JPH0478714B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to a steel plate for DI cans (Draw & Ironed Cans), which has excellent stretch flange formability after DI processing, is easy to perform DI processing, and hardens during paint baking after DI processing. Compressive strength is improved by
This relates to steel plates for DI cans. (Prior Art) Surface-treated steel sheets, such as tin-plated steel sheets or tin-free steel sheets treated with chromic acid, are often used for food cans, aerosol cans, and easy-open 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 & Ironing processing, i.e., ironing processing is performed after deep drawing processing). is also increasingly required. The manufacturing process for DI cans involves shallow drawing a steel plate using a punch and die to form a cup, and then drawing the side wall using a punch and die with a clearance smaller than the thickness of the side wall of the cup. Container (cup) of predetermined depth by decreasing
After that, a flange process is performed to wrap the lid around the end of the cup. The characteristics required for steel sheets for DI cans are:
It is required to have good workability during DI processing, no galling, low processing energy, and high pressure resistance as a can body. Conventionally, materials for such DI cans have been box-annealed, for example, B-added Al-killed steel (Japanese Patent Application Laid-Open No. 53
-48913) and box-annealed Cu-added low carbon steel (Special Publication No. 52-16965). This is because box-annealed materials have better elongation and deep drawability, and are generally considered suitable for DI processing applications. In particular, good stretch flange formability is extremely important in the molding process of DI cans, and the defective rate must be kept to a few tens of ppm or less. For this reason, box-annealed materials that elongate as steel plates and have excellent r-values have traditionally been used. (Problems to be Solved by the Invention) On the other hand, in recent years, the plate thickness of DI cans has become increasingly thinner, and the demand for increased pressure resistance has become extremely strong. The pressure resistance of the can body is determined by (plate thickness) ² × (strength),
To make it thinner, it is necessary to increase the strength of the material, but
Box annealed materials are generally soft, making it difficult to make them thinner. In order to improve the strength, it is necessary to add reinforcing elements to make it a relatively high-alloy component, and in this case there is a problem that DI workability deteriorates. Furthermore, increasing the strength of the steel sheet has the disadvantage that galling is more likely to occur during DI processing, and processing energy also increases. Recently, manufacturing steel sheets for DI cans by continuous annealing has been considered, but it has not been possible to prevent the occurrence of small cracks in flange forming during DI processing, and galling has also been observed here and there. . The purpose of the present invention is to have excellent stretch flange formability,
To provide a container material for DI cans that does not cause galling, is easy to process through DI, and has high pressure resistance after DI processing. (Means for Solving the Problems) As a result of various studies on various characteristics required for DI cans, the present inventors found that regarding steel sheets for DI cans,
Considering the DI formability and the practical properties of DI cans,
Rather than box annealing material, the strength, grain size,
The present invention was completed based on the new finding that a continuously annealed material with a specified precipitate size is superior. 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 contrary to conventional knowledge. The tensile strength of the steel plate is 42Kgf/ ^mm2 or less, the grain size number is 8.5-11.5, 0.02μm or more and 0.40μ
MnS with an average size of less than m and 0.005μm or more
It has an AlN precipitate structure with an average size of 0.20 μm or less, C: 0.0040 to 0.0600%, Mn: 0.05 to 0.50%,
P: 0.02% or less, S: 0.015% or less, acid-soluble Al:
0.020-0.100%, N: 0.0070% or less, however,
Continuously annealed steel material having a relationship between [Mn weight %] and [P weight %] as follows: 10 [P weight %] - 0.03 ≦ [Mn weight %] ≦ 20 [P weight %] + 0.14 It was newly discovered that the stretch flange formability after DI processing is excellent despite having solid solution C. The present inventors have discovered that in this continuous annealing 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 is also increased (hereinafter this property is referred to as BH property). found out. In other words, by using the continuously annealed material, which is softer than the box annealed material, it is soft during DI processing, and therefore has excellent DI workability, and has the excellent characteristics that the pressure resistance after painting is baked is higher than that of the box annealed material. 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, and 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 causing galling, so the upper limit is set at 42 Kgf/mm ² . A preferred range is a tensile strength of 40 Kgf/mm ² or less. Figure 1 shows C: 0.0040~0.080%, Mn: 0.15~
0.60%, P: 0.006-0.030%, S: 0.005-0.015
%, acid-soluble Al: 0.005 to 0.070%, N: 0.0070% or less steel was melted in a vacuum melting furnace and manufactured on a laboratory pilot line. Tensile strength and DI test forming of the product sheet. The relationship between the total forming energy in the machine and the pressure resistance strength of DI cans subjected to post-forming paint baking treatment is shown in relation to the annealing method. As you can see from Figure 1, the tensile strength is 42Kgf/mm ²
If it exceeds , the total forming energy increases significantly and galling occurs frequently, making DI processing difficult. In order to keep the total forming energy stable and low,
It is preferable that the tensile strength is 40 Kgf/mm ² or less, the yield point is 36 Kgf/mm ² or less, more preferably the tensile strength is 37 Kgf/mm ² or less, and the yield point is 30 Kgf/mm ² or less. Further, the compressive strength increases as the tensile strength increases, and the compressive strength of continuously annealed material is about 1 to 2 kgf/cm ² higher than that of box annealed material even if the tensile strength is the same. In order to ensure such BH properties, the amount of solid solute C in the steel sheet is
It is preferable to contain 5.0 ppm or more. Next, crystal grain size will be explained. Figure 2 shows C: 0.0044~0.076%, Mn: 0.16~
0.57%, P: 0.008-0.030%, S: 0.005-0.015
%, acid soluble Al: 0.007~0.080%, N: 0.0020~
JIS grain size number, processing rate until breakage occurs in stretch flange forming after DI processing, and pressure resistance for steel plates for DI processing made by melting steel with a content of 0.0070% or less in a vacuum melting furnace and manufactured on a laboratory pilot line. The relationship is shown 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 by the customer using the measurement method conducted by the present inventors in the laboratory. As can be seen from Figure 2, the stretch flange processing rate increases as the grain becomes finer (the larger the grain size number).
In order to improve the stretch flange processing rate and ensure a stretch flange processing rate of 9.0% or higher, in the case of continuously annealed materials, a grain size number of 8.5 or higher 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, as the grain size becomes finer, the stretch flange formability and pressure resistance improve, but the steel becomes harder, and if the grain size number exceeds 11.5, the total forming energy during DI processing increases significantly, causing galling.
DI processing becomes difficult. Therefore, the grain size number is specified as 8.5 to 11.5. Preferably range 9.0~
It is number 11.0. Next, the dimensions of the precipitates on the steel plate will be explained. Figure 3 shows C: 0.021-0.045%, Mn: 0.16-0.30
%, S: 0.005-0.04%, P: 0.008-0.017%, acid-soluble Al: 0.005-0.100%, N: 0.0010-0.0070%
Steel is melted in a vacuum melting furnace and heat treated under various conditions before hot rolling and after hot rolling.
The average size of MnS and AlN precipitates and the stretch flange after DI processing determined from a huge number of electron micrographs of steel sheets for DI processing manufactured on a laboratory pilot line by varying the size of MnS and AlN precipitates. The relationship between the processing rate until breakage occurs during molding is shown. The numbers in the figure represent the stretch flanging rate of a sample having a precipitate structure with the average size of MnS and AlN at that point, and the curves represent the contour lines of the stretch flanging rate. As can be seen from Figure 3, the average precipitate size of MnS is less than 0.02 μm or more than 0.40 μm, or AlN
The average precipitate size is less than 0.005μm or 0.20μm
If it exceeds the limit, the stretch flange processing rate will deteriorate. Therefore, the average precipitate size of MnS is 0.02 μm or more and 0.40 μm.
m or less, the average precipitate size of AlN is 0.005 μm or more,
Specify 0.20μm or less. Next, the steel components will be explained. Since C hardens steel, its upper limit is set at 0.0600%. Reducing the C content is effective for softening, but if the C content is reduced to less than 0.0040%, the solid solution C will decrease significantly and BH properties cannot be obtained, so the lower limit should be set to 0.0040%.
%. The preferred range is 0.0040-0.0400%. Mn is 0.05% to prevent hot embrittlement caused by S.
It is necessary to contain more than 0.5%, 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 0.10-0.30%. At least acid-soluble Al It is necessary to contain 0.020%. However, if it exceeds 0.100%, it will harden the steel and increase surface flaws. The preferred range is 0.030-0.080%. Both P and N are elements that significantly harden steel, and by lowering both P and N, a more pronounced softening effect than previously thought can be obtained. In order to obtain the specific steel plate for DI cans of the present invention,
The upper limit of P is 0.020% and the upper limit of N is 0.0070%.
The preferred range of N is 0.0030% or less. Moreover, Mn and P have a special interaction regarding stretch flange formability, and even if the content of each is within the above range, the amount of Mn and P may be unbalanced compared to the other amount. It was found that stretch flange formability deteriorated. As a result of finding a regression equation through experiments, we found that in order to stably ensure good stretch flange formability, the content of Mn and P should be 10 [P weight %] - 0.03 ≦ [Mn weight %] ≦ 20 [ P weight %] +0.14 The following relationship needs to hold true. Especially tensile strength 37Kgf/mm ² or less, yield point 30Kgf/mm ²
When manufacturing the following softer steel sheets with excellent DI workability, C: 0.0040~0.0400%, Mn: 0.10~
0.25%, acid soluble Al: 0.030-0.080%, P: 0.015%
Hereinafter, it is preferable that S: 0.015% or less and N: 0.0025% or less. S becomes inclusions in steel and causes surface defects in steel sheets, cracks during processing, stretch flange cracks, and the formation of MnS with an excessively large average precipitate size, so the upper limit is set at 0.015%. The steel components in the present invention are as described above,
If necessary, it is also possible to further add one or two of carbonitride-forming elements B of 0.0050% or less and Cr of 0.10% or less to the steel components of the present invention. By adding these elements
Steel plates with excellent DI workability can be stably produced. The manufacturing method of the present invention will be described. The steel having the above-mentioned specific components is melted by a conventional method, made into a steel billet by a continuous casting method or an ingot-forming and blooming rolling method, and then subjected to hot rolling. The heat treatment conditions for the steel billet prior to hot rolling may be any conventional method. In other words, hot pieces may be sent directly and rolled.
It may be reheated in a heating furnace. In order to produce steel sheets for DI cans that are particularly soft and have excellent DI workability and stretch-flange formability, continuous casting is used to form steel billets, and Ar ₃
After cooling to below the transformation point, T*=6875/(3.865−log[Al%+0.015])−
It is preferable to reheat the product to a temperature range below T*°C that satisfies 250° C. and then subject it to hot rolling. The hot rolling may be carried out by any conventional method, but it is preferable to roll it up at a temperature of 600 to 710°C. Then, it is descaled and cold rolled in the usual manner,
Subjected to continuous annealing. Continuous annealing can be carried out by any method as long as the tensile strength of the product plate is 42Kgf/ ^mm2 or less and the grain size number is 8.5 to 11.5, but recrystallization annealing is recommended at a temperature above the recrystallization temperature and below 850℃ for 5 seconds to 180 seconds. After that, it is cooled at a cooling rate of 5 to 250℃/second, and
It is preferable to perform an overaging treatment at a temperature of 500° C. for 30 to 180 seconds, and the annealing conditions may be determined within the above range so as to satisfy 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. Smelting steel having the components listed in Table 1 in a converter,
Continuously cast steel slabs were hot rolled to 3.0 mm, pickled, then cold rolled to 0.32 mm, annealed under the annealing conditions listed in Table 1, and then temper rolled to 1.0%. I went sparrow hunting. Similarly, Table 1 shows the crystal grain size and tensile strength of the electric tinned product sheets 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 forming energy is, the less galling occurs.
Indicates excellent DI processability. Furthermore, the results of laboratory measurements of the compressive strength and stretch flange processing rate of the DI can are also shown in Table 1. It has been found that a stretch flange processing rate of 9.0% or more is evaluated as acceptable by the customer using the measurement method conducted by the present inventors in the laboratory. As can be seen from Table 1, the steel of the present invention has a small total forming energy, no galling, sufficiently high compressive strength, extremely high stretch flanging rate, and excellent stretch flanging formability.
On the other hand, regarding the comparative steels, the box-annealed materials (Nos. 13 to 14) have a small total forming energy and do not cause galling, but are inferior in stretch flange processing rate and compressive strength.
Since the box annealed material (No. 15) has a grain size number outside the scope of the present invention, 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 Nos. 17 and 18 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. Continuously annealed comparative steel No.
Samples Nos. 19 to 20 have a balance of Mn and P contents outside the scope of the present invention, and therefore have slightly poor stretch flange formability. Comparative steel continuously annealed materials No. 21 to 24 are MnS and AlN.
Since the average size of the precipitates is outside the scope of the present invention, the stretch flange formability is extremely poor. In addition, the steel of the present invention increases not only the pressure strength but also the buckling strength in the vertical direction of the can due to BH hardening, so it has superior buckling strength compared to box annealed steel if the material strength is the same. I would like to add this. Furthermore, since the steel of the present invention has particularly excellent stretch-flange formability, it not only has a low defect rate in stretch-flange forming, but also has the ability to withstand even more severe stretch-flange forming.

【table】

【table】

[Table] (Effects of the invention) The present invention can be manufactured by continuous annealing, resulting in low manufacturing costs, excellent uniformity of product material, no galling, easy DI processing, and elongation after DI processing. The present invention provides a steel plate for DI cans that has excellent flange formability and significantly improves pressure resistance by hardening during paint baking after DI processing, and its industrial effects are enormous.

[Brief explanation of drawings]

Figure 1 shows the tensile strength and DI of steel sheets for DI cans manufactured on a laboratory pilot line.
Figure 2 shows the relationship among the total forming energy in the test forming machine, the compressive strength of DI cans that were subjected to post-forming paint baking treatment, and the annealing method. Figure 2 shows the steel plate for DI cans manufactured on the laboratory pilot line. Figure 3 shows the relationship between the JIS grain size number, the compressive strength of the DI can, the processing rate until breakage occurs during stretch flange forming after DI processing, and the annealing method. FIG. 2 is a diagram showing the relationship between dimensions, average size of AlN precipitates, and processing rate until breakage occurs in stretch flange forming after DI processing.

Claims (1)

[Claims] 1% by weight: C: 0.0040-0.0600% Mn: 0.05-0.50% P: 0.02% or less S: 0.015% or less Acid-soluble Al: 0.020-0.100% N: 0.0070% or less, however, [ There is a relationship between Mn weight %] and MnS has a component consisting of impurities, has a tensile strength of 42Kgf/mm2 ^or less, a grain structure with a JIS grain size number of 8.5 or more and 11.5 or less, an average size of 0.02μm or more and 0.40μm or less, and an average size of 0.005μm or more and 0.20μm or less. AlN
A steel plate for DI cans with excellent stretch flange formability manufactured by continuous annealing and having a precipitate structure.