JP6274302B2 - Steel plate for 2-piece can and manufacturing method thereof - Google Patents

Description

  The present invention relates to a steel plate for cans suitable for can container materials used for food and beverage cans and a method for producing the same. In particular, the present invention relates to a two-piece can high-strength steel sheet having excellent formability and a method for producing the same, and the two-piece can high-strength steel sheet according to the present invention is a two-piece machined to the can body. It can be preferably applied to a deformed can.

  From the viewpoint of environmental load reduction and cost reduction in recent years, reduction of the amount of steel sheets used for food cans and beverage cans is required. For this reason, the thickness reduction of the steel plate used as a raw material is progressing irrespective of a 2 piece can and a 3 piece can.

  Recently, in order to compensate for the reduction in the strength of the can body due to the thinning of the steel sheet, the can body is often formed into a deformed can having a bead processing or a geometric shape. In the case of producing a two-piece can deformed can (sometimes referred to as a two-piece can), the can body is processed after forming with a relatively high degree of processing by drawing or ironing. For this reason, the steel plate used for manufacture of the two-piece can deformed can requires higher formability. On the other hand, the strength increase due to work hardening is small at the bottom of the can with a low degree of processing. For this reason, when the steel plate is thinned, the strength of the steel plate tends to be insufficient at the bottom of the can. In particular, in the case of a negative pressure can where the shape of the bottom of the can is flat, a strength higher than that of a conventional SR (Single Reduce) steel plate is required. For this reason, it is effective to use a DR (Double Reduce) steel plate that is easy to increase strength even if it is thinned at the bottom of the can.

  Since the DR steel sheet is hardened mainly by work hardening, the formability is generally low. If the moldability is low, it is not preferable for the can body as described above. Therefore, a technique for improving the formability of the DR steel sheet has been studied.

  For example, in Patent Document 1, in mass%, C: 0.001 to 0.10%, Mn: 0.05 to 0.50%, Al: 0.015 to 0.13%, Si: 0.05 %, P: 0.03% or less, S: 0.03% or less, with the balance being Fe and inevitable impurities, crystal grain size: 6-30 μm, centerline average roughness: 0.05- 0.6 μm, plate thickness: 0.15 to 0.30 mm electrolytic chromic acid-treated steel sheet coated on both sides with 10 to 50 μm thick thermoplastic resin, and dry squeezing with high temperature volatile lubricant applied to the surface A resin-coated steel sheet for a processing can is disclosed.

  In Patent Document 2, in mass%, C: 0.001 to 0.06%, Mn: 0.05 to 0.50%, Al: 0.015 to 0.13%, Si: 0.05% or less , P: 0.03% or less, S: 0.03% or less, with the balance being Fe and unavoidable impurities, after pickling, cold rolling, continuous annealing, at a rolling rate of 5-25% Rolled, centerline average roughness: 0.05 to 0.6 μm, plate thickness: 0.15 to 0.30 mm, then treated with electrolytic chromic acid, and then a thermoplastic resin having a thickness of 10 to 50 μm on both sides. A method for producing a resin-coated steel sheet for a dry-type squeezing and ironing can, which is coated and coated with a high-temperature volatile lubricant on the surface thereof, is disclosed.

  In Patent Document 3, in mass%, C: 0.02 to 0.07%, Si: 0.005 to 0.05%, Mn: 0.1 to 1.5%, P: 0.04% or less , S: 0.02% or less, Al: 0.005 to 0.1%, N: more than 0.003 to 0.007%, B: 0.001 to 0.01%, B / N: The relationship of 0.3 to 1.5 is satisfied, the balance is made of a steel composition of Fe and inevitable impurities, and the Rankford value (r value) of at least one of the rolling direction and the sheet width direction is 0.8 or less. A steel sheet for atypical cans is disclosed.

Japanese Patent No. 3140929 Japanese Patent No. 2937788 Japanese Patent No. 4630268

  However, the above prior art has the following problems.

  With the technique described in Patent Document 1, the moldability required when molding a straight can can be secured. However, the technique described in Patent Document 1 cannot ensure the formability required for forming a deformed can in which the can body is processed such as a processing bead.

  Even with the technique described in Patent Document 2, as with the technique described in Patent Document 1, the moldability required for forming a straight can can be secured. However, the technique described in Patent Document 2 similarly cannot secure the moldability required for forming a deformed can.

  The technique described in Patent Document 3 is for a three-piece can. The steel sheet described in Patent Document 3 has a large anisotropy because the r value of at least one of the rolling direction and the sheet width direction is 0.8 or less. This steel plate having large anisotropy does not have the formability required for forming a two-piece can including drawing.

  The present invention has been made in view of such circumstances, and solves the problems of the prior art described above, and in particular, provides a high-strength steel sheet for a two-piece can that can be preferably used for forming a two-piece deformed can and a method for manufacturing the same. The purpose is to do.

  The inventors of the present invention have intensively studied to solve the above problems. Specifically, in order to find a method for achieving both excellent strength required for the can bottom and excellent moldability required for the can body, as a result, component composition, tensile strength, elongation, The inventors have found that the above-mentioned problems can be solved by adjusting the yield elongation and the ferrite grain size to a specific range, and the present invention has been completed based on this finding.

  The present invention has been made based on the above findings, and the gist thereof is as follows.

  (1) By mass%, C: 0.020% or more and 0.080% or less, Si: 0.04% or less, Mn: 0.10% or more and 0.60% or less, P: 0.02% or less, S : 0.015% or less, Al: 0.010% or more and 0.100% or less, N: 0.0005% or more and 0.0030% or less, and the balance is made of Fe and inevitable impurities, and the tensile strength is A high-strength steel sheet for a two-piece can characterized by having 480 MPa or more, elongation of 7% or more, yield elongation of 3% or less, and ferrite grain size of less than 6 μm.

  (2) The high-strength steel sheet for a two-piece can according to (1), further containing, by mass%, B: 0.0001% or more and 0.0030% or less.

  (3) A method for producing a high-strength steel sheet for a two-piece can according to (1) or (2), wherein the slab is heated at a heating temperature of 1130 ° C. or higher, and the slab after the heating step, A hot rolling step of hot rolling under conditions of a hot rolling finishing temperature of 820 to 930 ° C, a winding step of winding the hot rolled sheet obtained in the hot rolling step at a winding temperature of 640 ° C or less, and A pickling process for pickling hot-rolled sheets after the winding process, a primary cold-rolling process for primary cold-rolling the hot-rolled sheets after pickling at a rolling rate of 85% or more, and the primary cold Conditions for a rolling rate of 6 to 20% for a continuous annealing process for continuously annealing a cold-rolled sheet obtained in the rolling process under conditions of an annealing temperature of 620 ° C. or more and 690 ° C. or less, and an annealing plate obtained in the continuous annealing process. High strength for two-piece cans characterized by having a secondary cold rolling step of secondary cold rolling at Method of manufacturing a steel plate.

  The high-strength steel sheet for a two-piece can of the present invention is adjusted to have a specific composition, has a tensile strength of 480 MPa or more, an elongation of 7% or more, a yield elongation of 3% or less, and a ferrite grain size of 6 It is adjusted to less than 0.0 μm. As a result, the high-strength steel sheet for a two-piece can of the present invention has excellent strength required for a can bottom and excellent formability required for a can body. Therefore, if the high-strength steel plate for a two-piece can according to the present invention is used, a two-piece modified can can be easily manufactured.

  As described above, according to the present invention, it is possible to reduce the thickness of a steel plate used for the production of food cans, beverage cans, etc., and it is possible to achieve resource saving and cost reduction. Play.

  Hereinafter, embodiments of the present invention will be described. In addition, this invention is not limited to the following embodiment.

<High-strength steel sheet for 2-piece cans>
The high-strength steel sheet for a two-piece can of the present invention is, in mass%, C: 0.020% or more and 0.080% or less, Si: 0.04% or less, Mn: 0.10% or more and 0.60% or less, P: 0.02% or less, S: 0.015% or less, Al: 0.010% or more and 0.100% or less, N: 0.0005% or more and 0.0030% or less, the balance being Fe and inevitable It has a component composition consisting of mechanical impurities.

  Moreover, about the physical property of the high strength steel plate for 2 piece cans of this invention, tensile strength is 480 Mpa or more, elongation is 7% or more, and yield elongation is 3% or less.

  In addition, the structure of the high-strength steel sheet for a two-piece can of the present invention is a structure having a ferrite particle size of less than 6 μm.

  Hereinafter, the high-strength steel sheet for a two-piece can of the present invention will be described in the order of component composition, physical properties, and structure.

  As described above, the high-strength steel sheet for a two-piece can according to the present invention is, in mass%, C: 0.020% or more and 0.080% or less, Si: 0.04% or less, Mn: 0.10% or more and 0.0. 60% or less, P: 0.02% or less, S: 0.015% or less, Al: 0.010% or more and 0.100% or less, N: 0.0005% or more and 0.0030% or less, and the balance Consists of Fe and inevitable impurities. The reason for adopting this component composition is as follows. In the following description, “%” representing the content of each component means “mass%”.

C: 0.020% or more and 0.080% or less C is an element important for strength improvement. By setting the C content to 0.020% or more, the tensile strength can be set to 480 MPa or more. Moreover, when C content exceeds 0.080%, elongation will fall to less than 7% and can manufacturing property will fall. Therefore, the upper limit of the C content needs to be 0.080%. Moreover, the larger the C content, the finer the ferrite grain size and the higher the strength. For this reason, the C content is preferably 0.030% or more. Further, from the viewpoint of securing canability, the C content is preferably 0.060% or less.

Si: 0.04% or less When a large amount of Si is contained, the surface treatment property deteriorates due to surface concentration, and the corrosion resistance decreases. For this reason, it is necessary to make Si content 0.04% or less. Preferably it is 0.03% or less.

Mn: 0.10% or more and 0.60% or less Mn has an effect of improving the hardness of the steel sheet by solid solution strengthening. Moreover, since Mn forms MnS, it is possible to prevent a decrease in hot ductility due to S contained in the steel. In order to acquire these effects, it is necessary to make Mn content 0.10% or more. In particular, the Mn content is preferably set to 0.30% or more so that tensile strength can be secured even if the rolling rate in DR rolling is reduced by solid solution strengthening with Mn. If the Mn content exceeds 0.60%, the elongation is remarkably lowered and the can-making ability is lowered. Therefore, the Mn content needs to be 0.60% or less.

P: 0.02% or less When a large amount of P is contained, formability is deteriorated due to excessive hardening or central segregation. Further, when P is contained in a large amount, the corrosion resistance is lowered. Therefore, the upper limit of the P content is 0.02%.

S: 0.015% or less S forms sulfides in steel and reduces hot ductility. Therefore, the upper limit of the S content is 0.015% or less.

Al: 0.010% or more and 0.100% or less Al forms N and AlN, thereby reducing solid solution N in the steel, lowering the yield elongation and suppressing stretcher strain. For this reason, it is necessary to make Al content 0.010% or more. From the viewpoint of reducing yield elongation and improving canability, the Al content is preferably 0.050% or more, and more preferably 0.060% or more. Further, when the Al content is excessive, a large amount of alumina is generated, and alumina remains in the steel sheet, resulting in a decrease in canability. Therefore, the Al content needs to be 0.100% or less. Preferably it is 0.080% or less.

N: 0.0005% or more and 0.0030% or less When N is present as a solid solution N, yield elongation increases, stretcher strain occurs, the surface appearance becomes poor, and the can-making ability decreases. For this reason, N content needs to be 0.0030% or less. Preferably it is 0.0025% or less. On the other hand, it is difficult to stably make the N content less than 0.0005%, and if the N content is made less than 0.0005%, the manufacturing cost also increases. For this reason, the lower limit of the N content is 0.0005%.

  The high-strength steel sheet for a two-piece can of the present invention preferably contains B as an optional component in the range of 0.0030% or less in addition to the above essential components.

B: 0.0001 to 0.0030%
B forms N and BN, reduces the solute N, and lowers the yield elongation. For this reason, it is preferable to contain B, and in order to obtain the effect of addition of B, the B content is preferably 0.0001% or more, and more preferably 0.0003% or more. Moreover, even if it contains B excessively, not only said effect will be saturated, but elongation will fall or anisotropy will deteriorate and can-making property will fall. Therefore, the upper limit of the B content is preferably 0.0030%.

  The balance other than the above essential components and optional components is Fe and inevitable impurities. Inevitable impurities include Cr: 0.08% or less, Cu: 0.02% or less, Ni: 0.02% or less, O: 0.006% or less.

  Next, the physical properties of the high-strength steel sheet for a two-piece can of the present invention will be described. As described above, the high-strength steel sheet for a two-piece can of the present invention has a tensile strength of 480 MPa or more, an elongation of 7% or more, and a yield elongation of 3% or less. The technical significance of each physical property is as follows, but in the present invention, the combination of these physical properties, the above component composition, and the structure described later, the strength required for the can bottom, and the can body are required. One of the important technical significances is that both excellent moldability and compatibility can be achieved.

Tensile strength: 480 MPa or more In order to ensure the strength of the bottom of the can, the tensile strength of the steel plate needs to be 480 MPa or more. Preferably it is 490 MPa or more. In addition, the value obtained by measuring with the method as described in an Example is employ | adopted for the tensile strength of a steel plate. In the present invention, the tensile strength is usually 580 MPa or less.

Elongation: 7% or more In addition to drawing and ironing processing, it is necessary to increase the elongation to 7% or more in order to ensure the processability of can bodies such as beads. Preferably it is 9% or more. By containing the steel components in a predetermined range and making the ferrite grain size finer under the manufacturing conditions described later, the elongation can be increased to 7% or more while being high strength of 480 MPa or more. It becomes possible to ensure canability. In addition, the value obtained by measuring with the method as described in an Example is employ | adopted for the elongation of a steel plate. In the present invention, the elongation is usually 25% or less.

Yield elongation: 3% or less Yield elongation needs to be 3% or less in order to prevent stretcher strain during canning. Preferably it is 2% or less. In addition, the value obtained by measuring with the method as described in an Example is employ | adopted for the yield elongation of a steel plate.

  Next, the structure of the high-strength steel plate for a two-piece can of the present invention will be described. The ferrite grain size in the structure of the high-strength steel sheet for a two-piece can of the present invention is less than 6 μm.

Ferrite particle size: less than 6 μm In addition to adjusting the component composition of the steel sheet as described above, the balance between increasing strength and elongation is improved by reducing the ferrite particle size. For this reason, it is necessary to make a ferrite particle size less than 6.0 micrometers. Further, by reducing the ferrite grain size to less than 6.0 μm and reducing the yield elongation to 3% or less, there is an effect of improving the adhesion between the resin coated on the steel sheet and the steel sheet surface. From this point of view, the ferrite grain size is preferably 5.5 μm or less. In addition, as described in the Examples, the particle size means an average crystal particle size.

  In the present invention, the content of the ferrite phase in the structure is preferably 95 vol% or more for the reason of improvement in elongation. More preferably, it is 98 vol% or more. Examples of phases other than the ferrite phase include cementite, pearlite, martensite, and bainite.

<Method for producing high-strength steel plate for 2-piece can>
As an example of a method for producing a high-strength steel sheet for a two-piece can of the present invention, a heating step, a hot rolling step, a winding step, a pickling step, a primary cold rolling step, a continuous annealing step, The manufacturing method which has a secondary cold rolling process is mentioned. Hereinafter, each step will be described.

Heating step The heating step is a step of heating the slab to a heating temperature of 1130 ° C or higher. When the heating temperature before hot rolling is too low, a part of AlN becomes undissolved. This undissolved becomes a cause of generation of coarse AlN that lowers the canability. Therefore, the heating temperature in the heating process is set to 1130 ° C. or higher. Preferably it is 1150 degreeC or more. The upper limit of the heating temperature is not particularly defined, but if the heating temperature is too high, excessive scale is generated, resulting in defects on the product surface. Therefore, the upper limit of the heating temperature is preferably 1260 ° C.

  In addition, since the component composition of the slab becomes the component composition of the high-strength steel plate for a two-piece can, the component composition of the slab needs to be adjusted so as to satisfy the component composition of the two-piece high-strength steel plate of the present invention. There is.

Hot rolling step The hot rolling step is a step of hot rolling the slab after the heating step under conditions of a hot rolling finishing temperature of 820 to 930 ° C. When the hot rolling finish rolling temperature is higher than 930 ° C., the ferrite grain size in the hot rolled sheet becomes coarse, the ferrite grain size in the annealed sheet becomes coarse, the tensile strength decreases, and the tensile strength and elongation. The balance will also worsen. For this reason, the upper limit of the hot rolling finishing temperature is set to 930 ° C. On the other hand, when the hot rolling finishing temperature is less than 820 ° C., the anisotropy of the tensile properties increases, and the can-making property is lowered. Therefore, the lower limit of the hot rolling finishing temperature is 820 ° C. A preferred lower limit is 860 ° C.

Winding process The winding process is a process in which the hot-rolled sheet obtained in the hot rolling process is wound at a winding temperature of 640 ° C or lower. When the coiling temperature exceeds 640 ° C., the ferrite grain size in the hot rolled sheet becomes coarse, the ferrite grain size in the annealed sheet becomes coarse, the tensile strength decreases, and the balance between tensile strength and elongation is poor. Become. For this reason, the upper limit of coiling temperature shall be 640 degreeC. Although the lower limit of the coiling temperature is not particularly defined, it is preferable to set the coiling temperature to 570 ° C. or higher from the viewpoint of generating AlN during winding, reducing the amount of dissolved N, and reducing yield elongation.

Pickling process The pickling process is a process of pickling the hot-rolled sheet after the winding process. The pickling conditions are not particularly limited as long as the surface scale can be removed. Pickling can be performed by a conventional method.

Primary cold rolling process The primary cold rolling process is a process in which the hot-rolled sheet after the pickling is subjected to primary cold rolling under conditions of a rolling rate of 85% or more. The rolling ratio of primary cold rolling needs to be 85% or more in order to refine the ferrite grain size after annealing and improve the balance between tensile strength and formability. If the rolling ratio in the primary cold rolling becomes too large, the anisotropy of tensile properties becomes large, and the can-making ability may be lowered. For this reason, it is preferable that the rolling rate of primary cold rolling shall be 90% or less.

Continuous annealing step The continuous annealing step is a step of continuously annealing the cold-rolled sheet obtained in the primary cold rolling step under conditions of an annealing temperature of 620 ° C or higher and 690 ° C or lower. In order to ensure formability, it is necessary to sufficiently recrystallize during annealing, so the annealing temperature needs to be 620 ° C. or higher. Further, if the annealing temperature is too high, the ferrite grain size becomes coarse, so the annealing temperature needs to be 690 ° C. or less. Although the annealing method is not limited, the continuous annealing method is preferable from the viewpoint of material uniformity.

Secondary cold rolling step The secondary cold rolling step is a step of secondary cold rolling the annealed sheet obtained in the continuous annealing step under the condition of a rolling rate of 6 to 20%. The annealed plate is strengthened and thinned by secondary cold rolling. In order to sufficiently increase the strength, the rolling rate needs to be 6% or more. Moreover, yield elongation reduces by secondary cold rolling. Moreover, if the rolling rate in the secondary cold rolling is too high, the formability deteriorates. Therefore, the rolling rate needs to be 20% or less. In particular, when formability is required, the rolling rate is preferably 15% or less.

  By the above, the high strength steel plate for 2 piece cans of this invention is obtained. As the surface treatment of the steel sheet, Sn plating, Ni plating, Cr plating or the like may be applied, and further an organic film such as chemical conversion treatment or lamination may be applied.

  A steel slab was obtained by melting steel containing components of steel symbols A to K shown in Table 1, with the balance being Fe and inevitable impurities. The obtained steel slab was heated under the conditions shown in Table 2 and then hot-rolled, wound, removed the scale by pickling, then primary cold-rolled, and each annealing temperature was adjusted in a continuous annealing furnace. The steel sheet was annealed for 15 s and subjected to DR rolling (secondary cold rolling) at the secondary rolling rate shown in Table 2 to obtain steel plates (steel plate symbols No. 1 to 18) having a thickness of 0.17 to 0.19 mm. The steel plate was subjected to chromium plating (tin-free) treatment as a surface treatment, and then a laminated steel plate coated with an organic film was produced.

Tensile Strength, Elongation, Yield Elongation After removing the organic coating with concentrated sulfuric acid from the laminated steel sheet, a JIS No. 5 tensile test piece was taken from the rolling direction, and in accordance with JIS Z 2241, tensile strength, elongation (total elongation), Yield elongation was evaluated.

Ferrite grain size After embedding in the cross section in the rolling direction, polishing, and corroding with nital to reveal grain boundaries, the average grain size was measured by a cutting method in accordance with JIS G 0551 to evaluate the ferrite grain size.

Evaluation of can manufacturing In order to evaluate the can manufacturing performance, after punching the above laminated steel sheet into a circular shape, deep drawing, ironing, etc. were performed to make a cylindrical shape. Bead processing was performed in the can circumferential direction at a total of three places of 15 mm in the vertical direction, and a can body similar to a two-piece can applied in a beverage can was formed. "◎" if there is no destructuring and almost no visible stretcher strain when making cans, "○" if there is no destructuring but a slight strain stretcher is recognized Was marked “x”.

  The results are shown in Table 3. In each of the examples of the present invention, the tensile strength is 480 MPa or more, the elongation is 7% or more, the yield elongation is 3% or less, and the ferrite particle size is less than 6.0 μm, and has excellent moldability and strength. On the other hand, in the comparative example, any one or more of the above characteristics are inferior. For example, steel plate symbols No. 9, 11, 13, and 17 have a can evaluation of “◯”, but the tensile strength of the steel plate is low, and it is not sufficient for the bottom of the can.

Claims (2)

In mass%, C: 0.038% to 0.080%, Si: 0.04% or less, Mn: 0.30 % to 0.60%, P: 0.02% or less, S: 0.00. 015% or less, Al: 0.010% or more and 0.080 % or less, N: 0.0005% or more and 0.0030% or less, with the balance being Fe and inevitable impurities,
The tensile strength is 480 MPa or more,
Elongation is 7% or more,
Yield elongation is 3% or less,
A steel plate for a two-piece can having a ferrite grain size of less than 6 μm. It is a manufacturing method of the steel plate for 2 piece cans of Claim 1,
A heating step of heating the slab at a heating temperature of 1130 ° C. or higher;
A hot rolling step in which the slab after the heating step is hot rolled under conditions of a hot rolling finishing temperature of 820 to 930 ° C;
A winding step of winding the hot-rolled sheet obtained in the hot rolling step at a winding temperature of 640 ° C. or less;
Pickling process of pickling hot-rolled sheet after the winding process;
A primary cold rolling step of primary cold rolling the hot-rolled sheet after pickling under a condition of a rolling rate of 85% or more;
A continuous annealing step of continuously annealing the cold-rolled sheet obtained in the primary cold rolling step under conditions of an annealing temperature of 620 ° C. or more and 690 ° C. or less;
A method for producing a steel plate for a two-piece can, comprising: a secondary cold rolling step of subjecting the annealed plate obtained in the continuous annealing step to secondary cold rolling under a condition of a rolling rate of 6 to 20%.