JPH0641681A - Steel sheet for dwi can excellent in flange workability - Google Patents

Abstract

PURPOSE:To provide a steel sheet for DWI can capable of meeting the recent demand for reducing thickness by providing superior flange workability, DWI workability equal to or higher than that of the conventional batch annealed steel sheet, and high pressure-resisting strength. CONSTITUTION:This steel sheet has a composition which contains 0.010-0.060% C, 0.05-0.50% Mn, 0.015% or less P, 0.015% or less S, 0.020-0.100% acid soluble Al, and 0.0003-0.0070% N and where the content of solid solution C and the content of (solid solution C and solid solution N) are regulated to 0.0005% or higher and 0.0010-0.0020%, respectively. Further, this steel sheet has 46-60 hardness, (20 to 42)kgf/mm<2> yield strength, 9.0-11.5 crystalline grain No., and 1.8 or lower degree of elongation. This steel sheet is soft and easily worked at the time of DWI working and is age-hardened at the time of drying and increased in pressure-resisting strength, thereby, workability can be combined with pressure-resisting strength and this steel sheet can meet with the recent demand for reducing thickness.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a DWI can (Drawn).
steel sheet for and wall ironed can), which has excellent flange formability after DWI processing, is easy to perform DWI processing and neck processing, and has the property of being hardened when coating is dried after DWI processing and improving the can body pressure strength. It relates to a steel plate for use.

[0002]

2. Description of the Related Art Can steel plates such as tin plates plated with tin or tin-free steel plates with chromic acid are widely used for food cans, aerosol cans and easy open cans.

Conventionally, many cans made of these steel plates are three-piece cans consisting of a lid, a body, and a bottom.
In recent years, a technique has been developed in which a body and a bottom are integrated and a two-piece can including two parts is made from a steel plate together with a lid. Two
Since the piece can has the advantage of low can manufacturing cost, the two-piece can tends to grow in place of the three-piece can. Two-piece cans are subjected to severe processing such as multi-step drawing or DWI processing (that is, ironing is performed after deep drawing), and not only corrosion resistance but also excellent workability is required.

DWI cans are generally manufactured through the following can manufacturing process. First, a cup-shaped press machine is used to punch a disk-shaped blank plate from a steel strip, and the blank plate is shallow-drawn using a punch and a die to form a cup. Next, a punch and a die having a clearance smaller than the thickness of the side wall of the cup are used to draw the side wall while squeezing it to reduce the thickness of the side wall, thereby forming a cup-shaped can body having a predetermined depth ( This molding is referred to as DWI processing), and the bottom of the can body is made to collide with a bottom former to form the can bottom into a convex dome shape. DW
During the I processing, due to the anisotropy of the workability of the material, a so-called earring phenomenon occurs in which the height of the cylinder after processing corrugates along the circumferential direction. The top convex portion of the body of the earring phenomenon is called an ear or an ear. On the next trimmer machine, the ears are trimmed to even the top of the torso.

Further, the can body is washed and dried by a washer machine. Then, using a printer, the outer surface of the can is printed and painted, and the bottom of the can is painted. The coating is then dried in a pin oven. Then, the inner surface is painted and dried in a belt oven. Then, with a necker / flanger machine, multi-stage necking processing is performed to reduce the opening diameter of the can body, and in order to attach a lid to the opening end of the can body, flange processing is performed at the opening end portion so as to extend outward in the diametrical direction. In this state, the can body is shipped from the can manufacturing company to the contents filling company, and after filling the contents, the lid is wound and tightened to become a canned product.

[0006] Important properties required of the steel sheet for DWI cans are DWI workability, neck workability, flange workability, and pressure resistance and paneling strength after forming a can body. The DWI processability refers to a performance in which the die wear is small, the die galling is small, and the processing energy is small in the DWI process. Neck processability refers to the performance in which wrinkles do not occur in multi-step necking. The flanging property refers to the ability to hardly cause cracks that cause leakage of the contents of the can to the flange portion during flanging, that is, defects called flange cracks. The compressive strength means a critical internal pressure of a can that causes a buckling phenomenon in which a weak portion of the can body protrudes to the outside due to the internal pressure after the lid is wound. It is the can bottom and the lid that are weak against the internal pressure of the can, and the pressure resistance strength is often controlled by the mechanical strength of the can bottom and the lid. The paneling strength refers to a critical external pressure at which the body of the can is dented inward by external pressure after the lid is wound and tightened. The strength against external force during handling such as packing of canned goods, transportation, unpacking, and dropping in a vending machine is often represented by this paneling strength.

Conventionally, as such a steel plate for a DWI can,
For example, batch-annealed materials such as those obtained by batch-annealing B-added Al-killed steel (JP-A-53-48913) and batch-annealed Cu-added low-carbon steel (JP-B-52-16965) are used. It had been. This is because the batch annealed material is more stretched and more excellent in deep drawability, and is generally considered to be suitable for DWI processing applications. Especially, in forming a DWI can, it is very important to have good flange formability, and the defect rate is several tens of pp.
Must be kept below m. For that reason, a batch annealed material that has been elongated as a steel sheet and has an excellent r value has been conventionally applied.

[0008]

On the other hand, the DWI has been conventionally used.
The plate thickness of the steel plate for cans was generally 0.30 to 0.35 mm, but in recent years, from the viewpoint of resource saving, the plate thickness has become thinner. However, the conventional batch-annealed steel sheet for DWI cans has a problem that the pressure resistance and the paneling strength are reduced as the thickness is reduced. The pressure resistance of the can is (plate thickness) ²
Since it is determined by x (yield strength), thinning causes a decrease in pressure resistance. Therefore, it is necessary to increase the yield strength of the material in order to reduce the thickness while ensuring a predetermined compressive strength.

However, since batch annealed steel sheets are generally soft, in order to increase the yield strength, it is necessary to add a strengthening element to make them a relatively high alloy component, and vice versa.
There is a problem that WI processability is deteriorated. That is, when the strength of the batch annealed steel sheet is increased, galling is likely to occur during DWI processing, wear of the die is large, and processing energy is increased. Further, when the strengthening element is a solid solution strengthening element, there is a problem that the flange formability is deteriorated.

The paneling strength has the same problem. Further, the batch annealed steel sheet strengthened by adding a strengthening element has a large deformation resistance after DWI processing, and thus has a drawback that wrinkles are likely to occur in multi-step necking processing.

The continuous annealing method is an annealing method suitable for producing a steel plate for a hard can. Therefore, it is easier to increase the yield strength and the compressive strength of the continuous annealed steel sheet without adding a strengthening element as compared with the batch annealed steel sheet. However, since a continuous annealed steel sheet having a high yield strength has a large deformation resistance during and after DWI processing, it has the same DWI workability and neck workability as the batch annealed steel sheet strengthened by adding a strengthening element. There was an inferior problem. Further, since the continuously annealed steel sheet contains a large amount of solid solution C, there is a problem that the flange formability is extremely poor.

As described above, the conventional steel sheet for cans for DWI should have both workability such as DWI workability and neck workability and can body strength such as pressure resistance and paneling strength when thinned. There was a problem that I could not. Further, the conventional steel sheet for cans for DWI has a fundamental defect that the flange formability is inevitably deteriorated when attempting to cope with thinning.

The present invention solves such a problem and has excellent flange formability, DWI formability and neck formability equal to or higher than those of conventional batch annealed steel sheets for DWI, and after DWI processability. DWI that can be made thinner due to its high pressure resistance and paneling strength
The purpose is to provide a steel sheet for cans.

[0014]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted various studies on various properties required for a steel sheet for a DWI can, and as a result, have comprehensively analyzed the above various properties and their controlling factors. Then, it has been found that a steel sheet for a can in which the components of the steel sheet, in particular, the contents of solid solution C and solid solution N, and the yield strength, hardness, and microstructure are controlled can industrially be made thinner.

The present invention is constructed on the basis of this finding, and the gist thereof is C: 0.010-0.
060%, Mn: 0.05 to 0.50%, P: 0.01
5% or less, S: 0.015% or less, acid-soluble Al: 0.0
20-0.100%, N: 0.0003-0.0070
%, With the balance being iron and inevitable impurities, the amount of solid solution C being 0.0005% or more, and the total amount of solid solution C and solid solution N being 0.0010% to 0.0020%. HR30 of 46 to 60 containing solid solution C and solid solution N
It has a T hardness and a yield strength of 20 to 42 kgf / mm ² ,
It is a steel plate for a DWI can having a JIS grain size number of 9.0 to 11.5 and a crystal grain structure having an elongation of 1.8 or less and excellent flange formability.

The present invention will be described in detail below. The contents of solute C and solute N are the most important constituent features of the present invention. From a metallurgical point of view, the DWI can has a characteristic different from other types of cans in that it is subjected to high temperature aging of about 200 ° C. in the coating drying process after DWI processing. Therefore, the present inventors have paid attention to this point, and by adding an appropriate amount of solute C and solute N to the steel sheet, it has a softness equal to or higher than that of the batch annealed steel sheet for DWI during DWI processing. Easy to do,
In the coating drying step after DWI processing, it was examined in detail whether the yield strength could be increased by the age hardening effect of solid solution C and solid solution N. As a result, by controlling the amounts of solute C and solute N within the range of the steel of the present invention,
I have found that I can achieve this goal.

The age hardening action of steel increases the yield strength, which governs the compressive strength and paneling strength, but does not increase the tensile strength, which is the deformation resistance during neck processing. The tensile strength of the portion to be necked causes recovery softening rather than the coating drying step, and the neckability is excellent. From such a viewpoint, the steel of the present invention has a DW at the time of thinning, which has been impossible in the past.
For the first time, it is possible to achieve both workability such as I workability and neck workability, and pressure resistance strength and paneling strength, which are strengths of the can body after it has been formed.

Solid solution C and solid solution N are conventionally considered to be harmful to the flange formability. However, as a result of detailed investigation of the effects of the solid solution C and solid solution N amounts and the flanging speed on the flanging processability, the inventors of the present invention certainly confirmed that when the flanging rate was low, the aluminum killed as was conventionally considered. It is essential to have an extremely low amount of solute C and solute N, which is equivalent to that of batch annealed steel sheets, but the flanging speed is today's D.
It has been found that when the total amount of the solid solution C and the solid solution N is 0.0020% or less, the flange formability is practically sufficient at the high speed equivalent to that of the WI can manufacturing line.

From the above process, the amounts of solid solution C and solid solution N were limited as follows. That is, first, if the amount of solute C is less than 0.0005%, a sufficient age hardening effect cannot be obtained and the pressure resistance at the time of thinning becomes insufficient.
It is necessary to contain 0.0005% or more. Also, solid solution C
When the total amount of the solute N is less than 0.0010%, a sufficient age hardening effect cannot be obtained, and the pressure resistance at the time of thinning becomes insufficient. Therefore, the lower limit is limited to 0.0010%. Further, if it exceeds 0.0020%, not only the flange workability and neck workability are deteriorated as described above, but also the DWI workability is deteriorated due to progress of solid solution hardening before coating drying. Therefore, the upper limit is set to 0. It was limited to .0020%.

The steel sheet containing solid solution C and solid solution N as described above achieves the object of the present invention in combination with the components described below. When the C content is less than 0.010%, the softening proceeds excessively, and the HR30T hardness is 46 or more and 20 kg.
Since the yield strength of f / mm ² or more cannot be secured, and the pressure resistance and the paneling strength when thinned are insufficient.
It is necessary to add 010% or more. On the other hand, this amount is 0.0
If it exceeds 60%, it will be hardened and the HR30T hardness of 60 or less and the yield strength of 42 kgf / mm ² or less cannot be secured, and the DWI workability and neck workability will deteriorate, so the upper limit is limited to 0.060%. There is a need to.

If Mn is less than 0.05%, hot brittleness occurs and a steel sheet for DWI can cannot be manufactured.
It is necessary to add 0.05% or more. On the other hand, this amount is 0.
If it exceeds 50%, the steel sheet is excessively hardened to deteriorate the DWI workability and the neck workability, so the upper limit is 0.50.
Must be limited to%.

Although it is not necessary to add P intentionally, it is an unavoidable impurity element that significantly hardens the steel sheet, and if its amount exceeds 0.015%, the steel sheet excessively hardens and the DW
Since the I workability and neck workability deteriorate, it is necessary to limit the upper limit to 0.015%.

Although it is not necessary to intentionally add S, 0.015 is an unavoidable impurity element that promotes hot brittleness.
%, The DWI can steel sheet cannot be produced due to hot brittleness, so the upper limit must be limited to 0.015%.

The acid-soluble Al is 0.020% in order to fix a part of N contained in the steel sheet as aluminum nitride and to control the total amount of solid solution C and solid solution N to be not more than the upper limit of the above range.
It is necessary to add above. On the other hand, if this amount exceeds 0.100%, the amount of N fixed as aluminum nitride becomes excessive, the amount of solid solution N becomes insufficient, the age hardening action decreases, and the pressure strength becomes insufficient. It is necessary to limit it to% or less.

N is required to be added in an amount of 0.0003% or more in order to control the total amount of solid solution C and solid solution N to be not less than the lower limit of the above range. On the other hand, if this amount exceeds 0.0070%, the steel sheet is excessively hardened and the DWI workability and neck workability are deteriorated. Therefore, it is necessary to limit the upper limit to 0.0070%.

The steel sheet for a DWI can having the above components can achieve the object of the present invention in combination with the mechanical properties and crystal grain structure described below. HR30T of steel plate
The hardness should have a value of 46 or more at the time when the steel plate manufacturer ships the steel plate to the can manufacturing company.
If it is less than 46, the pressure resistance and the paneling strength of the DWI can at the time of thinning become insufficient. On the other hand, when the hardness exceeds 60, the steel plate is excessively hardened and the DWI workability and the neck workability are deteriorated. Therefore, it is necessary to limit the upper limit to 60.

The yield strength of the steel plate must be 20 kgf / mm ² or more at the time when the steel plate manufacturer ships the steel plate to the can manufacturing company. This is because this yield strength is 20kgf / mm
^When it is less than ² , the pressure-resistant strength and paneling strength of the DWI can when thinned are insufficient. On the other hand, this yield strength is 42 kg
If it exceeds f / mm ² , the steel plate becomes excessively hard and the DWI workability and neck workability deteriorate, so the upper limit is 42 kgf /
Must be limited to mm ² . If the steel sheet manufacturer does not show a yield point at the time of shipping the steel sheet to the can manufacturing company, 0.2% proof stress must be within the limited range of the yield strength. The reason is based on the reason for limiting the yield strength.

The JIS grain size number of the steel sheet is 9.
If it is less than 0, the flange formability deteriorates, so the lower limit was set to 9.0. Further, if it exceeds 11.5, the steel sheet is excessively hardened and the DWI workability and the neck workability are deteriorated, so the upper limit was limited to 11.5. Steel plate J
If the IS crystal grain elongation is higher than 1.8, the flange formability also deteriorates, so the upper limit must be limited to 1.8.

Further, a method for producing the steel of the present invention will be described.

The molten steel having the above-mentioned specific components is melted by a usual method, and is made into hot steel pieces by the continuous casting method or the ingot-making and slab-rolling method, and is subjected to hot rolling. The heat treatment conditions for the billet prior to hot rolling may be any of the commonly used methods. That is, the hot steel slab may be directly sent and rolled, or reheated in a heating furnace. In particular, in order to manufacture a steel sheet for a DWI can having excellent flange formability, a steel piece is formed by a continuous casting method, cooled to below the Ar ₃ transformation point, and then T * = 6875 / (3.865-log [Al% + 0. 01
5]) It is preferable to reheat to a temperature range of T * ° C. or less satisfying −250 and to subject it to hot rolling. Although the hot rolling may be performed by any method that is usually performed, it is preferably wound at a temperature of 600 to 710 ° C.

Then, after pickling by a usual method, it is cold-rolled and subjected to continuous annealing. The continuous annealing can be performed by any method as long as the total amount of solid solution C and solid solution N, hardness, yield strength, grain size number and crystal grain elongation of the product steel sheet satisfy the above-mentioned claims, but the recrystallization temperature or higher. After performing recrystallization annealing at a temperature of 850 ° C. or lower for 5 seconds to 180 seconds, 5 to 250 ° C.
/ S cooling rate, integrand function exp [-1010
0 / T] (where T is the overaging treatment temperature at time t in Kelvin units) from time t = 0 (when the overaging treatment start time is t = 0) to t = t ₁ (t ₁ is It is preferable to perform the overaging treatment such that the heat activation stroke index defined by the value integrated to (the end time of the overaging treatment expressed in seconds) is 5.1 × 10 ⁻⁶ or more. The annealing conditions may be determined so as to satisfy the characteristics of the product steel sheet within the range.

Then, temper rolling is carried out by a usual method, and surface treatment which is usually carried out is applied. The type of coating applied to the surface of the steel of the present invention does not matter. That is, the effect of the present invention can be exerted by any coating that can be used for the steel sheet for a DWI can, such as tin plating, aluminum plating, or a polymer organic film attached.

[0033]

EXAMPLE Steels having the components shown in Table 1 were melted in a converter,
After continuous casting into hot steel billet, cool it to room temperature,
Reheat to 150 ℃ and hot roll to a thickness of 3.0mm.
The hot-rolled steel strip was wound at 60 ° C., pickled, cold-rolled, and the cold-rolled steel strip was annealed in a continuous annealing furnace or a batch annealing furnace. In the case of continuous annealing, cold rolled steel strip is 690
After recrystallization annealing at 0 ° C., primary cooling was performed at a cooling rate of 150 ° C./s to the overaging treatment temperature, and overaging treatment was performed at a temperature of 300 ° C. for 300 seconds. In the case of batch annealing of a comparative machine (outside the present invention), cold rolling steel strip was held at 680 ° C. for 15 hours to perform batch annealing. The annealed steel strip thus obtained is temper-rolled at a rolling reduction of 10.0% to obtain a sheet thickness of 0.24 mm.
Of the above, and tin-plated to obtain a steel plate for a DWI can.

Solid solution C of the steel sheet for DWI can thus obtained
Amount, total amount of solid solution C and solid solution N, hardness, yield strength (0.
(Including 2% proof stress), grain size number and grain elongation
Shown in. Here, the amount of solute C and the amount of solute N were measured by an internal friction method by taking a sample from the annealed steel strip before temper rolling. The hardness was measured according to JIS Z2245 by taking a sample from the tin-plated steel sheet for a DWI can. The yield strength was measured according to JIS Z2241 by taking a sample from the tin-plated steel sheet for a DWI can. The grain size number and the elongation were measured in accordance with JIS G0552 by taking a sample from the tin-plated steel sheet for a DWI can.

The DWI of the steel sheet for a DWI can thus obtained
Table 3 shows the workability, neck workability, flange workability, and pressure resistance. Here, the evaluation of the DWI processability is performed by actually performing DWI processing of these steel sheets for DWI cans using a DWI processing tester in the laboratory of the present inventors and measuring the third-stage ironing forming force. I did it in. The ironing forming force of a conventional steel sheet (batch annealed steel sheet) having the same plate thickness as the comparative steel was also measured at the same time, and the average value of the ironing forming force of the steel sheet of the example was
Those of the conventional steel sheet and below were evaluated as "pass", and those of the conventional steel sheet exceeding that were evaluated as "fail".

The neck workability was evaluated by actually making a can of these steel sheets for DWI cans using a DWI working tester in the laboratory of the present inventors and performing heat treatment equivalent to the coating and drying step in an atmosphere drying furnace. After the application, a necking tester in the same laboratory was used to actually perform 3-step necking and observe the occurrence of wrinkles. Then, those in which no wrinkles were observed at all in all the tested can bodies were evaluated as “pass”, and those in which one wrinkle occurred were evaluated as “fail”.

The flange workability was evaluated by actually flanging the same three-stage neck processed can body used in the neck workability evaluation with a laboratory high-speed flanging tester to generate flange cracks. The rate (the ratio of the number of canned flanges to the total number of cans tested) was determined. A flange crack occurrence rate of a conventional steel sheet (batch annealed steel sheet) having the same plate thickness as the comparative steel was also measured at the same time, and a flange crack occurrence rate of the steel sheet of the example was “passed” if it was less than that of the conventional steel sheet.
It was evaluated as “Failure” when the conventional steel plate exceeded that.

The pressure resistance was evaluated by using a laboratory DWI processing tester to actually make cans of these steel sheets for DWI cans, and after applying a heat treatment equivalent to the coating and drying process in an atmosphere drying furnace, The opening was sealed with a rubber liner, compressed air was gradually introduced into the can body, and the critical pressure at which the can bottom caused buckling was determined. In the case of such a measuring method in the laboratory of the present inventors, it is known that if the critical pressure is 7.5 kgf / cm ² or more, it can be practically used even by the customer, so that the result of the critical pressure is 7 .5
Those with kgf / cm ² or more were evaluated as “pass”, and those with less than that were evaluated as “fail”.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

In Tables 1 and 2, numerical values outside the scope of the present invention are underlined. As can be seen from Tables 1 to 3, product numbers 1 to 8 within the scope of the present invention
Has excellent DWI workability, neck workability, and flange workability as well as sufficient pressure resistance, and has succeeded in reducing the thickness to 0.24 mm. On the other hand, the product numbers 9 to 12, which are outside the scope of the present invention, cannot achieve both workability and pressure resistance, and cannot be made thinner.

[0043]

INDUSTRIAL APPLICABILITY The present invention succeeds in achieving both can strength, flange formability, neck formability, and DWI formability, which cannot be achieved by the conventional techniques, in thinning the steel sheet for DWI can. DWI with excellent workability
It provides steel sheets for cans, and its industrial value is extremely high.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Kono 1-1, Toibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Yawata Works

Claims (1)

[Claims] 1. C: 0.010 to 0.060% by weight%, Mn: 0.05 to 0.50%, P: 0.015% or less, S: 0.015% or less, acid-soluble Al : 0.020 to 0.100%, N: 0.0003 to 0.0070%, the balance being a component consisting of iron and unavoidable impurities, and the amount of solid solution C being 0.0005% or more, solid solution C And a solid solution C and a solid solution N such that the total amount of the solid solution N is 0.0010% to 0.0020%, and an HR30T of 46 to 60.
Hardness, yield strength of 20-42 kgf / mm ² ,
The IS grain size number is 9.0 to 11.5 and the elongation is 1.
A steel sheet for a DWI can having excellent flange formability, which has a crystal grain structure of 8 or less.