JPS63134645A - Steel sheet for di can excellent in stretch-flange formability - Google Patents

Abstract

PURPOSE:To improve stretch-flange formability after DI working and also to uniformize material quality, by specifying respective quantities of C, Mn, P, Al, N, and Fe and also by carrying out continuous annealing under the prescribed conditions. CONSTITUTION:This steel sheet for DI cans has a composition consisting of, by weight, 0.004-0.06% C, 0.05-0.5% Mn, <=0.02% P, 0.02-0.1% acid-soluble Al, <=0.007% N, and the balance Fe. Subsequently, recrystallization annealing is applied, e.g., at a temp. between the recrystallization temp. and 850 deg.C for 5-180sec, followed by cooling at 5-250 deg.C/sec cooling rate and overaging treatment at 250-500 deg.C. In this way, the steel sheet for DI cans having a tensile strength of <=42kgf/mm<2> and a grain structure of JIS grain size number 8.5-11.5 can be obtained.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is applied to DI cans (Draw & Ironed Cans).
) This relates to a steel plate for DI cans that has excellent stretch flange formability after DI processing, is easy to perform DI processing, and has improved pressure resistance by hardening during paint baking after DI processing.

(Conventional technology) Tin-plated steel sheets are tin-plated steel sheets, or tin-free steel sheets are treated with chromic acid (hereinafter referred to as T and F).
Surface-treated steel sheets such as steel sheets (referred to as "S") are used in food cans, aerosol cans, and easy-open cans (two-line cans).

In recent years, these surface-treated steel sheets have been subjected to severe processing such as multi-stage drawing processing or DI processing (Draw and Ironing processing, i.e., ironing processing is performed after deep drawing processing)9. It is also necessary to possess gender.

The manufacturing process for DI cans involves shallow drawing a steel plate using a punch and die to form a cup, and then using a punch and die with a clearance smaller than the thickness of the side wall of the cup to draw and stretch the side wall. (2) A container (cup) with a predetermined depth is formed, and the end of the cup is flanged for winding a lid.

The characteristics required for steel sheets for DI cans include good workability during DI processing, no galling and low processing energy, excellent stretch flange formability after DI processing, and can body As such, high pressure resistance is required.

Conventionally, materials for such DI cans include, for example, B-added At.
Killed steel box annealed (Japanese Patent Application Laid-open No. 53-48913)
, box annealed Cu-added low carbon steel (Special Publication No. 1972-
16965), box-annealed materials were mostly used. Box-annealed materials elongate better and have better deep drawability.
This is because it was thought to be suitable for general (2DI) processing applications.

In particular, good stretch flange formability is extremely important in the molding process of 01 cans, and the defect rate is several tens of pp.
It is necessary to keep it below m. Therefore, it stretches as a steel plate,
Box-annealed materials with excellent r-values and low solid solution C in steel have been used in the past.

(Problems to be solved by the invention) On the other hand, in recent years, the thickness of DI cans has become thinner and thinner.
The demand for increasing pressure resistance is also becoming increasingly strong.

The compressive strength of the can body is determined by (plate thickness) x (strength), and to make it thinner, it is necessary to increase the strength of the material, but box annealed materials are generally soft and it is difficult to make them thinner. In order to improve the strength, it is necessary to add a strengthening element to make the alloy a relatively high alloy component, and in this case, there is a problem that DI workability deteriorates.

Furthermore, if the strength of the steel plate is increased, it becomes more likely to cause scuffing during DI processing, and the processing energy also increases.

Recently, manufacturing steel sheets for DI cans by continuous annealing has been considered, but it has not yet been achieved to prevent small cracks from forming during flange forming during DI can processing.
In addition, galling is also observed here and there.

An object of the present invention is to provide a container material for DI cans, which has excellent elongation 7 lunge formability, does not cause galling, is easy to perform DI processing, and has high pressure resistance after DI processing.

(Means for Solving the Problems) The present inventors have determined that, as a result of various studies, we have determined that the steel sheet for DI cans has the following properties: As a result, they newly discovered that a continuously annealed steel sheet with specific strength and grain size is superior, and the present invention was completed based on this new finding.

The present inventors first deeply studied the stretch flange formability after DI processing, and found that the stretch flange formability after DI processing, that is, after significant processing, is different from the stretch flange formability of the steel sheet itself, and is rather different from conventional knowledge. On the other hand, if the tensile strength of the steel plate is 42Klif/- or less and the grain size number is 8.5 to 1
1.5, C: 0.0040-0.0600%, Mn
: 0.05~0.50%, 7V, 20.020~0
．． 100%, P: 0.020' or less, N: 0.007
It has been newly discovered that a continuously annealed material with a steel composition of 0% or less has better stretch flangeability after DI processing despite having solid solution C.

The present inventors discovered that in the continuously annealed material, the strength of the can body is significantly increased by the paint baking applied after DI processing, and as a result, the pressure resistance strength is also increased (hereinafter this property is referred to as BH property). Ta. In other words, by using the continuous annealing material which is softer than the box annealing material: it is softer during DI processing, and therefore has excellent DI workability, and after painting baking, it has the excellent characteristics of having a post-compressive strength higher than that of box annealing. It has been found. This means that if the strength of the material is the same, the pressure resistance of the can body can be higher with the continuously annealed material, so this has great industrial value.

The present invention will be explained in detail below.

First, the tensile strength of the product plate (steel plate) will be explained with reference to FIG. If the tensile strength is large, the forming load and forming energy during DI processing will become large, making processing difficult and galling more likely to occur, so the upper limit is set at 42Kqf/-
shall be. A preferred range is a tensile strength of 40 Kyf/- or less.

Figure 1 shows c: 0.0040~o, oso%, M
n: O, 15-0.60%, P: 0.006-0.
030%, At: 0.005-0.070%, N: 0
．． 0.0070% or less steel is melted in a vacuum melting furnace, and the steel plate for DI processing manufactured on the laboratory pilot line (2) is measured by the tensile strength of the fission plate and the total forming energy in the DI test forming machine (= total forming energy in the post-forming paint baking treatment). The relationship between the compressive strength and the annealing method of the DI cans is shown below.

As can be seen from Figure 1, the tensile strength is 42 f/Iul.
If the value exceeds 1, the total molding energy increases significantly and galling occurs frequently, making DI molding difficult. In order to keep the total forming energy stably low (= tensile strength is 40 to 9f)
/- or less, the yield point is 36 h f /mj or less, more preferably the tensile strength is 37 Kgf/- or less, the yield point is 30 Kqf
/- or less (preferably two).

Still, the compressive strength increases as the tensile strength increases, but the compressive strength of the continuously annealed material is about 1 to 2 K9flcrl higher than that of the box annealed material even if the tensile strength is the same. In order to ensure H properties as described above, it is preferable that the amount of solid solute C in the Nisei relief plate is 5.0 ppm or more.

Next, crystal grain size will be explained.

Figure 2 shows C: 0.0044-0.080%, Mn: 0
．． 16-0.57%, p: o, o o s ~0.
030%, Aε: 0.007~o, oeo%, N: 0.
0020~0.0070% steel is melted in a vacuum melting furnace,
Surface-treated steel sheets for DI machining manufactured on a laboratory pilot line (two of them) show the relationship between the JIS grain size number, the processing rate until breakage occurs in stretch flange forming after DI machining, and the pressure resistance strength in relation to the annealing method. .

It has been found that a stretch flange processing rate of 9.0 or more is evaluated as acceptable even by consumers in the laboratory measurement method of the present inventors.

As can be seen from Fig. 2, the stretch flanging rate improves as the grain becomes finer (the larger the grain size number), and in order to secure a stretch flanging rate of 9.0% or more, in the case of continuously annealed material, A grain size number of 8.5 or more is required. Also, contrary to expectations, the stretch-flange formability of the continuously annealed material is better than that of the box-annealed material. On the other hand, the finer the grain, the better the stretch flange formability and pressure resistance, but the harder the steel becomes.
If the grain size number exceeds 11.5, the total forming energy during DI forming will increase significantly and galling will occur.
I processing becomes difficult. Therefore, the grain size number is 8.5
~11.51-Specify. The preferred range is 9.0-11
．． It is number 0.

Next, the steel components will be explained.

Since C hardens steel, its upper limit is set to o, o6oo%. Reducing the amount of C is effective for softening, but
If C is reduced to less than 0.0040%, solid solution C will decrease significantly and BH properties cannot be obtained, so the lower limit is set to 0.0040%. The preferred range is 0.0040-0.0400%. Mn needs to be contained in an amount of 0.05% or more to prevent hot embrittlement caused by S, but if it exceeds 0.50%, it will harden the steel like C and lose the characteristics of the present invention. The preferred range is 0.10 to 0.30 inches. Al! is used as a deoxidizing agent to reduce oxide inclusions that are harmful to workability, and at least as an acid-soluble M to suppress hardening due to strain aging during surface treatment by fixing N in steel. 0
．． It is necessary to contain 0.020%. But 0.100%
Exceeding this will harden the steel and increase surface flaws.

The preferred range is 0.030 to o.o.so%. P and N are elements that significantly harden steel, and by lowering both P and N, a more remarkable softening effect than previously thought can be obtained. In order to obtain a steel plate for DI processing specific to the present invention, the upper limit of P is 0.020% and the upper limit of N is 0.02%.
．． 0070%. The preferred range of N is 0.003
It is 0% or less.

Especially tensile strength 37Kgf/aj or less, yield point 30K9
When manufacturing a steel plate that is softer than f/-i and has excellent DI workability, c: 0.0040 to 0.0800%.
, Mn: 0.10-0.25%, acid soluble A! :
Preferably, the content is 0.030 to 0.080%, P:O, 015% or less, and N: 0.0025% or less.

The steel components in the present invention are as described above, but since S becomes inclusions in the steel and causes surface defects of the steel plate and cracking during processing, it is preferable that the content is 0.015% or less. Still necessary (from the second point, the steel components of the present invention further contain not more than 0.050% of B, which is a carbonitride-forming element, and 0.10%).
% or less of Cr. By adding these elements, a steel plate with excellent DI workability can be stably manufactured.

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

The steel having the above-mentioned specific components is bath-produced by a conventional method, and is made into a steel billet by a continuous casting method or an ingot-forming and blooming rolling method, and is subjected to hot rolling. The heat treatment conditions for the steel billet prior to hot rolling may be any conventional method.

That is, the hot piece may be directly sent and rolled, or may be reheated in a heating furnace. In order to produce a steel plate for DI processing that is particularly soft and has excellent DI workability and elongation 7 lunge formability, it is necessary to produce a steel plate using a continuous casting method, cool it to below the Ar transformation point, and then heat it in a temperature range of 1150°C or less. It is preferable to reheat and subject to hot rolling.

Hot rolling can be done by any conventional method, but 6
It is preferable to roll it up at a temperature of 00 to 710°C.

Then, it is cold rolled after being descaled by a conventional method and subjected to continuous annealing.

Continuous annealing allows the product to have a plate tensile strength of 42Kgf/- or less,
Any method can be used as long as the grain size number satisfies 8.5 to 11.5, but after performing recrystallization annealing for 5 seconds to 180 seconds at a temperature above the recrystallization temperature and below 850 ° C.
Cooled at a cooling rate of 250°C/sec, 250-500'
It is preferable to perform an overaging treatment at a temperature of C for 20 to IF 50 seconds, and the annealing conditions may be determined within the above range so as to obtain the characteristics of the product sheet.

Then, it is temper rolled in a conventional manner and subjected to a conventional surface treatment.

(Example) Table 1 shows examples of the present invention.

3. Steel having the components listed in Table 1 was bath-produced in a converter and continuously cast. Hot rolled to 1.0 inch, pickled, then cold rolled to 0.32 m, annealed under the annealing conditions listed in Table 1, then temper rolled to 1.0 inch, and electroplated. Ta. Similarly, Table 1 (-1) shows the crystal grain size and tensile strength of the electric tinned products manufactured under each condition.

Table 1 shows the total forming energy when the electric tinned steel sheet manufactured in this way was formed into a DI can using a DI processing machine in a laboratory. The smaller the total molding energy and the less occurrence of galling, the better the DI processability.

Furthermore, the pressure resistance and stretch flange processing rate of the DI cans were measured in a laboratory and the results are also shown in Table 1. It has been found that a stretch flange processing rate of 9.0% or more is determined to be acceptable by the customer in the case of the measurement method conducted by the present inventors' laboratory.

As can be seen from Table 1, the steel of the present invention has a small total forming energy, no galling, sufficiently high pressure resistance, extremely high stretch flanging rate, and particularly excellent stretch flanging formability.

On the other hand, for comparison steel, box annealed material (Nl113~14)
The total forming energy is small and there is no galling, but the elongation is 7.
Lunge processing rate and pressure resistance are poor. Box annealed material (Nal
5) has a grain size number outside the scope of the present invention, so the total forming energy is high and galling occurs.

Continuously annealed comparative steel No. 16 has a small total forming energy and does not cause galling, but has poor stretch flange formability because the grain size number is coarse, which is outside the scope of the present invention. Continuously annealed comparative steels NQ17-1B have high pressure resistance and excellent stretch flange formability, but their tensile strength is outside the scope of the present invention, so the total forming energy is high and galling occurs.

In addition, the steel of the present invention has not only high pressure strength due to BH hardening, but also
It should be added that since the buckling strength in the vertical direction of the can also increases, the buckling strength is also superior to that of box annealed materials if the material strength is the same. Furthermore, the steel of the present invention has particularly excellent elongation 7 flange formability, so it not only has a low defect rate in single elongation 7 lange processing, but also has a low cost that can withstand even more severe stretch flange processing, and has a uniform product material. To provide a steel sheet for DI cans that has excellent properties, is easy to perform DI processing without causing galling, has excellent stretch flange formability after DI processing, and has significantly improved pressure resistance by hardening during paint baking after DI processing. The industrial effect is enormous.

[Brief explanation of the drawing]

Figure 1 shows the tensile strength of the product plate, the total forming energy in the DI test forming machine, the compressive strength of the DI can that was subjected to post-forming paint baking treatment, and the annealing method for steel plates for DI cans manufactured on the actual manufacturing line. Figure 2 shows the relationship between the JIS grain size number, the compressive strength of the DI can, and the DI can steel plate manufactured on the actual manufacturing line.
FIG. 2 is a diagram showing the relationship between the processing rate until breakage occurs in stretch flange forming after processing and the annealing method. Figure 1 Tensile strength (kgf/mm)

Claims (1)

[Claims] C: 0.0040-0.0600% Mn: 0.05-0.50% P: 0.020% or less Liquid-soluble Al: 0.020-0.100% N : 0.0070% or less, with the remainder consisting of Fe and unavoidable impurities,
A steel sheet for DI cans with excellent stretch flange formability manufactured by continuous annealing and having a tensile strength of 42 Kgf/mm^2 or less and a grain structure with a JIS grain size number of 8.5 or more and 11.5 or less.