JPH05271780A - Manufacture of nonaging extra thin steel sheet for soft vessel by continuous annealing - Google Patents

Abstract

PURPOSE:To manufacture a steel sheet for a soft vessel having <=3T refining degree and having nonaging properties equal to those of a batch-annealed steel sheet by a continuous annealing furnace. CONSTITUTION:A hot steel slab constituted of <=0.0015% C, 0.05 to 0.40% Mn, <=0.06% P, 0.01 to 0.10% acid soluble Al and <=0.0060% N is once cooled to <=950 deg.C, is thereafter reheated to 1000 to 1200 deg.C and is hot-rolled at >=850 deg.C finishing temp. Within 1.5sec after the discharging of the hot rolled steel strip from a finish final stand of a hot rolling mill, while cooling is executed on a run-out-table, it is coiled at 650 to 750 deg.C, is subjected to cold rolling, is annealed by a continuous annealing furnace and is subsequently subjected to skinpass rolling at 0.6 to 10% elongation percentage. In this way, the objective extra thin nonaging steel sheet of <=0.3mm can industrially be manufactured at a high speed of >=300m per minute by a continuous annealing furnace without executing averaging treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an ultra-thin steel sheet for a soft container, which has a temper of T-3 or less and has a nonaging property equivalent to that of a batch annealed steel sheet by a continuous annealing method.

[0002]

2. Description of the Related Art There are a batch annealing method and a continuous annealing method as an annealing method in the manufacturing process of a steel sheet for containers. The continuous annealing method has a better shape than the batch annealing method, has uniform mechanical properties in the width and longitudinal directions of the steel strip, and has the advantage of high productivity, but has the problem that it is difficult to manufacture soft steel sheets. .. Therefore, conventionally, a steel sheet for a soft container having a temper of T-3 or less is manufactured by a batch annealing method, and a steel sheet for a hard container having a T-4 or more is mainly manufactured by a continuous annealing method.

However, in recent years, can makers are in a trend of demanding cans that are more difficult to process, such as ironing, from the market. Therefore, the demand for steel sheets for soft containers having a temper of T-3 or less is important. It's getting higher. On the other hand, in order to improve the yield and quality of can makers, container steel sheet manufacturers are strongly required to supply container steel sheets with better shape and uniform width and longitudinal mechanical properties of steel strip. Became.

Therefore, in recent years, a method for producing a steel sheet for a soft container having a temper of T-3 or less by continuous annealing has been developed. For example, Japanese Patent Publication No. 63-10213 discloses that
A method for producing a low carbon aluminum killed steel sheet for a soft container using a continuous annealing furnace with overaging treatment has been developed.

However, the low carbon aluminum killed steel sheet for soft containers produced as described above has a problem that the non-aging property similar to the batch annealed steel sheet cannot be obtained. That is, in a low carbon aluminum killed steel container steel sheet manufactured using a batch annealing furnace, solid solution C that causes an aging phenomenon precipitates as a carbide during the slow cooling process of batch annealing, and another aging phenomenon occurs. Since solute N is precipitated as aluminum nitride during the hot rolling and batch annealing processes, neither solute C nor solute N are present, and complete non-aging is exhibited.
However, it is thermodynamically impractical to reduce the amount of solid solution C to be equal to or less than the equilibrium solid solution amount at the overaging treatment temperature in the steel sheet for a container of low carbon aluminum killed steel manufactured using a continuous annealing furnace with overaging treatment. Since it is possible, some amount of solid solution C remains in the product, and some aging property is exhibited.

Therefore, the low carbon aluminum killed steel container steel sheet produced by using the continuous annealing furnace with the overaging treatment has a drawback that the aging phenomenon progresses in the coating and baking process in the can making industry, which causes hardening and deterioration of workability. there were. The workability deterioration referred to here is a phenomenon in which a waist bend called fluting is generated in a cylindrical bending process, and a wrinkle called a stretcher strain is generated in an overhang process. All of these workability deteriorations are a kind of plastic instability phenomenon, and the mobile dislocations introduced by temper rolling are fixed to solid solution C and solid solution N as the aging progresses, and the yield point elongation in the tensile test is increased. Is due to recovery.

[0007] In recent years, from the viewpoint of resource saving, can makers are increasingly demanding steel sheet manufacturers for containers to use thinner steel sheets with a thickness of 0.3 mm or less, but with continuous overaging treatment. Since the annealing furnace has a long path length and it is difficult to finely control the steel strip tension in the furnace, it has been difficult to efficiently manufacture a thin steel sheet for soft containers at high speed. In addition, in the production of steel sheets for low carbon aluminum killed steel containers using a continuous annealing furnace with overaging treatment, it is necessary to provide a long overageing treatment zone in the continuous annealing furnace, so there is a need for equipment costs and variable costs such as fuel and electricity. There were also problems such as an increase and a decrease in productivity.

As a production method for overcoming these drawbacks, for example, as disclosed in Japanese Patent Application Laid-Open No. 58-197224, a carbide-forming element such as niobium or titanium is added to a steel component so that solid solution C is stable carbide. As such, a method of completely precipitating by the end stage of hot rolling has been developed. However, since this method also requires expensive alloying elements such as niobium and titanium, the material cost is high, and since these alloying elements raise the recrystallization temperature, high-temperature annealing must be performed, and thin alloys are required. There is a problem that the steel strip cannot be efficiently annealed at high speed.

[0009]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks and problems, and even in a continuous annealing furnace without overaging treatment,
An object of the present invention is to provide a method capable of producing an ultra-thin steel sheet for a soft container having a temper of T-3 or less and having a nonaging property equivalent to that of a batch annealed steel sheet.

[0010]

In order to achieve the above-mentioned object, the present inventors have studied in detail the steel composition and hot rolling conditions, and as a result, have properly controlled the steel composition, especially C
Special elements such as niobium and titanium are added by combining the content reduction to the limit and controlling the cooling start time at the run-out table after finishing rolling especially under hot rolling conditions. It was found that the steel sheet for the above purpose can be manufactured without doing so.

The present invention is constructed on the basis of this finding. The gist of the present invention is that C: 0.0015% or less by weight%, Mn: 0.05-.
0.40%, P: 0.06% or less, S: 0.06%
Hereinafter, acid-soluble Al: 0.01 to 0.10%, N: 0.006
A hot steel slab containing 0% or less and the balance of iron and unavoidable impurities is once cooled to 950 ° C or less, then reheated to a temperature of 1000 to 1200 ° C, and hot-rolled at a finishing temperature of 850 ° C or more. While being cooled on the run-out table within 1.5 seconds after the hot-rolled steel strip exits the finishing stand of the hot-rolling mill, it is wound at a temperature of 650 to 750 ° C., pickled, Cold rolled, annealed in continuous annealing furnace, then 0.6
It is a method for producing an ultra-thin steel sheet for soft non-aging containers that is temper-rolled at an elongation of 10%.

The present invention will be described in detail below. First, the reasons for limiting the steel components of the present invention will be described. The C content is the most important constituent element of the present invention. C is an element that causes aging, and it is necessary to reduce it as much as possible for the purpose of the steel sheet for a non-aging soft container of the present invention. However, it is impossible to reduce the C content to 0 by an industrial steel melting method.

[0013] Therefore, the present inventors have studied the limit C content which is allowable in producing a non-aging soft steel sheet. As a result, if the C content exceeds 0.0015%, the product annealed in the continuous annealing furnace without overaging cannot be made completely non-aging, and the stretcher / strain, etc. during processing after coating baking can not be performed. However, if the C content is 0.0015% or less, in combination with the integrated production method of the present invention described below, no overaging treatment is performed in the production of the steel sheet for soft containers. It was found that a non-aging steel sheet excellent in batch annealing steel sheet can be obtained even if it is annealed in a continuous annealing furnace.

The steel component having a C content of 0.0015% or less is a completely new steel component which has not been put to practical use in the form of the integrated manufacturing method of the present invention in the steel of the conventional steel sheet for containers. In the conventional steel composition range in which the C content exceeds 0.0015%, it is necessary to add a large amount of carbide-forming elements such as titanium and niobium in order to produce a non-aged steel sheet excellent in batch annealing steel sheet quality. However, there have been problems such as an increase in alloy cost, an increase in annealing temperature due to an increase in recrystallization temperature, and a decrease in productivity due to a difficulty in thin rapid annealing resulting therefrom. However, C of 0.0015% or less of the present invention
According to the method of using the content, it is not necessary to add a large amount of expensive alloy elements such as titanium and niobium, and the above problems can be solved. Further, in the conventional steel composition range in which the C content exceeds 0.0015%, when hot rolling at a temperature higher than about 700 ° C. is carried out by hot rolling, carbides of the hot rolled steel strip agglomerate, resulting in flanging workability and There was a problem that corrosion resistance deteriorates. However, according to the method of the present invention using a C content of 0.0015% or less, there is no concern that the carbides of the hot-rolled steel strip will agglomerate, no matter how high the winding temperature is. Can be taken. Thus, the C content is 0.0015
The significance of the present invention set to be less than or equal to% is extremely great. Note that C
The steel component having a content of 0.0015% or less can be industrially melted by a vacuum degassing apparatus or the like. For the above reasons, the C content is limited to 0.0015% or less. Particularly, it is preferable that the C content be as small as 0.0010% or less.

If the C content is 0.0015% or less,
In combination with the integrated production method of the present invention described below, even when performing annealing in a continuous annealing furnace without overaging treatment in the production of steel sheet for soft containers, excellent non-aging steel sheets similar to batch annealed steel sheets can be obtained. The mechanism is unclear. However, if the C content is 0.0015% or less, the solid solution C amount after continuous annealing measured by the internal friction method is not detected. Therefore, when the absolute amount of C is as small as 0.0015% or less, the solid solution C dissolved in the heating and soaking process of continuous annealing precipitates in the grain boundaries in a short time in the cooling process. It is considered possible that non-aging was obtained.

If the amount of Mn is less than 0.05%, hot brittleness occurs, and a steel sheet for containers cannot be manufactured. Therefore, Mn must be contained in an amount of 0.05% or more. On the other hand, if the amount exceeds 0.40%, the steel is hardened and the tempering degree T-3
Since it is not possible to manufacture the following soft container steel sheet,
It was limited to 0.05 to 0.40%.

Although it is not necessary to add P intentionally, it is an unavoidable impurity element that significantly hardens the steel, and if it exceeds 0.06%, a steel sheet for a soft container of T-3 or less cannot be manufactured, so its upper limit is 0. It was limited to 0.06%.

Although it is not necessary to add S intentionally, S is an unavoidable impurity element that promotes hot brittleness, and 0.06%
If it exceeds 1.0, the steel sheet for containers cannot be manufactured due to hot brittleness, so the upper limit was limited to 0.06%.

The acid-soluble Al needs to be 0.01% or more in order to fix the solid solution N harmful to aging as aluminum nitride. On the other hand, if the amount exceeds 0.10%, Al ₂ O ₃
Since the amount of system inclusions increases, which causes flange cracks and the like during molding, and also increases the cost, the upper limit is set to 0.
Limited to 10%.

N need not be intentionally added, but it is a harmful unavoidable impurity element that causes aging at the same time as hardening the steel, and when it exceeds 0.0060%, the steel sheet for containers as a product has an aging effect. Since a steel sheet for a soft container having a temper of T-3 or less cannot be obtained due to the occurrence of a solid solution hardening, the upper limit is limited to 0.0060%.

The steel having the above-described chemical composition can achieve the object of the present invention in combination with the following manufacturing steps and conditions.
The manufacturing process and conditions of the present invention will be described below. The steel of the present invention is produced by using a normal melting furnace such as a converter or an electric furnace, or is additionally melted by a vacuum degassing treatment or the like, and is subjected to an ingot agglomeration method or a continuous casting method to form a hot steel piece (slab). To do. Prior to hot rolling, the hot billet is once cooled to 950 ° C. or lower in order to precipitate N which is harmful to aging as aluminum nitride. From this point of view, in the present invention, it is necessary to avoid containing a large amount of N, and it is necessary to add an appropriate amount of Al.

The steel bill thus cooled is then reheated for hot rolling. The reheating temperature imparts hot workability, prevents remelting of aluminum nitride precipitated in the steel slab manufacturing process, and inhibits aluminum nitride from inhibiting crystal grain growth in the hot rolling step or subsequent steps. Not limited to 1200 ° C. or lower in order to precipitate in a relatively large form. If the reheating temperature is lower than 1000 ° C., the hot workability is deteriorated, and it becomes difficult to secure the hot rolling finish temperature at 850 ° C. or higher.
Limited to 0 ° C.

If the finishing temperature of hot rolling is lower than 850 ° C., the object of the present invention cannot be achieved for the reasons described below. First, it becomes difficult to control the plate thickness of the hot-rolled steel strip, so that it becomes difficult to control the plate thickness in the cold rolling, the plate thickness accuracy of the product steel plate deteriorates, and often the plate rupture occurs during the cold rolling operation. Wake up. This deterioration of the plate thickness accuracy of the product steel plate fundamentally impairs the object of the present invention to supply the container steel plate with the excellent shape accuracy of the continuous annealing method. Plate rupture during cold rolling operation fundamentally undermines the object of the present invention to produce a container steel sheet with high productivity in continuous annealing. Further, when the finishing temperature is lower than 850 ° C., a texture is formed in the hot-rolled steel strip, and as a result, the occurrence of earrings during drawing and ironing of the product steel sheet becomes large, which deteriorates the yield at the can manufacturer. .. This fundamentally undermines the purpose of the present invention to improve the yield and quality of the canmaker by applying the continuous annealing method. For the above reasons, the hot rolling finishing temperature must be limited to 850 ° C or higher.

The time from when the hot-rolled steel strip leaves the final finishing stand to when cooling on the run-out table is started, the ultra-thin steel sheet for soft containers is manufactured in a continuous annealing furnace with high productivity. For this purpose, it was limited to 1.5 seconds or less. It has been found that when the time period exceeds 1.5 seconds, the recrystallization temperature of the steel of the present invention rises, although the reason is not clear. Therefore, if this time exceeds 1.5 seconds, high temperature continuous annealing must be performed. In high temperature continuous annealing, the deformation resistance of the steel strip is significantly reduced, so that problems such as heat buckling in the furnace are likely to occur in the furnace.
Such a stripping problem is promoted as the strip thickness of the steel strip is smaller and the strip stripping speed of the continuous annealing furnace is higher, so the strip thickness of the steel strip is increased in order to perform high temperature annealing. In addition, the passing speed must be reduced. As a result, if the time exceeds 1.5 seconds, there is a problem that the object of the present invention to manufacture the ultra-thin steel sheet for soft containers with high productivity in a continuous annealing furnace cannot be achieved. Therefore, the inventors of the present invention have industrially operated the time from when the hot-rolled steel strip leaves the final finishing stand until the cooling on the run-out table is started, the recrystallization temperature, and the continuous annealing furnace. As a result of a detailed investigation of the limits of possible sheet thickness and sheet passing speed, in order to continuously anneal ultra-thin steel sheets for soft containers with a sheet thickness of 0.30 mm or less at high speed (300 m / min or more), hot rolling It is necessary to control the time from when the steel strip exits the finishing stand to when cooling on the run-out table starts to 1.5 seconds or less.

When the coiling temperature of the hot-rolled steel strip is lower than 650 ° C., the solid solution N harmful to aging cannot be sufficiently precipitated as aluminum nitride, and the non-aging target of the present invention is not achieved. Since it is not possible to manufacture steel sheets for flexible containers, the lower limit is set at 65.
Limited to 0 ° C. On the other hand, when the winding temperature exceeds 750 ° C., the pickling property is significantly deteriorated, and the purpose of the present invention to manufacture the steel sheet for containers with high productivity is impaired. Therefore, the winding temperature is limited to 650 to 750 ° C.

The hot-rolled steel strip produced in this manner is pickled according to the usual steel sheet manufacturing process for containers,
After cold rolling, recrystallization annealing is performed in a continuous annealing furnace. As a method for annealing the cold-rolled steel strip, both batch annealing and continuous annealing which are usually performed can be adopted. However, batch annealing is less productive than continuous annealing, its quality is non-uniform, it consumes a lot of energy, requires a large number of operating personnel, and has a long manufacturing period. The object of the present invention for producing a highly excellent container steel sheet with high productivity is impaired. Therefore, the annealing method needs to be a continuous annealing method.

The continuous annealing method may or may not be overaged. However, continuous annealing with overaging treatment requires a long continuous annealing furnace with overaging treatment zone, which not only leads to increase in equipment cost, but also high-speed annealing of thin wide steel strip, which is required recently from the viewpoint of resource saving, is difficult. Therefore, the continuous annealing method is preferably a continuous annealing without overaging treatment.

The annealed steel strip is temper-rolled. If the elongation percentage of this temper rolling is less than 0.6%, it becomes difficult to adjust the shape and the surface roughness.
Limited to%. Further, if it exceeds 10%, work hardening becomes excessive, and a steel sheet for a soft container having a temper of T-3 or less cannot be obtained, so the upper limit was limited to 10%. Then, surface treatment such as tin plating, tin-free steel plating, ultra-thin tin plating, and nickel plating is performed to obtain a steel sheet product for containers.

[0029]

EXAMPLES Steel having the components shown in Table 1 was melted in a converter,
Steel pieces (slabs) produced by the continuous casting method are cooled to the lowest temperature as shown in Table 2 and then heated to the slab reheating temperature shown in the same table prior to hot rolling to finish temperature and hot rolling. The time from when the steel strip leaves the final finishing stand to when it starts cooling on the run-out table (cooling start time) and at the coiling temperature, hot rolling to a plate thickness of 3.0 mm and pickling Then, cold rolling was performed to a sheet thickness of 0.22 mm, recrystallization annealing was performed in a continuous annealing furnace at a soaking temperature of 650 ° C. and a sheet passing rate of 500 m / min, and temper rolling was performed at the temper rolling elongation rate shown in Table 2. A product was obtained by performing electrotin plating with a basis weight # 25.

Rockwell hardness (HR30-T) after reflow treatment of the product thus obtained, fluting workability results after aging at 210 ° C. × 30 minutes, stretcher resistance after aging at 210 ° C. × 30 minutes Table 3 shows the strain performance results and the earring results after the reflow treatment.

The Rockwell hardness is evaluated by JIS.
It carried out based on Z2245. For evaluation of fluting workability, cylindrical bending was carried out with a tester consisting of three rolls having a diameter of 40 mm, and the occurrence of waist bending was visually observed. Then, only those in which the waist was not observed at all were judged as "pass", and those in which even a slight waist was observed were judged as "fail".

The stretcher / strain resistance was evaluated by using a hydraulic bulge tester to constrain the test piece in a circular shape having a diameter of 190 mm and molding the inside of the circumference to a strain amount of 3% by hydraulic pressure. Overhang molding was performed up to the height, and the occurrence of stretcher strain patterns on the surface was observed. Then, only those with no observed stretcher strain were judged as “pass”, and those with even a slight stretcher strain were judged as “failed”.

The evaluation of the earring results was carried out by drawing the cup with a cup forming machine in a laboratory and measuring the earring rate. In the case of this test method, the earring rate is 3%
It is known that any customer will pass if it is below, so if the earring rate is 3% or less, "pass",
More than 3% was judged as "fail". In addition, when cracking occurred during drawing and cup molding could not be performed, it was described as "cracking".

Further, the aging condition of 210 ° C. × 30 minutes is stricter than any of the aging conditions of coating baking performed by various consumers, and a steel sheet subjected to the aging treatment of 210 ° C. × 30 minutes is a fluting or stretcher. -It is known that if the strain is not shown, it can be regarded as a complete non-aging.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

In Tables 1 to 3, product numbers 1 to 8 are steels of the present invention, and product numbers 9 to 16 are steels of the present invention. The underlined items in product numbers 9 to 16 differ from the constituent features of the present invention. As can be seen from Tables 1 to 3, the steels of the present invention are soft steel sheets having temper grades of T-1 to T-3, and do not generate fluting or stretcher strain after aging and are completely non-aged. Shows sex. It also has excellent earring properties.

On the other hand, among the steels not included in the present invention, the product numbers 9 and 10 are inferior in fluting resistance and stretcher / strain resistance, presumably because the steel components, particularly the C content, deviate from the scope of the present invention. Also in the product number 11, the contents of Mn, P and N deviate from the scope of the present invention, the hardness exceeds the tempering degree of T-3, and the stretcher / strain resistance is also poor. Product No. 12 is the aging property which is considered to be because the minimum achievable temperature of the slab before hot rolling is out of the range of the present invention,
That is, fluting and stretcher strain. The product number 13 shows the aging property which seems to be because the slab reheating temperature is out of the range of the present invention. The product number 14 shows a defective earring property which is considered to be because the hot rolling finishing temperature is out of the range of the present invention. Product number 15
Indicates that the hot rolling coiling temperature is out of the range of the present invention, and that the hot rolling steel strip finishes cooling the run-out table after leaving the finishing stand. Shows the cracks at the time of drawing due to the non-recrystallized material, which is considered to be outside the scope of the present invention. The product number 16 shows hardness which is considered to be because the temper rolling elongation is out of the range of the present invention.

[0040]

According to the present invention, the refining degree is T-3 or less, without adding expensive alloy elements such as titanium and niobium.
In addition, the plate thickness has the same non-aging property as that of the batch annealed steel plate.
It provides a method capable of industrially producing a thin soft container steel sheet of 30 mm or less at a high speed of 300 m / min or more even in a continuous annealing furnace without overaging treatment, and its industrial value is extremely high. large.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiko Yamashita 1-1 Tobahata-cho, Tobata-ku, Kitakyushu, Fukuoka Prefecture Inside Nippon Steel Co., Ltd. Yawata Works (72) Masayuki Matsuda Tobata-ku, Kitakyushu, Fukuoka No. 1 No. 1 Tobatacho Shin Nippon Steel Co., Ltd. Yawata Works (72) Inventor Takehide Senuma 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd.

Claims (1)

[Claims] 1. By weight%, C: 0.0015% or less, Mn: 0.05 to 0.40%, P: 0.06% or less, S: 0.06% or less, acid-soluble Al: 0. 01 to 0.10%, N: 0.0060% or less, a hot steel slab having the balance of iron and unavoidable impurities is once cooled to 950 ° C or less, and then reheated to a temperature of 1000 to 1200 ° C, and 850 After hot rolling at a finishing temperature of ℃ or more, 650 to 750 while cooling on the run-out table within 1.5 seconds after the hot-rolled steel strip exits the finishing stand of the hot rolling mill. Winding at a temperature of ℃, pickling, cold rolling, annealing in a continuous annealing furnace, then 0.6
A method for producing an ultra-thin steel sheet for soft non-aging containers by continuous annealing, which comprises temper rolling at an elongation of 10%.