CN102482748A - Steel plate for three-piece welded tank with high workability and manufacturing method thereof - Google Patents

Abstract

A high-workability three-piece welded can steel sheet suitable for practical use, comprising, in mass%, C: greater than 0.0015% and below 0.0030%, 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: greater than 0.040% and less than 0.100%, N: 0.030% or less, B: 0.0002% to 0.0050%, with the balance being Fe and unavoidable impurities, and having a tensile strength of 400MPa or more in the direction perpendicular to rolling and an elongation at break of 15% or more in the direction perpendicular to rolling. The steel plate is obtained by the following method: at a finishing temperature of Ar₃The steel having the above composition is hot-rolled under conditions of a transformation point of not less than 960 ℃ and a coiling temperature of not less than 560 ℃ and not more than 750 ℃, then subjected to a primary cold rolling with a rolling reduction of 89 to 93% and an annealing treatment at 600 ℃ to 790 ℃, and then subjected to a secondary cold rolling with a rolling reduction of more than 6.0% and less than 10.0%.

Description

Steel plate for three-piece welded tank with high workability and manufacturing method thereof

technical field

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

Background technique

In recent years, in order to expand the demand for steel cans, strategies to reduce the cost of canning have been adopted. As one of the strategies to reduce the cost of can making, the cost reduction of raw materials can be cited. Not to mention the two-piece cans subjected to deep drawing, even the three-piece cans with cylindrical forming as the main body have been advancing the thinner steel plates used. walled.

For three-piece cans in which the body is cylindrically formed by welding, and the bottom and lid are joined to the body by seaming, SR (one-time Cold-rolled, Single Reduce) material, for beverage cans such as coffee, use a steel plate with a thickness of about 0.175mm.

In addition, as a method of thinning the steel plate, there is a method of using DR (Double Reduce) material that is cold-rolled again after annealing, and it is easier to reduce the plate thickness than SR material. The above-mentioned DR material is mainly used as a steel plate for cans for deep-drawn cans and the like.

When the DR material is used for a three-piece can, the workability of the steel sheet becomes a problem. For the three-piece can body, in order to curl the lid and the bottom, flanging is performed to increase the diameters of both ends after cylindrical molding. Cylindrical forming mainly uses a method of rolling rectangular steel plates into a cylinder and performing electric welding. However, when DR material is used, cracks may occur in the steel plate near the welded portion during flanging. In particular, recently, as a manufacturing method of three-piece beverage cans, the mainstream is a method of welding can bodies along the rolling direction of steel plates. Therefore, elongation deformation mainly occurs in the direction perpendicular to the rolling of the steel sheet in flanging, and workability in this direction becomes important.

In addition, some canned beverages such as coffee are subjected to a retort sterilization process after filling the contents. In this retort sterilization process, the can is exposed to the pressure of water vapor exceeding 100° C., and therefore, the strength of the can body capable of withstanding the above-mentioned 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 becomes important.

Based on the above background, Patent Document 1 discloses a method of improving the workability of welded parts by adding an amount of B to ultra-low carbon steel corresponding to the amount of C and the plate thickness.

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

Patent Document 3 discloses a method of manufacturing a steel sheet with high workability by controlling the form, type, and amount of nitrides and sulfides in B-added ultra-low carbon steel within appropriate ranges.

prior art literature

patent documents

Patent Document 1: Japanese Patent No. 3379375

Patent Document 2: Japanese Patent Laid-Open No. 2001-247917

Patent Document 3: Japanese Patent Laid-Open No. 2003-231948

Contents of the invention

The problem to be solved by the invention

However, each of the above-mentioned prior arts has the following problems.

For the steel sheet described in Patent Document 1, the secondary rolling rate is large, so the ductility in the direction perpendicular to rolling is insufficient, and there is no problem in the case of welding along the direction perpendicular to rolling of the steel sheet, but in the case of welding along the rolling direction of the steel sheet, there is no problem. In the case of welding the can body in the opposite direction, there is a high possibility of cracks during the flanging process, so it is not suitable as a steel plate for three-piece beverage cans.

The steel sheet manufacturing method described in Patent Document 2 has a steel sheet with a hardness of about tempering degree T3, and therefore, the steel sheet has insufficient strength when applied to thinning the steel sheet for three-sheet beverage cans. In addition, for the secondary rolling with a prescribed rolling rate of 3.5 to 6%, when the rolling rate is usually 1 to 2% for surface skin rolling equipment for manufacturing, the rolling rate is too large, so that the equipment The load becomes too large, and when manufacturing is performed by a secondary rolling facility that uses a large amount of lubricant, the rolling ratio is too small, and there is a high possibility of occurrence of rolling defects such as chattering.

The steel sheet produced by the production method described in Patent Document 3 contains a large amount of S, and therefore lacks high-temperature ductility, and may cause cracks when producing a steel slab by continuous casting.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a highly workable three-piece welded can having a tensile strength in the direction perpendicular to rolling of 400 MPa or more and excellent flanging workability, which is suitable for practical application to steel plates for three-piece beverage cans Steel plate and method for its manufacture.

method used to solve the problem

The inventors of the present invention conducted intensive studies in order to solve the above problems. As a result, the following insights were obtained.

Since the DR material is subjected to cold rolling again after annealing, it becomes harder than the SR material. Therefore, in order for the steel sheet to have good workability, it needs to have a sufficient elongation at break, that is, it needs to be a soft material. From the above point of view, carbon steel becomes softer as the amount of C is smaller, so in the present invention, ultra-low carbon steel is used.

In addition, in the DR material, strain due to secondary cold rolling is introduced, and recrystallization occurs in a region near the weld due to heat supplied during welding. The recrystallized region is softer than other parts, and therefore, during the flanging process, deformation is concentrated and cracks are generated. In order to prevent the above phenomenon, it is necessary to impart hardenability to the steel sheet. By adding an appropriate amount of B, the hardenability at the time of welding can be improved, and softening near the weld can be prevented. However, when the secondary cold rolling ratio is reduced, the strength of the welded portion becomes greater than that of the surrounding base material due to the through hardening effect, and therefore, during flanging, deformation concentrates in the base material near the welded portion to generate cracks. Therefore, it is necessary to limit the rolling ratio of the secondary cold rolling within an appropriate range.

This invention was completed based on the above knowledge, and the summary is as follows.

[1] A steel plate for three-piece welded cans with high workability, characterized by containing C: more than 0.0015% and not more than 0.0030%, Si: not more than 0.10%, and Mn: not less than 0.20% and 0.80% in mass % Below, P: 0.001% to 0.020%, S: 0.001% to 0.020%, Al: more than 0.040% to 0.100%, N: 0.030%, B: 0.0002% to 0.0050%, and the rest The content is composed of Fe and unavoidable impurities, the tensile strength in the direction perpendicular to rolling is 400 MPa or more, and the elongation at break in the direction perpendicular to rolling is 15% or more.

[2] A method of manufacturing a steel plate for three-piece welded cans with high workability, characterized in that the steel is made into a slab by continuous casting, and the finishing temperature is not less than the Ar ₃ transformation point and not more than 960°C, and the coiling temperature is The steel slab is hot-rolled at a temperature of 560°C to 750°C, followed by primary cold rolling at a rolling reduction of 89% to 93% at a temperature of 600°C to 790°C annealing, followed by secondary cold rolling at a rolling reduction of more than 6.0% and less than 10.0%, wherein the steel has the following composition, in mass %, containing C: more than 0.0015% and less than 0.0030%, 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: more than 0.040% and 0.100% or less, N: 0.030% Below, B: not less than 0.0002% and not more than 0.0050%, and the balance is composed of Fe and unavoidable impurities.

In addition, in this specification, all the % which shows a steel component is mass %.

Invention effect

According to the present invention, a highly workable steel sheet for three-piece welded cans having a tensile strength in the rolling direction perpendicular to 400 MPa and excellent flanging workability can be obtained.

Specifically, in the present invention, by adding B to ultra-low carbon steel and setting the secondary cold rolling ratio to an appropriate value, it is possible to reliably produce a steel plate with excellent workability with a thin plate thickness by the secondary cold rolling method. Three pieces of steel plate for welded tanks.

As a result, by improving the workability of the original plate (steel plate), no cracks will occur during the flanging process of the three-piece can, and it is possible to make cans using DR material with a thin plate thickness, thereby achieving a large thinner three-piece can. walled.

Detailed ways

The present invention will be described in detail below.

The high workability steel sheet for three-piece welded cans of the present invention is characterized in that the tensile strength in the direction perpendicular to rolling is 400 MPa or more, and the elongation at break in the direction perpendicular to rolling is 15% or more. Therefore, in the steel sheet for three-piece welded cans with high workability of the present invention, hardenability is imparted in a soft state by adding B to ultra-low carbon steel, and the secondary cold rolling ratio is set to Under proper conditions, it is possible to manufacture an ultra-thin steel sheet by the secondary cold rolling method while ensuring the flanging workability of the welded portion.

The component composition of the highly workable steel sheet for three-piece welded cans of the present invention will be described.

C: more than 0.0015% and less than 0.0030%

In the present invention, in order to ensure workability after secondary cold rolling, it is necessary to set the raw material to soft steel. In general, as the amount of C increases, the steel becomes harder, so the upper limit of the C content is made 0.0030%. When the amount of C exceeds 0.0030%, the workability of the steel sheet is impaired, and can making such as flanging becomes difficult. On the other hand, it is not preferable to make the amount of C less than 0.0015%, since the cost of decarburization in the refining process will increase, so the lower limit of the amount of C is set to be greater than 0.0015%.

Si: 0.10% or less

If the amount of Si exceeds 0.10%, problems such as reduction of surface treatment property and deterioration of corrosion resistance will be caused, so it is made 0.10% or less.

Mn: 0.20% to 0.80%

Mn has the function of preventing red hot embrittlement in hot rolling caused by S and making crystal grains finer, and is an essential element for securing a preferable material. In order to exhibit these effects, it is necessary to add at least 0.20% or more. On the other hand, excessive addition of a large amount of Mn deteriorates the corrosion resistance and hardens the steel sheet, thereby deteriorating flanging workability and diameter reducing 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 to deteriorate flanging workability and diameter reducing workability, and also deteriorates corrosion resistance, so the upper limit is made 0.020%. In addition, if the amount of P is lower than 0.001%, the cost of dephosphorization becomes excessive. Therefore, the lower limit of the amount of P is made 0.001%.

S: 0.001% to 0.020%

S is a harmful element that exists in the form of inclusions in steel and causes a decrease in ductility and deterioration of corrosion resistance. In addition, when the amount of S is too large, the high-temperature ductility is poor, and therefore, cracks in the slab during continuous casting are caused. When the amount of S is more than 0.020%, these adverse effects become apparent, so the amount of S is limited to 0.020% or less. On the other hand, if S is lower than 0.001%, the cost of desulfurization will be too high, and further reducing the amount of S to less than 0.001% will hardly cause the above-mentioned adverse effects. Therefore, the lower limit of the amount of S is made 0.001%.

Al: more than 0.040% and less than 0.100%

Al is an essential element as a deoxidizing material in steelmaking. When the amount of Al is 0.040% or less, deoxidation becomes insufficient, inclusions increase, and flanging workability deteriorates. On the other hand, when the amount of Al exceeds 0.100%, the occurrence frequency of surface defects due to alumina clusters and the like increases. Therefore, the amount of Al is made more than 0.040% and not more than 0.100%.

N: 0.030% or less

When a large amount of N is added, the hot ductility deteriorates and cracks are generated in the slab during continuous casting. Therefore, the upper limit of the amount of N is made 0.030%.

B: 0.0002% or more and 0.0050% or less

B is an element necessary for preventing softening of welded parts, and if it is less than 0.0002%, its performance cannot be fully exhibited. Therefore, the lower limit of the amount of B is made 0.0002%. On the other hand, even if the amount of B exceeds 0.0050%, further improvement in performance cannot be expected, and rather leads to an increase in cost. Therefore, the upper limit of the amount of B is made 0.0050%. Preferably it is 0.0011% or more and 0.0020% or less.

The balance is set to Fe and unavoidable impurities.

Next, a method of manufacturing the highly workable steel sheet for three-piece welded cans of the present invention will be described.

The highly workable steel sheet for three-piece welded cans of the present invention can be produced by performing hot rolling, primary cold rolling, annealing treatment, and secondary cold rolling using a steel slab having the above composition produced by continuous casting. A case is assumed in which the steel sheet manufactured according to the present invention is applied to thinning of the steel sheet for a three-piece beverage can. Therefore, the thickness of the product sheet is required to be thinner than that of conventionally used steel sheets, and it is necessary to roll to about 0.15 mm or less. In general, it is difficult to obtain 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 becomes excessive. In addition, in order to reduce the plate thickness after cold rolling, it is also considered to roll to a thinner plate thickness than usual in the hot rolling stage, but when the rolling ratio of hot rolling is increased, the temperature drop of the steel plate during rolling becomes larger, Thus, the predetermined finish rolling temperature cannot be obtained. Furthermore, when the thickness of the sheet before annealing is reduced, when continuous annealing is performed, problems such as breakage and deformation of the steel sheet during annealing are more likely to occur. For the above reasons, in the present invention, the second cold rolling is performed after annealing.

The finish rolling temperature is above the Ar ₃ transformation point and below 960°C

When the finishing temperature of hot rolling is lower than the Ar ₃ transformation point, the recrystallized grain size after annealing becomes uneven, and when it exceeds 960° C., the recrystallized grain size after annealing becomes coarser than necessary. Therefore, the finishing temperature of hot rolling is set to be not less than the Ar ₃ transformation point and not more than 960°C. More preferably, it is 890°C or more and 930°C or less.

The coiling temperature is not less than 560°C and not more than 750°C

When the coiling temperature after hot rolling is lower than 560° C., the recrystallized grain size after annealing becomes too small. Moreover, when it exceeds 750 degreeC, since the material of the whole steel plate will become non-uniform, and the amount of scale formation will become too large, it is unpreferable. Therefore, the coiling temperature after hot rolling is 560°C or higher and 750°C or lower. More preferably, it is 600°C or more and 720°C or less.

Primary cold rolling at a rolling reduction rate of 89% to 93%

The primary cold rolling ratio affects the grain size after annealing, and when it is less than 89%, the recrystallized grain size becomes too large, and when it exceeds 93%, it becomes too small. Therefore, the primary cold rolling ratio is set to 89% or more and 93% or less. More preferably, it is 90% or more and 92% or less.

Annealing at a temperature above 600°C and below 790°C

The annealing temperature affects the recrystallization rate and particle size. That is, when the temperature is lower than 600° C., there are too many non-recrystallized crystal grains, which impairs workability. When the temperature exceeds 790° C., the particle size becomes too large, making it difficult to secure strength. Therefore, the annealing temperature is set to be 600°C or higher and 790°C or lower. More preferably, it is 610°C or more and 700°C or less. It should be noted that non-recrystallized crystal grains may remain after annealing.

Secondary cold rolling with a rolling ratio greater than 6.0% and less than 10.0%

When the secondary cold rolling ratio is 6.0% or less, the work hardening by secondary cold rolling is insufficient, and required steel sheet strength cannot be obtained. In addition, due to the through-hardening effect during welding, the strength difference between the welded portion with increased strength and the base material becomes large, and cracks are generated near the welded portion during flanging. On the other hand, when the secondary cold rolling ratio is 10.0% or more, work hardening due to secondary cold rolling becomes too large, and sufficient elongation at break cannot be obtained. In addition, since the accumulated amount of strain caused by the secondary cold rolling is large, the ratio of recrystallized grains (recrystallization rate) in the vicinity of the welded portion increases, and the strength of the vicinity of the welded portion decreases. prone to cracks. Based on the above, the secondary cold rolling ratio is set to be greater than 6.0% and less than 10.0%.

Subsequent processes such as plating are carried out in accordance with conventional methods, and finished into steel sheets for cans.

As described above, the highly workable steel sheet for three-piece welded cans of the present invention can be obtained. In addition, the steel sheet for three-piece welded cans having high workability has a tensile strength in a direction perpendicular to rolling of 400 MPa or more, and an elongation at break in a direction perpendicular to rolling of 15% or more.

In the case of applying to a three-piece beverage can body welded along the rolling direction, in order to withstand the external pressure in the retort sterilization process, the strength at right angles to rolling is important, and by making the tensile strength at right angles to rolling It is more than 400MPa, and even if it is exposed to the distillation environment, it will not produce pits or buckling at all.

In addition, in the case of applying to a three-piece beverage can body welded along the rolling direction, the elongation at break in the direction perpendicular to rolling is important in order not to cause cracks during flanging. The elongation at break is more than 15%, and flanging can be performed without cracks at all.

Example

Steel containing the composition shown in Table 1, with the balance consisting of Fe and unavoidable impurities was melted in an actual converter, and a billet was obtained by continuous casting. Next, the obtained steel slab was reheated at 1250° C., and hot rolling, primary cold rolling, continuous annealing, and secondary cold rolling were performed under the conditions shown in Table 2 to produce a plate of 0.14 to 0.15 mm. thick. Pickling is carried out after hot rolling. Sn plating was continuously performed on both surfaces of the steel sheet manufactured as above to obtain a tin-plated steel sheet with a Sn deposition amount of 2.8 g/m on ^one side.

The above-obtained plated steel sheet (tin-plated steel sheet) was subjected to a heat treatment corresponding to coating firing at 210° C. for 20 minutes, and then a tensile test was performed. In the tensile test, tensile strength (breaking strength) and elongation at break in a direction perpendicular to rolling were measured in accordance with JIS Z2241 using a tensile test piece of JIS No. 5 size.

In addition, using a steel plate subjected to a heat treatment equivalent to painting and sintering, a can body with an outer diameter of 52.8 mm was formed by seam welding, and the end was reduced in diameter to an outer diameter of 50.4 mm, and then flanged to an outer diameter of 50.4 mm. 55.4mm, to evaluate whether there is flanging cracks. The case where cracks occurred in the burring portion was evaluated as x, and the case where no cracks occurred was evaluated as ◯.

The can body is formed to the size of a 190g beverage can, and welded along the rolling direction of the steel plate. The diameter reduction process is carried out by the mold diameter reduction method, and the flanging process is carried out by the spinning flanging method.

Carry out evaluation test to evaluate the tank strength. The above-mentioned processing and crimping of the lid and the bottom are carried out to produce a hollow can body, and an external pressure from air pressure is applied in the closed cavity to measure the pressure when the can body is crushed. The case where the crush pressure was less than 1.7 kg/cm ² was evaluated as x, and the case where it was 1.7 kg/cm ² or more was evaluated as ○. This standard is set with the strength that can withstand the pressure at the time of ordinary distillation treatment. It should be noted that 15 reinforcing ribs were processed on the central part of the can body before the diameter reduction processing. The spacing of reinforcing ribs is 4mm and the depth is 0.5mm.

Table 3 shows the results obtained as above.

According to Table 3, Invention Examples Nos. 1 to 7 are excellent in strength, and achieve tensile strength in the rolling direction perpendicular to 400 MPa required for several percent thinning of the body of a three-piece can. The elongation at break in the direction perpendicular to rolling also reached 15% or more. In addition, workability is also excellent, and cracks do not occur even during flanging. The strength of the can body after canning is also sufficient.

On the other hand, in Comparative Example No. 8, the C content was too large, and therefore, the ductility was impaired due to secondary cold rolling, and the workability was deteriorated.

In addition, since Comparative Example No. 9 does not contain B, the weld heat-affected zone was extremely softened, and cracks were generated during the flanging process.

In Comparative Example Nos. 10 and 11, the secondary cold rolling ratio was too large, so the workability was insufficient. In Comparative Example Nos. 12 and 13, the secondary cold rolling ratio was too small, so the strength was insufficient. In addition, the strength difference between the welded portion hardened by welding and the base material is large, and therefore, cracks are generated during the flanging process.

Industrial availability

The steel sheet for three-piece welded cans of the present invention has high formability and excellent flanging workability, and therefore is preferably used for beverage cans such as coffee, for example. Furthermore, it is possible to obtain a steel sheet for cans with high workability at a thin thickness, thereby realizing a substantial reduction in wall thickness of a three-piece can.

Claims (2)

1. three of high working properties weld steel plate for tanks; It is characterized in that; In quality %; Contain C: greater than 0.0015% and below 0.0030%, below the Si:0.10%, more than the Mn:0.20% and below 0.80%, more than the P:0.001% and below 0.020%, more than the S:0.001% and below 0.020%, Al: greater than 0.040% and below 0.100%, below the N:0.030%, more than the B:0.0002% and below 0.0050%; Surplus is made up of Fe and unavoidable impurities, and the tensile strength of rolling right angle orientation is more than the 400MPa and the elongation at break of rolling right angle orientation is more than 15%.

2. the method for manufacture of three welding of high working property steel plate for tanks is characterized in that, steel is processed steel billet through continuous casting, is Ar in finishing temperature ₃Transformation temperature above and below 960 ℃, coiling temperature is more than 560 ℃ and under the condition below 750 ℃ said steel billet to be carried out hot rolling; Then; With more than 89% and 93% below rolling rate carry out once cold rolling; Implementing anneal more than 600 ℃ and under the temperature below 790 ℃; Then, with greater than 6.0% and implement secondary cold-rolling, wherein less than 10.0% rolling rate; Said steel has following composition; In quality %, contain C: greater than 0.0015% and below 0.0030%, below the Si:0.10%, more than the Mn:0.20% and below 0.80%, more than the P:0.001% and below 0.020%, more than the S:0.001% and below 0.020%, Al: greater than 0.040% and below 0.100%, below the N:0.030%, more than the B:0.0002% and below 0.0050%, surplus is made up of Fe and unavoidable impurities.