JP3369657B2 - High-strength and high-workability steel sheet for cans with excellent bake hardenability, aging resistance and non-earring properties, and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

This invention has high workability and bake hardenability, and therefore has extremely excellent can strength when used after can manufacturing and has little aging deterioration when stored at room temperature. The present invention also relates to a high-strength and high-workability steel sheet for can manufacturing, which has a property of causing less ears when drawn, that is, a non-earing property, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Materials for hard cans are, for example, Japanese Patent Publication No. 38-8563.
Generally, it is manufactured by a double cold rolling method as described in Japanese Patent Publication No. JP-A-2003-13898, and most of the hardening (strengthening) of the steel is carried out by so-called work strengthening. This is a method in which annealing is performed after primary cold rolling, and then cold reduction is applied until a target hardness is reached. Since this method is strengthened by processing, hardness (strength) is increased, but ductility is severely deteriorated and processing itself is difficult. Even if processing is possible, it is not reliable as a can. Met. Even in actual production, surface defects are likely to occur in the secondary cold rolling, which causes a problem such as a decrease in yield. This problem tends to increase with an increase in the rolling reduction in the secondary cold rolling. Furthermore, the strength of the strengthening method is essentially thermally unstable, which is also a problem.
For example, when the steel sheet is applied to a three-piece welding can or the like, the welding heat-affected zone (HAZ portion) tends to be softened, which is disadvantageous in that sufficient strength cannot be obtained at the joint.

On the other hand, for example, Japanese Patent Application Laid-Open No. 59-50125 discloses a method in which high temperature annealing is performed to increase the strength by utilizing a low temperature transformation structure. Since the occurrence of a layered structure due to uneven bending is unavoidable in this case, problems such as cracking occurred during the can manufacturing process and during use after can manufacturing. Further, in the combination of one-time high-pressure reduction cold rolling and low-temperature annealing, the in-plane anisotropy becomes large, which is an obstacle to use depending on the application.

In the can manufacturing process, it is indispensable to reduce the processing load at the time of molding, reduce tool wear, and improve shape fixability regardless of the type of can, so that the yield stress is low, so-called low yield. Ratio materials are required.

[0005]

SUMMARY OF THE INVENTION In summary of the above, it is important for a steel sheet for can making to have the following characteristics. The desired high strength can be obtained. It has good ductility. It has a low yield ratio. There is an increase in strength due to painting and baking. No material deterioration due to room temperature aging. Small in-plane anisotropy. Therefore, an object of the present invention is to provide a steel sheet for can making having the above-mentioned properties and an advantageous manufacturing method thereof.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned objects, the present inventors have studied positively utilizing two-phase zone annealing, which has not been used so far, and has investigated the composition of components, hot rolling, and cold rolling. It was found that the above properties can be secured by optimizing the rolling and annealing conditions.

That is, the present invention provides C: 0.08 to 0.15 wt.
%, Si: 0.10 wt% or less, Mn: 0.05 to 1.60 wt%, Al: 0.02
0 to 0.150 wt%, P: 0.015 to 0.150 wt%, S: 0.010
wt% or less and N: 0.0050 to 0.0120 wt%, the composition of the balance iron and unavoidable impurities, and the average particle size is 15
Bake hardenability, consisting of a mixed structure in which pearlite phase with an average grain size of 10 μm or less is uniformly dispersed in ferrite phase of μm or less, tensile strength: 50 kgf / mm ² or more and elongation: 5% or more A steel plate for cans with high strength and high workability, which has excellent aging resistance and non-earring characteristics. Here, the mixed structure may include bainite in a range of 5% or less.

Further, the present invention provides C: 0.08 to 0.15 wt%,
Si: 0.10wt% or less, Mn: 0.05-1.60wt%, Al: 0.020-
0.150 wt%, P: 0.015 to 0.150 wt%, S: 0.010 wt%
The steel material containing the following and N: 0.0050 to 0.0120 wt% is hot-rolled at a finishing temperature of 850 to 930 ℃, and then cooling is started at a cooling rate of 50 ℃ or more within 1 s and 540 ℃ or less 40
Winding in the temperature range of 0 ℃ or more, pickling, then reduction rate: 70 ~ 90
% Primary cold rolling, then (Ac ₁ + 10 ° C) ~
(Ac ₁ + 50 ° C) and keep it in the temperature range of 850 ° C or less for 20s or more to control the amount of austenite in the range of 10 to 50%, and then 400 ° C or less 300 ° C at a cooling rate of 70 ° C / s or more. After cooling to the above temperature range, and then maintaining the temperature range for 20 to 60 s, secondary cold rolling with a reduction rate of 10 to 35% is performed, and bake hardenability, aging resistance, non-resistance This is a method for producing a steel plate for cans having high strength and high workability, which is excellent in earring characteristics.

Further, in the present invention, the above steel plate or steel material further comprises Ni: 0.050 to 0.50 wt% and Cu: 0.050.
.About.0.50 wt% and B: 0.0005 to 0.0030 wt%.

[0010]

The reasons for limitation in the present invention will be described below in order from the component composition. C: 0.08 to 0.15 wt% 0.08 wt% to secure strength, more preferably 0.100 wt
% Or more is required. On the other hand, the upper limit is 0.15 wt% or less in consideration of weldability. The C content is preferably in accordance with the conditions for finally obtaining a suitable two-phase structure and its desired distribution form. In particular,
It is important to control the austenite phase ratio to be 10 to 50% during soaking during annealing, and the influence of the C content on this control is great.

Si: 0.10 wt% or less Si is an advantageous component for obtaining a two-phase structure, but it is 0.10 wt% or less in order to deteriorate the surface cleanability. The lower limit is about 0.01 wt%, but there is no major demerit due to further reduction. It should be decided in consideration of smelting technology.

Mn: 0.05 to 1.60 wt% Mn is necessary to obtain a finely dispersed structure in ordinary annealing, and in the ultra-thin steel sheet mainly targeted by the present invention,
Even with ordinary gas jet cooling, a relatively high cooling rate can be secured, so that a target fine dispersed structure can be obtained with a Mn content of about 0.05 wt%. On the other hand, if the content exceeds 1.60 wt%, in addition to the corrosion resistance of the steel sheet being deteriorated, the layered structure due to the cast segregation of Mn itself is not finally improved, and the cold rolling property is further reduced. Therefore, the upper limit was set to 1.60 wt%.

P: 0.015 to 0.150 wt% P is a desirable component in terms of material because it is effective for increasing strength and is inexpensive, but if it exceeds 0.150 wt%, the layered structure due to segregation is more likely to occur. To strengthen
It was set to 0.150 wt%. On the other hand, the lower limit is 0.015 wt, which is an effect of improving the material, taking into consideration the cost-increasing factors required for P removal.
%.

S: 0.010 wt% or less Since S causes deterioration of corrosion resistance in the can and promotes generation of a layered structure, it is desirable to reduce S. The effect of material improvement due to the reduction of S is more remarkable when the strength of the steel sheet is high. Therefore, in consideration of the S amount that reduces the above adverse effect and the cost increase due to the reduction of the S amount,
0.010 wt% or less, preferably 0.007 wt% or less.

Al: 0.020 to 0.150 wt% Al is contained as a deoxidizing agent in order to reduce inclusions.
Sufficient steel cleaning is achieved by the content of 020 wt% or more. However, an excessive content leads to abnormal hardening of the steel and the occurrence of surface defects, making it unsuitable for use as a steel sheet for cans, so the content should be 0.150 wt% or less.

N: 0.0050 to 0.0120 wt% N is used as a solid solution strengthening element, but when annealing is carried out in a low temperature region below the transformation point as in the conventional case, deterioration of aging becomes remarkable, and especially secondary cooling is performed. If the inter-rolling rate is low, its addition is limited. However, according to the manufacturing conditions according to the present invention, it was found that the material strength can be improved without causing remarkable deterioration of aging property, and it became possible to contain a large amount of N as compared with the conventional steel. Therefore, in order to obtain the target bake hardenability and high strength properties, N is 0.0050 wt%
It is necessary to contain the above. However, if it exceeds 0.0120 wt%, the bake hardening characteristics are improved, but the aging resistance tends to deteriorate, and it is difficult to control the components and it becomes a factor of material variation, so the upper limit is 0.0120 wt%. did.

Further, Ni, B and Cu all have the same effect in that the structure is made uniform and fine, and in the present invention, in addition to the above components, at least one of Ni, Cu and B is added. , Can be added in each range. Cu: 0.050 to 0.50 wt% Cu can strengthen the steel without hindering the ductility of the steel, and lowers the transformation point of the steel to relax the regulation of the hot rolling finish temperature, and to suppress the two phases during annealing. It has the effect of making area annealing easier. 0.05 for this effect to work
It is necessary to contain 0 wt% or more, but this effect is 0.50 wt%
If the content exceeds this range, the content will be saturated, and if the content exceeds that, the melting cost of steel will increase, so the range was set to 0.050 to 0.50 wt%.

Ni; 0.050 to 0.50 wt% Ni, like Cu, also has the effect of lowering the transformation point of the steel, and contributes to the improvement of the material through grain refinement of the structure.
For the same reason as Cu, the range of addition is regulated. Particularly, when the surface is required to be beautiful, it is desirable to add it in the range of 0.10 to 0.50 wt%. The effect of the addition of Ni can be similarly obtained in both the single addition and the composite addition with Cu.

B: 0.0005 to 0.0030 wt% B has a conventionally known effect of fixing N even when the coiling temperature in hot rolling is low. Is prevented from growing abnormally, and N is prevented from remaining in a solid solution state even when rapid cooling is performed after annealing to prevent aging deterioration of the material. 0.0005 wt% is necessary for exhibiting such an effect. On the other hand, if added excessively, the inner surface anisotropy of mechanical properties becomes large, so 0.0030 wt% or less is set. The effect of adding B is exhibited even when Ni and Cu are added simultaneously.

The steel sheet for a can according to the present invention has, in addition to the above component composition, a pearlite phase having an average particle size of 10 μm or less uniformly dispersed in a ferrite phase having an average particle size of 15 μm or less,
It is essential to have a mixed structure that is isolated and dispersed. That is, if the average grain size of the ferrite phase exceeds 15 μm, 2
In addition to the significant deterioration of the non-earring characteristics after the subsequent cold rolling, it becomes difficult to achieve both the important characteristics of the present invention, namely, improvement of the bake hardenability and aging resistance.
The cause of this is unknown, but it is considered to be based on a change in behavior of an interstitial solid solution element such as C segregated at the grain boundary. Further, the uniform and fine dispersion of pearlite also affects workability and aging characteristics. That is, when the average particle size of pearlite exceeds 10 μm, the workability is deteriorated, especially the local ductility is significantly deteriorated. Furthermore, in the mixed structure in which the pearlite phase is uniformly dispersed in the ferrite phase, it is important that the pearlite phase is isolatedly dispersed in the ferrite phase.
This is because if the pearlite phase is not dispersed in the ferrite phase in an isolated manner, the mechanical properties change discontinuously in the plate thickness direction, and the workability deteriorates. From the viewpoint of strength and workability, it is desirable that the second phase structure is only pearlite, but when bainite is mixed in for the purpose of improving strength, if the volume ratio is 5% or less, Material deterioration does not occur.

Next, the manufacturing conditions will be described for each step. 1) Hot rolling finishing temperature When the finishing temperature is less than 850 ° C, the layered structure develops, the workability deteriorates, and the uniformity of the material also deteriorates. On the other hand, when the finishing temperature exceeds 930 ° C, the structure of the mother plate becomes coarse and the structure of the final product also becomes coarse. Therefore, the finish rolling temperature was set to 850 ° C or higher and 930 ° C or lower.

2) Cooling condition If cooling is not started within 1 s after hot rolling, the structure becomes coarse, the strength of the final product is lowered, and the workability is deteriorated. Similarly, if the cooling rate is less than 50 ° C / s, it is not possible to obtain sufficient strength in the final product stage.
℃ / s or more.

3) Hot coiling temperature The coiling temperature in hot rolling also affects the strength and workability of the final product through the refinement of the mother plate structure. That is, by setting the winding temperature to 540 ° C. or less, a material having a uniform material and excellent strength and workability can be produced, but if the temperature is less than 400 ° C., the effect is almost saturated, but Due to operational problems such as deterioration of the coil shape, the hot coiling temperature was set to 540 ° C or lower and 400 ° C or higher.

4) Cold rolling reduction ratio By setting the reduction ratio in cold rolling to 70% or more, a fine and uniform structure can be obtained after annealing. On the other hand, if the rolling reduction exceeds 90%, the anisotropy of the mechanical properties of the steel sheet increases, so it is made 90% or less.

5) Annealing temperature and soaking time The annealing temperature is one of the important requirements of this invention, and (A
c₁+ 10 ° C) ~ (Ac ₁+ 50 ° C) and below 850 ° C
Hold for 20 s or more in the area and 10% of the amount of austenite during soaking
By setting it to ~ 50%, a uniform and fine group can be obtained after annealing.
The weave can evenly distribute the second phase. During soaking
To control the amount of austenite in the range of 10 to 50%,
It is important to control the soaking time as well as the blunt temperature,
Stable unless soaking time of at least 20 s or more
The material cannot be obtained, and the aging property varies greatly.

6) Cooling Rate After the above annealing, the material is cooled to a temperature range of 400 ° C. or lower and 300 ° C. or higher. The cooling rate in that case is important in controlling strength and aging. That is, by setting the cooling rate to 70 ° C./s or more, it is possible to increase the strength and obtain desirable bake hardening characteristics. The upper limit is not particularly limited, but there is no problem as long as it is within the range achieved by gas jet cooling.

7) Cooling Stop Temperature The cooling stop temperature is important for ensuring the bake hardenability, and the required amount of bake harden can be obtained by quenching to 400 ° C. or less. Although the detailed reason is not clear, it is presumed that the pearlite transformation during cooling can be suppressed by quenching to 400 ° C. or less.

8) Holding time in the temperature range of 300 ° C. or higher By holding the temperature in the temperature range of 300 ° C. or higher for an appropriate time after the quenching is stopped, the aging deterioration at room temperature can be achieved without significantly impairing the bake hardening amount. Can be suppressed. This suitable holding time is in the range of 20-60 s.

9) Secondary cold rolling rate The secondary cold rolling rate is an important condition for improving the strength and also important for preventing aging deterioration before working.
In other words, by applying a reduction of 10% or more, it is possible to almost completely prevent problems caused by the occurrence of stretcher strain during processing. Then, the desired mechanical characteristics can be obtained by adjusting the rolling reduction in the range of 10% or more.
However, when the rolling reduction exceeds 35%, the material strength improving effect of the secondary cold rolling is almost saturated, but on the other hand, the earring characteristics are deteriorated and the difficulty of the rolling operation itself is rapidly increased. Therefore, the secondary cold rolling rate is set to 10% or more and 35% or less.

[0030]

【Example】

Example 1 Steels having the chemical compositions shown in Table 1 were melted in a converter, hot-rolled, cold-rolled, and annealed under the conditions shown in Table 2, followed by 15% temper-rolling, and then temper rolling. Table 3 shows the results obtained by conducting a tin plating and examining the tensile properties, the bake hardening properties, and the aging resistance properties. However, J steel was manufactured by the conventional double cold rolling method for comparison. The secondary cold rolling rates were all 30%.

Here, the tensile properties were evaluated with JIS No. 5 test pieces. Similarly, the bake hardening characteristics were evaluated by using JIS No. 5 test pieces, after applying a 2% pre-strain, aging treatment at 210 ° C. × 20 min, and the increase in deformation stress before and after the aging treatment. The aging resistance was evaluated by the amount of elongation at yield when a tensile test was performed after strain-free aging treatment at 100 ° C for 30 minutes. This kind of steel sheet has a bake hardening amount (BH) of 5
kgf / mm ² or more, 2% occurrence of yield point elongation as aging resistance
It must be:

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

As is clear from the above results, it is understood that high strength and high ductility steel sheet can be obtained by subjecting the steel having the composition according to the present invention to predetermined thermomechanical treatment. Further, the invention steel has a large bake hardening property as compared with the conventional steel, but recovery of the yield point elongation after aging treatment is small, and excellent in aging resistance,
And it's clear that the earrings are small. Also,
No surface flaws harmful to the steel sheet for can making are generated. In the case of the invented steel sheet, the microstructures were different in volume ratio, but in all cases, it was desirable that pearlite was finely dispersed in fine ferrite ground. The average ferrite grain size of the invention steel sheet was 10 to 14 μm, and the average pearlite grain size was 5 to 9 μm.

Generally, so-called three-piece cans and two-piece cans are known as the types of cans, and various kinds of cans corresponding to commercially available 350 g cans are formed by using the steel sheet having the above mechanical properties. I conducted a survey. That is, i) Two-piece cans (DRD cans, DTR cans, DI cans) When drawing an invented steel sheet, the drawing is relatively shallow, but the ironing workability is equivalent to that of the conventional steel sheet. Various characteristics were obtained.・ Good ductility makes the drawing process of cans easier (with the invention steel sheet, the frequency of wrinkling during forming was reduced to about 80%). -The invention steel sheet has a low aging property, so the drawing process during can making is stable, and problems such as "waist break" do not occur during forming.・ Since the in-plane anisotropy is small, there are few ears during can making,
Yield is improved. -Low yield stress results in more uniform strain propagation throughout. -Since it has bake-hardenability, the strength of the final can itself is high.

Ii) Three-piece can-Inventive steel has a small aging property, so that the drawing process of the can is stabilized. -Low yield stress results in more uniform strain propagation throughout. -Since it has bake-hardenability, the strength of the final can itself is high.

As a comparative material, a material which has been work-hardened only by secondary cold rolling according to the conventional manufacturing method may undergo a sudden decrease in strength when subjected to heat treatment at a high temperature for a relatively long time. there were.

In the conventional secondary cold-rolled material (most of the strengthening depends on cold rolling), the variation of the material is large, and the final can strength is also a major cause of variation. It was However, in the invention steel sheet, it was revealed that the material control is easier because it is possible to provide a certain degree of strength after annealing and obtain a sufficient strength even if the secondary cold rolling rate is suppressed to a low level. .

Example 2 Using the steel A shown in Table 1, 2 was used under various conditions shown in Table 4.
5 # tinplate was manufactured and various investigations were conducted in the same manner as in Example 1. The results of the investigation are shown in Table 5. The secondary cold rolling rate was constant at 15%.

[0041]

[Table 4]

[0042]

[Table 5]

Example 3 Steels B (inventive steel) and J (comparative steel) shown in Table 1 were cold rolled and annealed under different conditions within the scope of the invention to adjust the strength. It was molded into a 250 ml beverage can, and its axial load resistance and can compressive strength were investigated. At that time, a baking coating treatment of 170 ° C. × 20 min was performed after molding. As shown in Table 6, the invention steel showed a final pressure resistance strength higher than that of the comparative material, although the strength of the original steel sheet was lower than that of the comparative material.

Here, the axial load resistance strength is the buckling strength when the can is axially compressed, and the can compression resistance strength is 12 mmφ and a 45 mm long cylinder is pressed against the can body to localize it. The pressure was applied, and the evaluation was made with a critical load that causes a depression.

[0045]

[Table 6]

The invention steel sheet is well adapted to the application of an organic resin film on the can surface (in this case, the surface treatment is preferably Cr plating instead of Sn), and particularly The invention steel sheet is excellent in that it is thermally stable, for example, in that the material is not deteriorated or changed by heat treatment during film attachment processing.

[0047]

According to the present invention, it is possible to provide a high-strength and high-workability steel sheet for cans which has high workability and bake hardenability, has little aging deterioration at room temperature, and has non-earring property. Therefore, it becomes possible to manufacture a product having extremely excellent can strength when used after can manufacturing.

Continuation of the front page (56) Reference JP-A-62-182225 (JP, A) JP-A-4-337049 (JP, A) JP-A-4-235250 (JP, A) JP-A-7-62487 (JP , A) JP 58-217659 (JP, A) JP 58-39736 (JP, A) JP 4-173946 (JP, A) JP 63-105932 (JP, A) JP 53-122612 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 8/02

Claims (5)

(57) [Claims] 1. C: 0.08 to 0.15 wt%, Si: 0.10 wt% or less, Mn: 0.05 to 1.60 wt%, Al: 0.020 to 0.150 wt%, P: 0.015 to 0.150 wt%, S: 0.010 wt% or less And N: 0.0050 to 0.0120 wt%, the balance is iron and inevitable impurities, and the pearlite phase having an average particle size of 10 μm or less is uniformly dispersed in a ferrite phase having an average particle size of 15 μm or less. A steel plate for cans with high strength and high workability, which has a mixed structure in a dispersed state, has a tensile strength of 50 kgf / mm ² or more and an elongation of 5% or more and is excellent in bake hardenability, aging resistance and non-earring characteristics. 2. The high-strength and high-workability steel sheet for can making according to claim 1, wherein the mixed structure contains bainite in an amount of 5% or less. 3. The steel sheet further comprises Ni: 0.050 to 0.50 wt%, C
The steel sheet according to claim 1 or 2, which has a component composition containing at least one of u: 0.050 to 0.50 wt% and B: 0.0005 to 0.0030 wt%. 4. C: 0.08 to 0.15 wt%, Si: 0.10 wt% or less, Mn: 0.05 to 1.60 wt%, Al: 0.020 to 0.150 wt%, P: 0.015 to 0.150 wt%, S: 0.010 wt% or less And N: 0.0050 to 0.0120 wt% steel material, finishing temperature:
After hot rolling at 850 to 930 ℃, start cooling at a cooling rate of 50 ℃ / s or more within 1 s, wind it in the temperature range of 540 ℃ or less and 400 ℃ or more, pickle it, and then reduce the rolling reduction: 70-90% of 1
Next cold rolling, then (Ac ₁ + 10 ℃) ~ (Ac ₁ +
(50 ℃) and keep it in the temperature range of 850 ℃ or below for 20s or more to control the amount of austenite in the range of 10 to 50%.
After cooling at a cooling rate of 70 ° C./s or more to a temperature range of 400 ° C. or less to 300 ° C. or more , and then maintaining the temperature range for 20 to 60 s, secondary cold rolling with a reduction rate of 10 to 35% is performed. The method for producing a steel sheet for cans having high strength and high workability, which is excellent in bake hardenability, aging resistance and non-earring characteristics. 5. The steel material further comprises Ni: 0.050 to 0.50 wt%,
The method for producing a steel plate for a high-strength and high-workability can according to claim 4, which contains at least one of Cu: 0.050 to 0.50 wt% and B: 0.0005 to 0.0030 wt%.