WO2011021646A1 - Highly processable steel sheet for three-piece welded can and method for producing same - Google Patents

Abstract

Disclosed is a highly processable steel sheet for a three-piece welded can, which is suitable for practical use. The highly processable steel sheet for a three-piece welded can contains, in mass%, more than 0.0015% but 0.0030% or less of C, 0.10% or less of Si, 0.20-0.80% (inclusive) of Mn, 0.001-0.020% (inclusive) of P, 0.001-0.020% (inclusive) of S, more than 0.040% but 0.100% or less of Al, 0.030% or less of N, 0.0002-0.0050% (inclusive) of B, with the balance made up of Fe and unavoidable impurities. The highly processable steel sheet for a three-piece welded can has a tensile strength in the transverse direction to the rolling direction of 400 MPa or more, and an elongation at break in the transverse direction to the rolling direction of 15% or more. The steel sheet is able to be obtained by hot rolling a steel, which has the above-described composition, at a finish rolling temperature of not less than the Ar₃ transformation point but not more than 960˚C and a winding temperature of 560-750˚C (inclusive), then subjecting the resulting to a primary cold rolling at a reduction of 89-93% and an annealing at 600-790˚C, and then subjecting the resulting to a secondary cold rolling at a reduction of more than 6.0% but less than 10.0%.

Description

Steel plate for high workability 3-piece welded can and manufacturing method thereof

The present invention relates to a steel plate for cans having good workability even when the plate thickness is reduced, and a method for producing the same.

In recent years, in order to expand the demand for steel cans, measures have been taken to reduce can manufacturing costs. One of the measures to reduce the cost of can manufacturing is to reduce the cost of raw materials, and not only the two-piece cans that are drawn, but also the three-piece cans mainly made of cylindrical molding can reduce the thickness of the steel sheet used. It is being advanced.

For three-piece cans, where the can body is cylindrically formed by welding and the bottom and lid are joined to the can body by tightening, SR (Single Reduce) material manufactured by one cold rolling followed by annealing and temper rolling In a beverage can such as coffee, a steel plate having a thickness of about 0.175 mm is used.

Further, as a means for thinning the steel plate, there is a method using a DR (Double Reduce) material that is cold-rolled again after annealing, and it is easy to reduce the plate thickness as compared with the SR material. This DR material is mainly used for a drawn can as a steel plate for a can.

When using a DR material for a 3-piece can, the workability of the steel plate becomes a problem. In order to wind the lid and the bottom of the three-piece can body, the cylinder is molded and then flanged to widen the diameters at both ends. Cylindrical forming mainly uses a method in which a rectangular steel plate is rolled and energized and welded, but when a DR material is used, the steel plate may be cracked in the vicinity of the weld during flange processing. In particular, as a method for producing a three-piece beverage can, recently, a method of welding the can body along the rolling direction of the steel sheet has been mainstream. Therefore, elongation deformation in flange processing is mainly in the direction perpendicular to the rolling direction of the steel sheet, and workability in this direction is important.

Also, some canned beverages such as coffee go through a retort sterilization process after filling the contents. In this retort sterilization process, since the can is exposed to the pressure of water vapor exceeding 100 ° C., the strength of the can that can withstand the external pressure is required. In this case, it is the strength of the steel plate in the circumferential direction of the can body that affects the strength of the can body. When the can body is welded along the rolling direction of the steel plate, the strength of the steel plate in the direction perpendicular to the rolling direction is important.

In view of the above, Patent Document 1 discloses a method for improving the workability of the welded portion by adding B in an amount corresponding to the amount of C and the thickness of the ultra-low carbon steel.

Patent Document 2 discloses a method of manufacturing a steel sheet having excellent weldability equivalent to a tempering degree T3 by appropriately controlling the weight ratio of B and N in an ultra-low carbon steel.

Patent Document 3 discloses a method of manufacturing a steel sheet having high workability by controlling the form, type, and amount of nitride and sulfide in the B-added ultra-low carbon steel within an appropriate range. .

Japanese Patent No. 3379375 Japanese Patent Laid-Open No. 2001-247917 Japanese Patent Laid-Open No. 2003-231948

However, each of the above conventional techniques has the following problems.

Since the steel sheet described in Patent Document 1 has a high secondary rolling rate, the ductility in the direction perpendicular to the rolling direction is insufficient, and there is no problem when welding is performed along the direction perpendicular to the rolling direction of the steel sheet. When the can body is welded, there is a high possibility of cracking during flange processing, which is not suitable as a steel plate for a three-piece beverage can.

The steel sheet manufacturing method described in Patent Document 2 is insufficient in steel sheet strength to be applied to the thinning of a three-piece beverage can steel sheet because the steel sheet to be manufactured has a hardness of about tempering T3. In addition, secondary rolling with a specified rolling rate of 3.5 to 6% is too large to produce in a temper rolling facility with a rolling rate of usually 1 to 2%, and the load on the facility is excessive. Therefore, the rolling rate is too small to produce in a secondary rolling facility that uses a large amount of lubricant, and there is a high possibility that rolling defects such as chattering will occur.

Since the steel sheet produced by the manufacturing method described in Patent Document 3 contains a large amount of S, it has poor high-temperature ductility, and there is a risk of cracking when producing a steel slab by continuous casting.

The present invention has been made in view of such circumstances, and a steel plate for a highly workable three-piece welded can having a rolled perpendicular direction tensile strength of 400 Mpa or more suitable for practical use as a steel plate for a three-piece beverage can and excellent flange workability. And it aims at providing the manufacturing method.

The present inventors have conducted intensive research to solve the above problems. As a result, the following knowledge was obtained.

Since DR material is cold-rolled again after annealing, it becomes harder than SR material. Therefore, in order for a steel plate to have favorable workability, it is necessary to have sufficient elongation at break, that is, a soft material. In this respect, the carbon steel becomes softer as the C content is smaller. Therefore, in the present invention, an extremely low carbon steel is used.

Also, the DR material is strained by secondary cold rolling, and recrystallization occurs in the vicinity of the weld due to heat applied during welding. Since the recrystallized region is softer than the other portions, deformation concentrates during the flange processing and causes cracks. In order to prevent this, it is necessary to impart hardenability to the steel sheet. By adding an appropriate amount of B, the hardenability at the time of welding is increased, and softening in the vicinity of the welded portion can be prevented. However, when the secondary cold rolling rate is reduced, the strength of the welded portion becomes larger than that of the surrounding base material due to the quenching effect, so that deformation concentrates on the base material in the vicinity of the welded portion at the time of flange processing, resulting in cracks. For this reason, it is necessary to restrict the rolling reduction of secondary cold rolling to an appropriate range.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] By mass%, C: more than 0.0015% and 0.0030% or less, Si: 0.10% or less, Mn: 0.20% or more and 0.80% or less, P: 0.001% or more and 0.00. 020% or less, S: 0.001% or more and 0.020% or less, Al: more than 0.040% and 0.100% or less, N: 0.030% or less, B: 0.0002% or more and 0.0050% or less The balance is made of Fe and inevitable impurities, the tensile strength in the direction perpendicular to the rolling is 400 MPa or more, and the elongation at break in the direction perpendicular to the rolling is 15% or more. Steel plate for welding cans.
[2] By mass%, C: more than 0.0015% to 0.0030% or less, Si: 0.10% or less, Mn: 0.20% to 0.80%, P: 0.001% to 0.000. 020% or less, S: 0.001% or more and 0.020% or less, Al: more than 0.040% and 0.100% or less, N: 0.030% or less, B: 0.0002% or more and 0.0050% or less The balance is made of steel having a component composed of Fe and inevitable impurities, and the slab is made into a slab by continuous casting, and the slab is finished at the rolling temperature Ar ₃ transformation point to 960 ° C., and the winding temperature is 560 ° C. to 750 ° C. Hot-rolled, then primary cold-rolled at a rolling rate of 89% to 93%, annealed at 600 ° C to 790 ° C, and then rolled at a rolling rate of more than 6.0% and less than 10.0%. High workability 3 pin characterized by secondary cold rolling A method for producing steel plates for steel welding cans.
In addition, in this specification,% which shows the component of steel is mass% altogether.

According to the present invention, a steel sheet for a high workability three-piece weld can having a rolling perpendicular tensile strength of 400 Mpa or more and excellent flange workability can be obtained.

Specifically, the present invention provides a secondary cold rolling of a steel sheet for a three-piece welded can with excellent workability by adding B to an ultra-low carbon steel and setting the secondary cold rolling rate to an appropriate value. By the method, it can be reliably manufactured with a thin plate thickness.

As a result, by improving the workability of the original plate (steel plate), it is possible to make a can with a DR material having a thin plate thickness without causing cracks during the flange processing of the three-piece can, and a significant reduction in the thickness of the three-piece can is achieved. .

Hereinafter, the present invention will be described in detail.

The steel sheet for a highly workable three-piece welded can of the present invention is characterized in that the tensile strength in the direction perpendicular to the rolling is 400 MPa or more and the elongation at break in the direction perpendicular to the rolling is 15% or more. The steel sheet for a three-piece welded can with high workability of the present invention adds B to the ultra-low carbon steel and imparts hardenability while remaining soft, and sets the secondary cold rolling rate to an appropriate condition. By doing so, it is manufactured as an ultrathin steel plate by the secondary cold rolling method while ensuring the flange workability of the welded portion.

The component composition of the steel plate for high workability three-piece welded cans of the present invention will be described.

C: more than 0.0015% and 0.0030% or less In the present invention, in order to ensure the workability after secondary cold rolling, it is necessary to use a soft steel material. Generally, steel increases as the amount of C increases, so the upper limit of the C content is set to 0.0030%. If the amount of C exceeds 0.0030%, the workability of the steel sheet is impaired, and can manufacturing such as flange processing becomes difficult. On the other hand, if the C content is 0.0015% or less, the decarburization cost increases in the refining process, which is not preferable. Therefore, the lower limit of the C content is more than 0.0015%.

Si: 0.10% or less If the amount of Si exceeds 0.10%, problems such as deterioration of surface treatment property and deterioration of corrosion resistance are caused.

Mn: 0.20% or more and 0.80% or less Mn is an element necessary to prevent red heat embrittlement during hot rolling by S and to refine crystal grains and to secure a desirable material. . In order to exert these effects, it is necessary to add at least 0.20% or more. On the other hand, if Mn is added in a large amount, the corrosion resistance is deteriorated and the steel sheet is hardened to deteriorate the flange workability and the neck workability, so the upper limit is made 0.80%.

P: 0.001% or more and 0.020% or less P is a harmful element that hardens steel, deteriorates flange workability and neck workability, and at the same time deteriorates corrosion resistance. .020%. Moreover, dephosphorization cost becomes excessive in order to make P amount less than 0.001%. Therefore, the lower limit of the P content is 0.001%.

S: 0.001% or more and 0.020% or less S exists as an inclusion in steel, and is a harmful element that causes reduction in ductility and deterioration in corrosion resistance. Further, if the amount of S is excessive, high temperature ductility becomes poor, which leads to slab cracking in continuous casting. If the S amount exceeds 0.020%, these adverse effects become obvious, so the S amount is limited to 0.020% or less. On the other hand, the desulfurization cost is excessive to make S less than 0.001%, and even if the amount of S is further lowered from 0.001%, the above-mentioned adverse effects are hardly received. Therefore, the lower limit of the S amount is 0.001%.

Al: more than 0.040% and 0.100% or less Al is an element necessary as a deoxidizer during steelmaking. When the amount of Al is 0.040% or less, deoxidation becomes insufficient, inclusions increase, and flange workability deteriorates. On the other hand, when the Al content exceeds 0.100%, the occurrence frequency of surface defects due to alumina clusters and the like increases. Therefore, the Al amount is set to more than 0.040% and 0.100% or less.

N: 0.030% or less When N is added in a large amount, the hot ductility deteriorates and cracking of the slab occurs in continuous casting.
Therefore, the upper limit of the N amount is 0.030%.

B: 0.0002% or more and 0.0050% or less B is an essential element for preventing softening of the welded portion, and if it is less than 0.0002%, the performance is not sufficiently exhibited. Therefore, the lower limit of the B amount is 0.0002%. On the other hand, even if the amount of B exceeds 0.0050%, further performance improvement cannot be expected, but the cost is increased. Therefore, the upper limit of the B amount is set to 0.0050%. Preferably, it is 0.0011% or more and 0.0020% or less.

The balance is Fe and inevitable impurities.

Next, the manufacturing method of the steel plate for high workability three-piece welded cans of the present invention will be described.

The steel plate for high workability three-piece welded cans of the present invention is manufactured by applying hot rolling, primary cold rolling, annealing treatment and secondary cold rolling using a steel slab having the above composition produced by continuous casting. The The steel plate manufactured according to the present invention is assumed to be applied to thinning of a steel plate for a three-piece beverage can. Therefore, the product sheet thickness is required to be thinner than the conventionally used steel sheet, and it is necessary to roll to about 0.15 mm or less. Usually, it is difficult to achieve a sheet thickness of 0.15 mm or less by only one cold rolling. That is, in order to obtain a thin plate thickness by cold rolling, the load on the rolling mill is excessive. In order to reduce the sheet thickness after cold rolling, it is conceivable that rolling is performed thinner than usual in the hot rolling stage, but if the rolling rate of hot rolling is increased, the temperature of the steel sheet during rolling is decreased. The predetermined finish rolling temperature cannot be obtained. Furthermore, if the plate thickness before annealing is reduced, when continuous annealing is performed, the possibility of troubles such as breakage and deformation of the steel plate during annealing increases. For these reasons, in the present invention, the second cold rolling is performed after annealing.

Finish rolling temperature Ar ₃ transformation point or more and 960 ° C. or less When the final rolling temperature of hot rolling is less than Ar ₃ transformation point, the recrystallized grain size after annealing becomes non-uniform, and when it exceeds 960 ° C., the recrystallized grain after annealing The diameter becomes coarser than necessary. Therefore, the finish rolling temperature of the hot rolling is set to Ar ₃ transformation point or higher and 960 ° C. or lower. More preferably, it is 890 degreeC or more and 930 degrees C or less.

If the coiling temperature after hot rolling is less than 560 ° C, the recrystallized grain size after annealing becomes too fine. Moreover, when it exceeds 750 degreeC, the material of the whole steel plate will become non-uniform | heterogenous, and since the amount of scale production | generation becomes excessive, it is unpreferable. Therefore, the coiling temperature after hot rolling is set to 560 ° C. or higher and 750 ° C. or lower. More preferably, it is 600 degreeC or more and 720 degrees C or less.

Primary cold rolling The primary cold rolling rate affects the grain size after annealing when the rolling rate is 89% or more and 93% or less. If it is less than 89%, the recrystallized grain size becomes excessive, and if it exceeds 93%, it becomes excessively small. . Therefore, the primary cold rolling rate is 89% or more and 93% or less. More preferably, it is 90% or more and 92% or less.

The annealing temperature at 600 ° C. or higher and 790 ° C. or lower affects the recrystallization rate and the particle size. That is, when the temperature is lower than 600 ° C., the number of non-recrystallized grains becomes excessive and the workability is impaired. If it exceeds 790 ° C, the particle size becomes too large, and it becomes difficult to ensure the strength. Therefore, the annealing temperature is set to 600 ° C. or higher and 790 ° C. or lower. More preferably, it is 610 degreeC or more and 700 degrees C or less. Note that non-recrystallized grains may remain after annealing.

If the rolling rate is more than 6.0% and less than 10.0%, and the secondary cold rolling rate is 6.0% or less, the work hardening by the secondary cold rolling is insufficient and necessary. The strength of the steel sheet is not obtained. Further, the strength difference between the welded portion whose strength is increased by the quenching effect at the time of welding and the base material becomes large, and a crack occurs in the vicinity of the welded portion during the flange processing. On the other hand, if the secondary cold rolling rate is 10.0% or more, work hardening by secondary cold rolling becomes excessive, and sufficient elongation at break cannot be obtained. In addition, since the accumulated amount of strain due to secondary cold rolling is large, the ratio of recrystallized grains (recrystallization rate) in the vicinity of the welded portion increases, and the strength in the vicinity of the welded portion decreases, resulting in cracking during flange processing It becomes easy. From the above, the secondary cold rolling rate is more than 6.0% and less than 10.0%.

The subsequent steps such as plating are performed as usual, and finished as a steel plate for cans.

By the above, the steel plate for high workability 3 piece welding cans of this invention is obtained. And this workability is high, and the steel plate for 3 piece welding cans has a tensile strength in the direction perpendicular to the rolling of 400 MPa or more and a breaking elongation in the direction perpendicular to the rolling of 15% or more.
The strength in the direction perpendicular to the rolling direction is important in order to withstand the external pressure in the retort sterilization process when applied to a three-piece beverage can body that is welded along the rolling direction. The tensile strength in the direction perpendicular to the rolling direction is 400 MPa or more. Even if exposed to the environment, there will be no dents or buckling.
In addition, the elongation at break in the direction perpendicular to the rolling direction is important in order to prevent cracking during flange processing when applied to a three-piece beverage can body that is welded along the rolling direction. By doing so, it becomes possible to perform flange processing without causing any cracks.

Steel containing the composition shown in Table 1 and the balance being Fe and inevitable impurities was melted in an actual converter, and a steel slab was obtained by a continuous casting method. Subsequently, the obtained steel slab was reheated at 1250 ° C., and then subjected to hot rolling, primary cold rolling, continuous annealing, and secondary cold rolling under the conditions shown in Table 2 to 0.14 to 0.15 mm. The plate thickness was used. After hot rolling, pickling is performed. The steel plate produced as described above was continuously subjected to Sn plating on both surfaces to obtain a tinplate having a single-side Sn adhesion amount of 2.8 g / m ² .

A tensile test was performed on the plated steel sheet (blink) obtained as described above after a heat treatment equivalent to coating baking at 210 ° C. for 20 minutes. In the tensile test, tensile strength (breaking strength) and elongation at break in the direction perpendicular to rolling were measured in accordance with JIS Z2241 using a JIS No. 5 size tensile test piece.

In addition, a can body having an outer diameter of 52.8 mm was formed by seam welding using a steel plate that had been subjected to heat treatment equivalent to paint baking, and the end portion was necked in to an outer diameter of 50.4 mm and then flanged to an outer diameter of 55.4 mm. Processing was performed to evaluate the presence or absence of flange cracking. The case where cracking occurred at the flange processed part was evaluated as x, and the case where cracking did not occur was evaluated as ◯.

The can body was formed into a 190 g beverage can size and welded along the rolling direction of the steel sheet. Neck-in processing was performed by a die neck method, and flange processing was performed by a spin flange method.
A paneling test was conducted to evaluate the strength of the can body. A hollow can body was manufactured by performing the above-described processing and tightening of the lid and the bottom, and an external pressure was applied by air pressure in a sealed chamber, and a pressure at which the can body was crushed was measured. Crushing pressure was evaluated as ○ and the case where less than 1.7kg / cm ² ×, of 1.7 kg / cm ² or more. This standard is set as the strength that can withstand the pressure during general retort processing. In addition, 15 bead processes were given to the center part of the can body before the neck-in process. The bead spacing is 4 mm and the depth is 0.5 mm.

Table 3 shows the results obtained as described above.

From Table 3, No. which is an example of the present invention. Nos. 1 to 7 are excellent in strength and have achieved a tensile strength in the perpendicular direction of rolling of 400 MPa or more, which is necessary for thinning several percent of the can body of a three-piece can. The elongation at break in the direction perpendicular to the rolling is also 15% or more. Moreover, it is excellent in workability, and no cracks are generated in flange processing. The strength of the can after the can-making is sufficient.

On the other hand, no. Since No. 8 has too much C content, ductility is impaired by secondary cold rolling, and workability is inferior.
Moreover, No. of the comparative example. Since No. 9 does not contain B, the weld heat affected zone is extremely softened, and cracks are generated in the flange processing.
Comparative Example No. Nos. 10 and 11 have insufficient workability because the secondary cold rolling rate is too large. Comparative Example No. 12 and 13 are insufficient in strength because the secondary cold rolling rate is too small. Further, since the strength difference between the welded portion hardened by welding and the base material is large, cracks are generated in the flange processing.

Since the steel plate for a three-piece welded can of the present invention has high workability and excellent flange workability, it is suitably used for beverage cans such as coffee. Furthermore, it is possible to obtain a steel plate for a highly workable can with a thin plate thickness, and a significant reduction in the thickness of a three-piece can is achieved.

Claims (2)

1. By mass%, C: more than 0.0015% and 0.0030% or less, Si: 0.10% or less, Mn: 0.20% or more and 0.80% or less, P: 0.001% or more and 0.020% or less S: 0.001% or more and 0.020% or less, Al: 0.040% or more and 0.100% or less, N: 0.030% or less, B: 0.0002% or more and 0.0050% or less The balance consists of Fe and inevitable impurities, the tensile strength in the direction perpendicular to the rolling is 400 MPa or more, and the elongation at break in the direction perpendicular to the rolling is 15% or more. steel sheet.
2. By mass%, C: more than 0.0015% and 0.0030% or less, Si: 0.10% or less, Mn: 0.20% or more and 0.80% or less, P: 0.001% or more and 0.020% or less S: 0.001% or more and 0.020% or less, Al: 0.040% or more and 0.100% or less, N: 0.030% or less, B: 0.0002% or more and 0.0050% or less The balance is made of steel having a component consisting of Fe and inevitable impurities, and slab is formed by continuous casting.
   The slab is hot-rolled at a finish rolling temperature Ar ₃ transformation point or higher and 960 ° C. or lower, a coiling temperature 560 ° C. or higher and 750 ° C. or lower, and then primary cold-rolled at a rolling rate of 89% or higher and 93% or lower, and 600 ° C. or higher A method for producing a steel sheet for a high workability three-piece welded can, comprising annealing at 790 ° C. or lower and then performing secondary cold rolling at a rolling rate of more than 6.0% and less than 10.0%.