JPS63105932A - Manufacture of steel sheet for d&i can having superior flanging workability - Google Patents

Abstract

PURPOSE:To obtain a steel sheet for a D&I can having superior flange cracking resistance by subjecting a steel slab contg. specified amounts of C, Si, Mn, Al and N to hot rolling, cold rolling and box annealing under controlled temp. conditions. CONSTITUTION:A steel consisting of, by weight, 0.001-0.10% C, <=0.10% Si, <=0.50% Mn, <=0.06% Al, <=0.003% N and the balance Fe with inevitable impurities or further contg. 0.015-0.08% Cr is manufactured by refining and cast into a slab. This slab is hot rolled at a finishing temp. of the Ar3 transformation point or above, coiled at 500-650 deg.C, cold rolled at 80-95% draft and box- annealed at the recrystallization temp. - the Ac1 point. By this method, a steel sheet for a D&I can having well-balanced drawability, ironability and flanging workability is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to drawing and ironing.
ng), i.e. D&I cans (Draw & Ir.
The present invention relates to a method for producing a thin steel sheet for D&I cans that has excellent workability, especially flange workability.

(Prior art) Thin cylindrical cans, such as food cans, have traditionally been manufactured as three-piece cans with an upper and lower lid attached to a soldered or welded body, but in recent years, with the development of can manufacturing technology, Due to the cost of can-making steel sheets, lead pollution countermeasures, and consumer preferences, D&I cans are increasingly being used for so-called internal pressure cans, such as beer cans and carbonated soft drink cans, where the internal pressure is higher than atmospheric pressure. ing.

This D&I can is made of cup (Cu) by deep drawing process.
P) is molded and then ironed to pass through several stages of dies with an inner diameter smaller than the outer diameter of the cup, thereby reducing the can wall thickness and increasing the height, so that the seamless body and bottom are integrated. It is a two-piece can.

This is a can manufacturing technology that was originally developed using aluminum as a material, but due to the higher quality of tinplate (high workability, formability, and uniform thickness) and the advantages of being a low-cost material, steel has been replaced with aluminum. is making great progress. Along with this movement, the development of materials for DkI steel with good workability, such as Al
D with improved ironing properties by adding boron to killed steel
Further improvements are being made, such as the &I steel plate for cans being proposed in Japanese Patent Publication No. 57-51448.

What are the advantages of two-piece cans compared to traditional three-piece cans?

(1) Can walls can be made thinner due to increased strength through processing.

(2) Light weight and low material cost.

(3) No soldering or welding required.

(4) Entire printing on the body is possible.

It is expected that they will be used more and more in beverage cans in the future.

(Problem to be solved by the invention) Currently, A1 killed continuous cast steel sheet is generally used as a material for producing steel D&I cans on an economical scale, but this is not suitable for deep drawing of automobile outer panels, etc. It is manufactured using the same method as the steel plate used. The crystals in steel sheets have a pancake-like shape with a large grain size and a high γ value, so they are said to be suitable for &I processing such as drawing and ironing, but the larger the grain size is, the worse the stretch flangeability is. This makes it a disadvantageous material in terms of securing secondary molding processability.

For this reason, current materials still have a material problem in that they have a higher rate of flange cracking than aluminum during flange processing to attach can lids after D&I processing.

This cracking caused by flange processing is due to the severe processing history that the can wall has undergone, but it has a large impact on operational problems on continuous can manufacturing lines such as D&I can manufacturing and quality deterioration due to leakage of can contents. Therefore, even an extremely small cracking rate of about 150 ppm is becoming a problem.

The main cause of flange cracking is coarse nonmetallic inclusions, so empirically, attempts have been made to reduce the incidence of cracking mainly by improving the cleanliness of the steel. The actual situation is that flange cracking cannot be sufficiently prevented because the secondary molding processability of the material itself is poor.

(Means for Solving the Problems) The present inventors conducted numerous experiments and studies in order to develop a new thin steel sheet for D&I cans that compensates for the shortcomings of the materials currently used as thin steel sheets for D&I cans and takes advantage of their strengths. As a result,
This new method of manufacturing a thin steel plate for cans has excellent D& processability such as drawability and ironing property, particularly excellent flange cracking resistance, and low production cost of the steel plate.

The present invention will be explained in detail below.

In the structure of the present invention, the chemical composition of the steel piece is [C] 0.
001-0.1%, (Si) 0.10% or less, (Mn
) is 0.50% or less, (Al) is 0.06% or less, (C
r) is 0.015 to 0.08% as required, (N) is 0.003% or less, and the balance is iron and unavoidable impurities.

If (C) is contained in an amount greater than 0.10%, the D&I processability deteriorates due to an increase in hardness. In addition, reducing the content to less than 0,001% is accompanied by difficulties in melting and high costs in a general industrial-scale steelmaking furnace.

(Si) hardens steel and reduces workability, but 0.10
The upper limit is set at 0.1% as it does not significantly reduce the workability.
0%.

(Mn) also hardens steel and reduces workability, but 0.50
% or less does not affect the processability of D&I cans.

[AI] only needs to be in the amount necessary to deoxidize the steel, and if it exceeds an appropriate amount, it will deteriorate the cleanliness of the steel and further increase the cost, so the upper limit is set at 0.06%.

(Cr) uses box annealing as a manufacturing requirement of the present invention, so the purpose is to prevent carbon contamination during annealing, refine grains and carbides by adding Cr, and control ^IN precipitation by Cr nitrides. It is added in an amount of 0.015 to 0.08% in order to improve flange workability, and it is preferable to add it as necessary considering the conditions during manufacturing.C
When adding r, if the amount is less than o, ois%, no effect will be observed, and if the amount is too large, the steel will be hardened, so the upper limit is set to 0.08%.

(N) is one of the basic requirements of the present invention. That is, the present inventors have discovered that when (N) is reduced to 0.003% or less in Al-killed steel, the overall can-making properties as a material for D&I cans are dramatically improved.

In conventional D&I can materials, crystal grains have been made larger in a pancake shape to improve drawability and ironing properties, but on the other hand, there are contradictory requirements for making crystal grains smaller in order to improve stretch flangeability. It has been demanded.

The present inventors focused on improving the accuracy rate of nitrogen blending in steelmaking, and conducted a detailed study on the relationship between nitrogen content and crystal structure, which had not been given much attention so far, and reduced the N content to 0.00.
By controlling the amount of nitrogen at 4% or less (40ppm or less), the degree of elongation (axial ratio) of the crystal grains can be adjusted by changing the amount of nitrogen to change the shape of the crystal grains from pancake-like to spherical, as shown in Figure 1. found out that it is possible. Furthermore, 0.0 nitrogen
By controlling it to 0.3% or less, the drawability and Ir
This is a newly established technology for manufacturing steel sheets for D&I cans that achieves a well-balanced balance between oning properties and flanging properties and improves the overall can-making properties required as a material for D&I cans.

It is preferable that the unavoidable components of S and P are as small as possible, and S is 0.0
It is desirable that P be 25% or less, and P be 0.020% or less.

This steel may be melted in a converter, electric furnace, or any other melting furnace, and is preferably continuously cast into a slab after taking measures to reduce inclusions.

Once the slab is cooled, or as a hot piece, it is 1000~1
After loading the slab into a soaking furnace at 400°C, hot rolling is carried out.In hot rolling, Ar is preferably above the transformation point from the viewpoint of can-making processability, and the coil winding temperature is determined to ensure descaling of the hot-rolled coil. The upper limit is set to 650°C in consideration of the agglomeration of carbides,
If the winding temperature is too low, the crystal grains will become fine and the hardness will increase, and the shape of the steel strip will be poor and the material will vary due to uneven cooling, so it is desirable to set the lower limit to 500°C.

Further, pickling and cold rolling are performed, and the cold rolling reduction ratio is required to be in the range of 80 to 95%, especially from the viewpoint of suppressing the formation of ears after cup forming.

Annealing should be box annealing, and either tight coil method or open coil method may be used.The temperature raising method may be the most economical condition according to the performance of the annealing furnace.The annealing temperature should be above the recrystallization temperature and below the AC process temperature. If it is less than that, the can manufacturing processability will be poor.
On the other hand, if the temperature becomes too high, it will cause seizure of the coil and formation of large lumps of carbide, so it is set to Ac1 or less.

After annealing, temper rolling is performed at a rolling reduction of 5% or less, if necessary.

The steel sheet according to the present invention is manufactured through the above-mentioned process, and after surface conditioning such as degreasing and pickling, metal plating such as tin plating, chemical conversion treatment such as phosphate treatment, and coating with organic matter such as painting can be performed according to the purpose of the can. After surface treatment, it is used as steel plate for D&I cans.

(Example) Examples of the present invention will be described below.

After melting steel having the components shown in Table 1 in a converter, continuous casting was performed. These steels were hot rolled, cold rolled and annealed under the conditions shown in Table 2, skin bath rolled at a rolling reduction of 1.3%, and then tin plated on a normal electroplating line. The comparative material is the current steel plate for D&I cans.

The mechanical properties of the tin-plated steel sheet produced by this process are shown in Table 3, along with a conventional D&I can steel sheet (with pancake-shaped grains) for comparison. Furthermore, regarding the stretch flange formability of the present invention material after D&I processing, Iro
The cans after ning were evaluated by the cone test method, and the results are shown in FIG.

The cone test method is as shown in Figure 3, where a can-shaped opening cone is placed at the opening of an ironing can at a rate of 500 mm/+min.
This method measures the stroke length until cracking occurs at the pressing opening at a speed of The larger the stroke length, the better the flange cracking resistance and the better the secondary forming processability.

(Effects of the Invention) As is clear from the results shown in FIG. 2, the material of the present invention has a longer crushing stroke length than the comparative material, and has excellent flange cracking resistance.

Moreover, it has extremely excellent secondary molding processability.

Users have also been able to use the material without any problem in making cans, and these results demonstrate that the material of the present invention is a material for D&I cans that is superior to the current material for D&I cans.

3.Make-up・

[Brief explanation of the drawing]

FIG. 1 shows the relationship between the Total (N) amount and the degree of elongation, which is a basic requirement of the present invention. FIG. 2 is a diagram showing the test results of the stretch flange formability of the present invention material and the comparative material in the example of the present invention using the contest method. FIG. 3 is a schematic diagram of the cone test situation. The can size used was a 202 diameter D&I can.

Claims (2)

[Claims] (1) C: 0.001-0.10%, Si as weight%
: 0.10% or less, Mn: 0.50% or less, Al: 0.
A steel billet consisting of 0.06% or less, N: 0.003% or less, the balance iron and unavoidable impurities is hot rolled to a temperature of Ar_3 transformation point or higher, rolled at 500°C or higher and 650°C or lower, then rolled at 80°C.
Ac
A method for manufacturing a steel plate for D&I cans with excellent flange workability, characterized by box annealing at a temperature of _1 or less. (2) C: 0.001-0.10%, Si as weight%
: 0.10% or less, Mn: 0.50% or less, Al: 0.
06% or less, Cr: 0.015-0.08%, N: 0.
A steel billet consisting of 0.003% or less, the balance iron and unavoidable impurities is hot rolled to a temperature of Ar_3 transformation point or higher, rolled at a temperature of 500°C or more and 650°C or less, and then cold rolled at a reduction rate of 80 to 95%, A method for producing a steel sheet for D&I cans having excellent flange workability, characterized by box annealing at Ac_1 above the recrystallization temperature.