steel A was decarburized and degassed until the molten steel had the chemical composition shown in Table A by degassing under reduced pressure and then transferred to the ingot fabrication, hot rolling and initial cold rolling by the conventional belting process and followed by either annealing in the box or glow continuously.

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Steel B was refined according to conventional refining, except for a lower carbon content, including the manufacture of ingot blocks, hot rolling and initial cold rolling and followed by either box annealing or continuous annealing.

Steel C was refined by ordinary refining to an average level of carbon content as a steel sheet for cans, including manufacture of ingot blocks, hot rolling and initial cold rolling and followed by either box annealing or continuous annealing.

Steel D was refined by the same ordinary refining as steel C until hot rolling. In the case where continuous annealing is used after the first cold rolling, it is decarburized before the first cold rolling, and in the case that continuous annealing is not used, it is annealed in the decarbonizing box after the first cold rolling without decarburization for the first cold rolling.

Steel E was prepared according to the same preparation process as steel D, except that decarburization was intentionally stopped earlier to control the carbon content.

The carbon content of the steels D and E after decarburization, shown in Table A without brackets, are values after decarburization after the first cold rolling and those shown in brackets are values after decarburization before the first cold rolling.

In case the hardness after the first cold rolling is 40 to 55 in Hr 30T, annealing in the crate or decarburizing annealing in the crate 25 was used and in case the hardness is 55 to 65 in Hr 30T, continuous annealing was used .

These steels with predetermined thickness and hardness so that their yield strength can be equalized (square of thickness times yield stress of material can be constant) were then subjected to a second cold rolling treatment.

After the second cold rolling, the steels were purified and tin-coated in a ferrous bath followed by machining.

The end had a notch with a diameter of 58 mm for the fully open end. Riveting was replaced by brazing to affix a tin plate tab at the end in the same specific location as the production end, since it has not been practical to produce a metal mold suitable for a number of thicknesses available.

40 The acceptance of opening ability was based on the 8501074 * - ▼ 9 maximum tearing force following the initial opening force at the remaining metal thickness, that is, the limiting remaining metal thickness of each material plus 10 µm and the rating was performed based on a glow of 2.5 (Hr 30T 52 to 58) and a sheet thickness of 0.23 mm, which are used as acceptance criteria of the fully open end of the moment. The results are presented in Fig. 1 and in Fig. 2. Fig. 1 gives the results relating to a hardness of 48 to 53 in Hr 30T for the second cold rolling of plates annealed by annealing in the box or decarburizing annealing in the box and FIG. 2 shows the relationship between ( C + 1,000xP) and the second cold roll reduction to openability with a hardness of 58 to 64 in Hr 30T for the second cold rolling of the sheet annealed by the continuous method. The values marked with a triangle in the figures show those values where an improvement is found which is less than 7.5%, values marked with a single circle are those where an improvement is found from 7.5 to 15% and values with double circles mean an improvement of more than 15% with regard to the acceptance level (opening force with a temper of 2.5 and a thickness of 0.23 mm).

Those values enclosed by a dashed line in the figures are within the scope of the invention and show that the harder and thinner steel sheet manufactured according to formulas (1) and (2) (provided the yield strength is constant) finds an improvement at more than 7.5% in opening ability and better than an easily opening end material. The preferred embodiments herein relate to tin-plated plates, but other embodiments with a surface treatment of not only tin-plated plate, but tin-free steel and other tin-plated plates for conversion treatments will also find a satisfactory improvement.

Also, the attachment of the lip is not limited to soldering, the one mentioned herein for convenience of the test only and bonding adhesion applications as reported in JPI Journal 1984, Vol. 22, No. 4 are also suitable.

15 012).

Claims (3)

A method of manufacturing sheet metal for cans with easy-to-open ends, with better openability, comprising the steps of hot rolling, a first cold rolling, annealing and a second cold rolling, characterized in that the performs second cold rolling according to the formulas 100-0.08x (C + 1.000xP) -0.8xH> R> 20 ... (1) and 45> R ... (2), where R: the second cold reduction (%), C: the carbon content after annealing (ppm), 10 P: the purity after annealing (d60x400 ....%), and H: the hardness after annealing (Hr 30T). 2. Method according to claim 1, characterized in that the hardness after the first cold rolling is from 40 to 55 in Hr 30T and annealing in the box or decarburizing annealing in the box is used. Method according to claim 1, characterized in that the hardness after the first cold rolling is from 50 to 65 Hr 30T and continuous annealing is used. *********** 8501074