JP2013028842A - Steel plate for high strength high workability can and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel plate for a high-strength high-workability can and to provide a method for manufacturing the same.SOLUTION: The steel plate includes: 0.001% or more and 0.080% or less of C; 0.003% or more and 0.100% or less of Si; 0.10% or more and 0.80% or less of Mn; 0.001% or more and 0.100% or less of P; 0.001% or more and 0.020% or less of S; 0.005% or more and 0.100% or less of Al; 0.0050% or more and 0.0150% or less of N; 0.0002% or more and 0.0050% or less of B; and the balance of Fe and inevitable impurities. The cross-section surface in the rolling direction includes, in area ratio, 0.01-1.00% of crystal grains whose elongation rate is 5.0 or more. Such steel plate for cans can be obtained in the following. The slab reheating temperature of such steel plate is set at 1,200°C or higher, the steel plate is wound up at 650°C or lower after hot rolling, primary cold rolling is performed thereon, then continuous annealing is performed at a soaking temperature of 680-760°C for a soaking time of 10-20 seconds, and secondary cold rolling is performed thereon at a reduction ratio of 20% or lower.

Description

  The present invention relates to a steel plate for cans having high strength and high workability, and a method for producing the same.

  Among steel plates used for beverage cans and food cans, steel plates called DR (Double Reduce) materials may be used for lids, bottoms, 3-piece can bodies, drawn cans, and the like. DR material, which is cold-rolled again after annealing, is easier to reduce the thickness than SR (Single Reduce) material, which only performs temper rolling with a small rolling ratio. Can be reduced.

  In the DR method for producing a DR material, work hardening occurs by performing cold rolling after annealing, so that a thin and hard steel plate can be produced. However, on the other hand, the DR material manufactured by the DR method has poor ductility, so that the workability is inferior to that of the SR material.

  The body of food cans and beverage cans composed of three pieces is molded into a cylindrical shape, and then flanged at both ends in order to tighten the lid and bottom. Therefore, good elongation is required at the end of the can body.

  On the other hand, the steel plate as a can-making material requires strength according to the plate thickness, and in the case of DR material, tensile strength (about 520 MPa or more) is higher than that of SR material in order to ensure the economic effect of thinning. Needed.

  Conventionally used DR materials are difficult to achieve both the above-mentioned processability and strength, and SR materials have been mainly used for food cans and beverage cans. However, at present, in order to reduce the plate thickness from the viewpoint of cost reduction, it is desired to use DR material for the body of food cans and beverage cans, and the demand for expanding the application of DR material is increasing ing.

In response to this, Patent Document 1 discloses a DR material having excellent flange workability by setting the solid solution N amount in the low carbon steel to a certain amount or more and defining the total elongation value and the Rankford value. ing.
Patent Document 2 discloses a DR material excellent in flange workability by defining the amount of solute N and amount of solute C in low carbon steel.

JP 2007-177315 A JP 2002-294399 A

  However, all of the above conventional techniques have problems.

  In Patent Document 1, when X represents the total elongation value in the rolling direction and Y represents the average rankford value, X ≧ 10% and Y ≧ 0.9, or X <10% and Y ≧ −0.05X + 1.4. Although a DR steel sheet satisfying the above relationship is disclosed, depending on the welding conditions, HAZ softening still occurs and flange cracking occurs.

  In the manufacturing method described in Patent Document 2, since overaging treatment is essential in the continuous annealing step, the manufacturing cost becomes excessive.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a steel plate for a high-strength, high-workability can that is suitable as a material for a lid, a bottom, a three-piece can body, and the like, and a method for manufacturing the same.

The inventors of the present invention have intensively studied to solve the above problems. As a result, the following knowledge was obtained.
In order to achieve both workability and strength, it is necessary to secure the workability by adding an appropriate amount of N to limit the secondary cold rolling rate after annealing to an appropriate range. It is valid.
Further, if the slab reheating temperature before hot rolling is low, the AlN deposited after casting is not sufficiently remelted, and if the coiling temperature after hot rolling is high, the precipitated AlN becomes excessive. In any case, since the solute N responsible for the strength is insufficient, the slab reheating temperature and the winding temperature must be limited to an appropriate temperature range.
Furthermore, a good balance between strength and workability can be realized by limiting the annealing temperature and annealing time 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: 0.001% to 0.080%, Si: 0.003% to 0.100%, Mn: 0.10% to 0.80%, P: 0.001% to 0.100%, S: 0.001% to 0.020% Hereafter, Al: 0.005% or more and 0.100% or less, N: 0.0050% or more and 0.0150% or less, B: 0.0002% or more and 0.0050% or less, and the balance consists of Fe and inevitable impurities, and further, in the cross section in the rolling direction A steel plate for a high-strength, high-workability can, characterized by containing 0.01 to 1.00% in terms of area ratio of crystal grains having a grain elongation of 5.0 or more.
[2] By mass%, C: 0.001% to 0.080%, Si: 0.003% to 0.100%, Mn: 0.10% to 0.80%, P: 0.001% to 0.100%, S: 0.001% to 0.020% In the following, Al: 0.005% or more and 0.100% or less, N: 0.0050% or more and 0.0150% or less, B: 0.0002% or more and 0.0050% or less, and the balance is made of steel consisting of Fe and unavoidable impurities into slabs by continuous casting, After performing hot rolling with a slab reheating temperature of 1200 ° C or higher, winding at a temperature of less than 650 ° C, followed by primary cold rolling, followed by a soaking temperature of 680-760 ° C and a soaking time of 10-20 A method for producing a steel plate for a high-strength, high-workability can, characterized by performing continuous annealing in seconds and then performing secondary cold rolling at a rolling rate of 20% or less.
In addition, in this specification,% which shows the component of steel is mass% altogether.

According to the present invention, it is possible to obtain a high-strength and highly workable steel plate for cans having a tensile strength of 520 MPa or more and a breaking elongation of 7% or more.
As a result, by improving the workability of the original plate (steel plate), it is possible to make cans using DR material with a thin plate thickness, without causing cracks during flange processing of 3-piece cans. .

Hereinafter, the present invention will be described in detail.
The steel plate for cans of the present invention is a high-strength, high-workability steel plate for cans having a tensile strength of 520 MPa or more and a breaking elongation of 7% or more. Such a steel sheet uses steel containing N of 0.0050% or more and 0.0150% or less, and uses a slab reheating temperature before hot rolling, a winding temperature after hot rolling, an annealing temperature, an annealing time, and two It becomes possible to manufacture by setting the next cold rolling rate to an appropriate condition.

The component composition of the steel plate for cans of this invention is demonstrated.
C: 0.001% to 0.080%
When the amount of C exceeds 0.080%, workability deteriorates and cold rollability also decreases. In addition, subperitectic cracks are likely to occur during casting, which may increase costs such as slab care. For this reason, the C content is 0.080% or less. On the other hand, when the amount of C is less than 0.001%, crystal grains become prominent and the risk of rough skin defects occurring in the processed portion increases. Therefore, the C content is 0.001% or more and 0.080% or less.

Si: 0.003% to 0.100%
If the amount of Si exceeds 0.100%, problems such as deterioration of surface treatment properties and deterioration of corrosion resistance are caused, so the upper limit is made 0.100%. On the other hand, if it is less than 0.003%, the refining cost becomes excessive, so the lower limit is made 0.003%.

Mn: 0.10% to 0.80%
Mn has an effect of preventing red heat embrittlement during hot rolling due to S and refines crystal grains, and is an element necessary for securing a desirable material. In order to exert these effects, it is necessary to add at least 0.10%. On the other hand, if too much Mn is added, the corrosion resistance deteriorates and the steel sheet becomes excessively hard, so the upper limit is made 0.80%.

P: 0.001% to 0.100%
P is a harmful element that hardens steel and deteriorates workability and at the same time deteriorates corrosion resistance. Therefore, the upper limit is made 0.100%. On the other hand, the P removal cost is excessive to make P less than 0.001%. Therefore, the lower limit is made 0.001%.

S: 0.001% to 0.020%
S exists as an inclusion in steel, and is a harmful element that causes deterioration in workability and corrosion resistance. Therefore, the upper limit is made 0.020%. On the other hand, in order to make S less than 0.001%, the cost of removing S becomes excessive. Therefore, the lower limit is made 0.001%.

Al: 0.005% to 0.100%
Al is an element necessary as a deoxidizer during steelmaking. When the addition amount is small, deoxidation becomes insufficient, inclusions increase, and workability deteriorates. If the content is 0.005% or more, it can be considered that deoxidation is sufficiently performed. On the other hand, when the content exceeds 0.100%, the frequency of occurrence of surface defects due to alumina clusters and the like increases. Therefore, the Al content is 0.005% or more and 0.100% or less.

N: 0.0050% or more and 0.0150% or less In the steel plate for cans of the present invention, the secondary cold rolling rate is suppressed to ensure elongation, while increasing the N amount contributes to high strength. If the N content is less than 0.0050%, the tensile strength of 520 MPa necessary for obtaining a remarkable economic effect by thinning the steel sheet cannot be obtained. Therefore, the N content is 0.0050% or more. On the other hand, if the N content exceeds 0.0150%, it becomes excessively hard, and it becomes difficult to produce a thin steel plate by secondary cold rolling while ensuring workability. Therefore, the N content is 0.0150% or less.

B: 0.0002% to 0.0050%
B has the effect of suppressing grain growth in the heat-affected zone near the weld and preventing cracking during flange processing due to local strength reduction. In order to sufficiently obtain the effect of preventing such cracking, the amount of B needs to be 0.0002% or more. On the other hand, if it exceeds 0.0050%, no further effect can be expected, resulting in high costs. Therefore, the B content is 0.0002% or more and 0.0050% or less.

  The balance is Fe and inevitable impurities, but may contain component elements generally contained in known steel sheets for welding cans. For example, Cr: 0.10% or less, Cu: 0.20% or less, Ni: 0.15% or less, Mo: 0.05% or less, Ti: 0.3% or less, Nb: 0.3% or less, Zr: 0.3% or less, V: 0.3% or less, Component elements such as Ca: 0.01% or less can be contained depending on the purpose.

  Next, the crystal grains of the steel sheet for a high-strength and high-workability can according to the present invention will be described.

  In the cross section in the rolling direction, it is necessary that the crystal grains having a degree of elongation of 5.0 or more be included in an area ratio of 0.01 to 1.00%. Usually, when a DR material is produced using N steel as shown above, the degree of elongation of crystal grains in the cross section in the rolling direction is less than 3.0. However, by limiting the annealing temperature and annealing time to appropriate ranges, the degree of elongation of some crystal grains appears to increase. And although the mechanism is not clear, the workability is improved when crystal grains having an extension degree of 5.0 or more are present at an area ratio of 0.01% or more. If the area ratio exceeds 1.00%, the processability is adversely affected. From the above, the area ratio of crystal grains having a degree of extension of 5.0 or more is set to 0.01 to 1.00%.

The degree of elongation of the crystal grains in the cross section in the rolling direction can be measured by a microscopic test method for crystal grain size described in the document “JIS G 0551”. Further, according to the steel composition / manufacturing method of the present invention, the cementite and pearlite to be formed are very small compared to the ferrite grains, so the measurement of the crystal grain size and elongation is performed only on the ferrite crystal grains.
The area ratio of crystal grains can be measured by the point calculation method shown in the document “JIS G 0555 Annex 1”. This is intended for measuring the area ratio of non-metallic inclusions in steel materials, but can also be used for measuring the area ratio of crystal grains having a specific shape as described above. It is also possible to measure the area ratio using a micrograph and an arbitrary image analysis device.

Next, the manufacturing method of the steel plate for cans of this invention is demonstrated.
The steel sheet for high strength and high workability cans of the present invention uses a steel slab having the above composition produced by continuous casting, and the slab reheating temperature before hot rolling is 1200 ° C. or more, and after hot rolling Winding at a temperature below 650 ° C., followed by primary cold rolling, followed by continuous annealing at a soaking temperature of 680 to 760 ° C. and a soaking time of 10 to 20 seconds, and then at a rolling rate of 20% or less Manufactured by secondary cold rolling.

  Usually, it is difficult to obtain a thin plate thickness that can provide a remarkable economic effect by only one cold rolling. That is, in order to obtain a thin plate thickness by a single cold rolling, the load on the rolling mill is excessive, which is impossible depending on the equipment capacity. For example, when the final plate thickness is 0.15 mm, the primary cold rolling rate as large as 92.5% is required when the plate thickness after hot rolling is 2.0 mm. 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. A 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 to obtain an extremely thin steel plate.

Slab reheating temperature before hot rolling: 1200 ° C or more If the slab reheating temperature before hot rolling is less than 1200 ° C, the AlN deposited after casting will not be sufficiently remelted, and solid solution N will bear strength The amount is insufficient. Therefore, the slab reheating temperature before hot rolling is set to 1200 ° C. or higher. Preferably, it is 1200-1300 degreeC.

Winding temperature after hot rolling: less than 650 ° C. When the winding temperature after hot rolling is 650 ° C. or more, AlN is excessively precipitated, and the amount of solute N responsible for strength becomes insufficient. Therefore, the coiling temperature after hot rolling is less than 650 ° C. Preferably, it is 580-620 degreeC.

Primary cold rolling The primary cold rolling rate is not particularly limited, but in order to finally obtain an extremely thin steel plate, the rolling rate of the primary cold rolling needs to be large to some extent. That is, increasing the hot rolling rate is not preferable for the above-described reason, and the secondary cold rolling rate needs to be limited for the reason described later. Therefore, the primary cold rolling rate is preferably more than 85%. More preferably, it is 89 to 92%.

The annealing is performed by continuous annealing, the soaking temperature is 680 to 760 ° C., and the soaking time is 10 to 20 seconds. If the soaking temperature is less than 680 ° C, or the soaking time is less than 10 seconds, the area ratio of the crystal grains with the elongation in the rolling direction cross section exceeding 5.0 exceeds 1.00%, and the workability is insufficient. It becomes. In addition, if the soaking temperature exceeds 760 ° C or the soaking time exceeds 20 seconds, the area ratio of the crystal grains with a degree of elongation of 5.0 or more in the rolling direction cross section will be less than 0.01%, and the effect of improving workability Cannot be obtained.

Secondary cold rolling rate: 20% or less The secondary cold rolling rate is 20% or less. When the secondary cold rolling rate exceeds 20%, work hardening becomes excessive, and a breaking elongation of 7% or more cannot be obtained. Therefore, the secondary cold rolling rate is 20% or less. Preferably, it is 10% or more and 20% or less.
After the secondary cold rolling, steps such as plating are performed as usual, and finished as a steel plate for cans.

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. The obtained steel slab was reheated under the conditions shown in Table 2, and subjected to hot rolling and primary cold rolling under the conditions shown in Table 2. The finish rolling temperature of hot rolling is 890 ° C., and pickling is performed after hot rolling. Next, after the primary cold rolling, continuous annealing was performed under the conditions shown in Table 2, and then secondary cold rolling was performed under the conditions shown in Table 2.
The steel plate obtained as described above was continuously subjected to Sn plating on both sides to obtain a tinplate with a single-side Sn adhesion amount of 2.8 g / m ² .

  The plated steel sheet (blink) obtained as described above was subjected to a heat treatment equivalent to paint baking at 210 ° C. for 20 minutes, and then subjected to a tensile test. In the tensile test, tensile strength (breaking strength) and elongation at break in the direction perpendicular to rolling were measured using tensile test pieces of JIS No. 5 size.

  Also, a can body with an outer diameter of 52.8mm is formed by seam welding using a steel plate that has been heat-treated equivalent to paint baking, and the end is necked in to an outer diameter of 50.4mm and then flanged to an outer diameter of 55.4mm. The presence or absence of flange cracking was evaluated. The can body was formed into a 190 g beverage can size, and welding was performed 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. The case where a crack occurred in the flange processed part was evaluated as x, and the case where no crack occurred was evaluated as o.

Moreover, the sample of the plated steel plate was extract | collected and the area ratio of the crystal grain whose extension degree in a rolling direction cross section is 5.0 or more was measured. The elongation of the crystal grains in the cross section in the rolling direction is measured by the cutting method using the linear test line described in the literature “JIS G 0551” after polishing the vertical cross section of the steel sheet and revealing the grain boundary by nitral etching. did.
The results obtained are shown in Table 3.

  From Table 3, Nos. 1 to 5, which are examples of the present invention, are excellent in strength, and have achieved a tensile strength of 520 MPa or more required as an extremely thin steel plate for cans. It is also excellent in workability and has a break elongation of 7% or more necessary for processing of lids and 3-piece can bodies.

  On the other hand, No. 6 of the comparative example has too much C content, so the workability is impaired by secondary cold rolling and the elongation at break is insufficient. Since No. 7 of the comparative example does not contain B, the weld heat affected zone is extremely soft, and cracking occurs in the flange processing. No. 8 in the comparative example is too low for the slab reheating temperature, and No. 9 in the comparative example is too high in the coiling temperature. ing. No. 10 of the comparative example has insufficient tensile strength because the N content is too small. In Comparative Example No. 11, the soaking temperature of continuous annealing is too low, so that the area ratio of crystal grains having an extension degree of 5.0 or more is excessive, and the elongation at break is insufficient. Comparative Example No. 12 has a soaking temperature of continuous annealing that is too high, and Comparative Example No. 13 has a soaking time of continuous annealing that is too long. The area ratio is too small, and the elongation at break is insufficient. In Comparative Example No. 14, the secondary cold rolling rate is too large, so the work hardening is excessive and the elongation at break is insufficient.

  The steel plate for cans of the present invention has a tensile strength of 520 MPa or more, a breaking elongation of 7% or more, and can be obtained with a thin plate thickness. Therefore, it is optimal as a material for manufacturing can lids, can bottoms, 3-piece can bodies, etc. at low cost.

Claims (2)

In mass%, C: 0.001% to 0.080%, Si: 0.003% to 0.100%, Mn: 0.10% to 0.80%, P: 0.001% to 0.100%, S: 0.001% to 0.020%, Al : 0.005% or more and 0.100% or less, N: 0.0050% or more and 0.0150% or less, B: 0.0002% or more and 0.0050% or less, and the balance consists of Fe and inevitable impurities,
Furthermore, the steel sheet for high-strength and high-workability cans characterized by containing 0.01 to 1.00% in terms of area ratio of crystal grains having a degree of elongation of crystal grains of 5.0 or more in the cross section in the rolling direction.   In mass%, C: 0.001% to 0.080%, Si: 0.003% to 0.100%, Mn: 0.10% to 0.80%, P: 0.001% to 0.100%, S: 0.001% to 0.020%, Al : 0.005% or more and 0.100% or less, N: 0.0050% or more and 0.0150% or less, B: 0.0002% or more and 0.0050% or less, with the balance being steel made of Fe and inevitable impurities, made into a slab by continuous casting, and slab reheated After hot rolling at a temperature of 1200 ° C. or higher, winding at a temperature of less than 650 ° C., followed by primary cold rolling, and continuously with a soaking temperature of 680 to 760 ° C. and a soaking time of 10 to 20 seconds. A method for producing a steel plate for a high-strength, high-workability can, characterized by performing annealing and then performing secondary cold rolling at a rolling rate of 20% or less.