JP2007197742A - Cold rolled steel sheet for welded can, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for providing, with high productivity, a steel sheet for cans in which the formability of welded resealable cans can be remarkably improved and which has expanding workability capable of applying practical strength to can bodies after forming. <P>SOLUTION: In the steel sheet, the percentage of precipitated N is ≥85%, and the difference between hardness at a depth of 25 μm from the surface of the steel sheet in thickness direction and hardness in the central part of the steel sheet in thickness direction, after heating and holding at 170°C for 7 min, is ≥15 points by micro Vickers hardness. The steel sheet has a composition containing, by mass, 0.015 to 0.08% C, 0.10 to 0.60% Mn, ≤0.02% P, ≤0.02% S, 0.02 to 0.10% acid-soluble Al and ≤0.006% N. The sum of solid-solution N and solid-solution C, contained in the steel sheet, is 10 to 20 ppm and also a relation of [(solid-solution C)≥(solid-solution N)×2] is satisfied. Temper rolling is performed at a draft of 1.5 to 3.0% and a tension of 50 to 200 MPa using rolls of ≤470 mm roll diameter. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is suitable for deformed welded cans among steel plates for containers such as tinplate and tin-free steel, and has a tempering degree of T-3 or less and an equivalent St-St resistance (stoke resistance) equivalent to box annealing. The present invention relates to a steel plate for a soft container by a continuous annealing method having (retcher strain) properties and a method for producing the same.

  In recent years, deformed cans called reseal cans that have been made easy to open by using large-diameter caps on steel cans and have a reseal function have become widespread. This re-sealed can is generally embodied as a draw-molded type with no joints in the can body, but recently there has been an increasing trend toward differentiation due to the beauty of the appearance, and the weld-molded type with seams. New field development has begun. Welding has a high degree of freedom in can printing and can body forming, and in particular, since the can body can be expanded, the design of the can shape is far superior to the draw forming type.

  Steel sheets used in weld-type reseal cans have (a) high expandability and shape freezing properties in order to stably obtain a predetermined shape, and (b) stretcher strain ( (St-St) material that has no wrinkles, and (c) has sufficient yield strength that does not impair dent resistance when the material is thinned to reduce the mass of the can. Is desired. In order to satisfy such requirements, it is soft at the time of processing, and can easily improve the yield strength in the heat treatment after can body molding, and further has characteristics such as excellent aging properties. Necessary.

  Already cold rolled steel sheets for expanding by the box annealing method that have both the characteristics (a) and (b) are commercially available, but there is an essential problem that they are soft and weak in dent resistance. ) Is not improving. On the other hand, the cold-rolled steel sheet by the continuous annealing method has problems with respect to (a) and (b), but has a very high yield strength, and has desirable characteristics with regard to the reduction of the can body mass of (c).

  As an example of solving the problems (a) and (b) with a cold-rolled steel sheet by a continuous annealing method, a method for manufacturing a steel sheet for soft surface treatment in Patent Document 1 is disclosed. This is to reduce the solid solution N in the steel sheet after hot rolling (hot rolling) to 10 ppm or less using low carbon aluminum killed steel as a raw material, and to disperse and precipitate C as string-like or spherical cementite to maintain the form of AlN. The crystal grains are coarsened, the continuous annealing after cold rolling is performed at 650 to 710 ° C., and the temper rolling (temper rolling) is a dry roll having a rolling reduction of 1.5 to 5% with a small diameter roll having a roll diameter of 470 mm or less. By performing temper rolling, a steel sheet excellent in soft characteristics and fluting resistance advantageous for shape freezing property can be obtained. Here, fluting is a strain aging phenomenon similar to St-St that appears in the bending process of steel sheets, but since bending is not as severe as the expansion process, this technique is not sufficient as a steel sheet for expanding processes. is there.

Further, Patent Document 2 discloses a technique in which St-St resistance is improved by a continuous annealing method. The continuous annealing temperature is increased to over 710 ° C. to 780 ° C., and the temper rolling is further reduced to 3-7% by a wet temper rolling method using a small diameter roll having a roll diameter of 470 mm or less. Further, the strain aging due to the solid solution N is effectively suppressed, and a soft cold-rolled steel sheet having excellent St-St resistance can be manufactured. However, since this wet temper rolling method is a rolling method corresponding to ordinary cold rolling, a cold-rolled structure is formed on the steel sheet, and “yield strength is soft during processing and yields in heat treatment after forming the can body. However, there is a problem in that the property of “easily increases” is weakened and the shape freezing property and the expand moldability are not always sufficient.
JP 61-23719 JP-A-4-107218

  Therefore, the present invention has been devised in view of the above-described problems, and the object of the present invention is to freeze the shape remaining in a continuously annealed steel plate made of the conventional low carbon aluminum killed steel as described above. Improved properties and expand moldability without losing St-St resistance and dent resistance, "soft during processing, and yield strength easily increases during heat treatment after can molding" It is to establish a cold-rolled steel sheet for a welding can that can be utilized and a manufacturing method thereof.

  In order to solve the above-described problems, the present invention includes the following (1) to (4) as its constituent elements.

(1) Precipitation N ratio (NasAlN × 100 / total N) is 85% or more, and after heat retention at 170 ° C. for 7 minutes, the hardness in the thickness direction of 25 μm from the steel sheet surface and the thickness direction center of the steel sheet A cold-rolled steel sheet for welding cans, wherein the difference from the hardness is 15 points or more in terms of micro Vickers hardness.

(2) Mass% as a steel component, C: 0.015 to 0.08%, Mn: 0.10 to 0.60%, P: 0.02% or less, S: 0.02% or less, acid acceptable Molten Al: 0.02 to 0.10%, N: 0.006% or less, the balance is made of Fe and inevitable impurities, and the total of solid solution N and solid solution C contained in the steel sheet is 10 to 20 ppm. The cold-rolled steel sheet for welded cans according to (1), which has a relationship of solid solution C ≧ solid solution N × 2.

(3) Further, as a steel component in mass%, Nb: 0.001 to 0.003%, Ti: 0.001 to 0.003%, B: 0.0001 to 0.001%, Cu: 0.05% Hereinafter, it contains one or more elements selected from Ni: 0.05% or less, Cr: 0.05% or less, Mo: 0.05% or less, and V: 0.003% or less. (2) The cold-rolled steel sheet for welding cans.

(4) After the continuous cast slab of the component (2) or (3) is cooled to 700 ° C. or less, it is inserted into a hot rolling furnace and reheated to 950 to 1100 ° C., and then the finishing temperature is set at Ar 3 to 950. C., hot rolling at 650 to 720.degree. C., pickling, cold rolling, holding at a soaking temperature of 650 to 720.degree. C. for 10 to 60 seconds, cooling to 500.degree. C. or lower, and 300 to 500.degree. For a welding can characterized by performing continuous annealing for 60 seconds or more and then performing temper rolling with a roll having a roll diameter of 470 mm or less at a rolling reduction of 1.5 to 3.0% and a tension of 50 to 200 MPa. A method for producing a cold-rolled steel sheet.

  According to the present invention, the formability of a welded can-type reseal container is remarkably improved, and a steel plate for welded cans with expanded workability that enables practical strength to be imparted to the molded can body has high production. It can be provided with sex.

  While taking advantage of the characteristics of the continuously annealed steel sheet having excellent dent resistance shown in (c) above, the present inventors have (a) expand formability and shape freezing property, and (b) St-St (stretcher strain) resistance. Various studies were conducted on how to improve the required characteristics. First, the experimental results that led to the development of the present invention will be described. Hereinafter, mass% (mass%) in the composition is simply described as%.

  The inventor first made a cold-rolled steel sheet having a fine-grained structure by continuous annealing, and (c) improved dent resistance, and further box-annealed (b) caused a decrease in St-St resistance. The aim was to achieve both (a) expand formability and shape freezeability by reducing the amount of solid solution C and solid solution N to be extremely small and the accompanying improvement in elongation. Steel No. described in Tables 1 to 3 shown below. 1 and 2 are the experimental results.

  First, a steel plate was produced from the slab comprising the components shown in Table 1 under the production conditions shown in Table 2. Incidentally, this steel No. In the experiment about 1 and 2, continuous annealing and box annealing (holding time: 12 hours) are used together. The steel sheet after annealing was artificially aged by heating and holding at 170 ° C. for 7 minutes. After 10 mm overhanging by a hydraulic bulge tester, visual St-St observation and shape from variation (± 0.5 mm) with respect to the overhanging height of 10 mm Evaluation of freezing and the presence or absence of dent resistance by the yield strength of a tensile test using a JIS No. 5 specimen were confirmed. The results were organized into the material survey results in Table 3.

  Steel No. above. The following new findings were obtained through experiments on 1 and 2.

  1) Yield point elongation and YP-El value of steel plate subjected to artificial aging 1 is 0%, steel no. 2 is 1.2%, and the solid solution C and the solid solution N amount of the steel sheet are suppressed to be extremely low by the combined use of continuous annealing and box annealing, and the St-St resistance is excellent.

  2) On the other hand, even if the steel plate is refined by a combination of box annealing and continuous annealing, the shape freezing property is good because it is within ± 0.5mm with respect to the overhang height of 10mm, but after aging in the rolling direction. The yield strength is 284 to 287 MPa, which is less than 320 MPa as the yield strength necessary for dent resistance.

  3) However, extremely fine steel No. No. 1 and steel No. 1 which is a general crystal grain. No significant difference was found in the yield strength after aging of No. 2 because the strain aging hardening due to solid solution C and solid solution N was found in Steel No. It was inferred to be acting strongly on 2.

  Based on this knowledge of 3), in order to improve the dent resistance of the reseal can, it can be said that it is desirable to use an aging steel plate in which solute C and solute N remain in the steel. However, from the conventional knowledge, in order to use solute C and solute N, there is an upper limit of the amount of addition, and it is obvious that the temper rolling method is preferably dry.

  Next, the inventors proceeded with investigations on an optimal combination method of a limited amount of solute C and solute N remaining in the steel plate and a strain amount to be added to the steel plate by dry temper rolling. As a result, the inventors have come to know a preferable temper rolling method that improves St-St resistance without forming a cold-rolled structure on the steel sheet. That is, since the cold-rolled structure is formed by the tension during temper rolling, the rolling rate should be imparted to the steel sheet mainly by rolling with a rolling roll, and in addition, the rolling force is effectively distorted. It is desirable to use a small-diameter roll that can be converted into a steel sheet. On the other hand, it is preferable to limit the use of tension only to the correction of the shape of a steel sheet to suppress the formation of a cold-rolled structure. Steel Nos. Listed in Tables 1-3. 3-6 are the experimental results manufactured on the temper rolling conditions of Claim 4 of this invention. On the other hand, Steel No. 7 and 8 are comparative examples that deviate from the temper rolling conditions described in claim 4 of the present invention.

  Steel No. 3 to 6 are made of low carbon aluminum killed steel, the reheating temperature of hot rolling is about 1100 ° C., and the scraping temperature after hot rolling is about 670 ° C., so that the amount of solute N is 0.0003 to 0.00. Reduced to 0014%, pickled, cold-rolled, recrystallized at a continuous annealing temperature of 690 ° C, held at 400 ° C for 60 seconds or more and over-aged, then reduced to 2% with a small diameter roll of around 450mm A dry temper rolling with a degree of tension of 137 to 196 MPa was applied to a plate thickness of 0.19 mm. The amount of solute C in the obtained steel sheet was suppressed to 0.0006 to 0.0014% as measured by the internal friction method, and the tempering degree was T-3 and satisfied the material required for the reseal can.

  On the other hand, Steel No. 7 and 8 are steel Nos. After reducing the amount of dissolved N to 0.0007 to 0.0008% under the same hot rolling conditions as 3 to 6, pickling, cold rolling, continuous annealing, and overaging treatment were also performed under substantially the same conditions. A dry temper rolling with a rolling ratio of about 2% and a tension of 245 to 294 MPa was performed with a large diameter roll of 520 to 530 mm, and the plate thickness was set to 0.19 mm. The amount of solute C in the obtained steel sheet was 0.0009 to 0.0010% as measured by the internal friction method, and the tempering degree was T-3, which satisfied the material required for the reseal can.

  Steel No. manufactured as described above. 3-6 and steel no. For the steel sheets 7 and 8, first, artificial aging treatment was performed at 170 ° C. for 7 minutes to cause strain age hardening in the steel sheet, and then to confirm St-St generation and shape freezing property and dent resistance related to the expanding process. A 10 mm overhang using a hydraulic bulge tester and a tensile test using a JIS No. 5 test piece were performed. The results are shown in the material survey results in Table 3. Steel no. 3, 4 and steel no. For the steel sheets 7 and 8, micro Vickers hardness measurement was performed on the cross section in the rolling direction of the steel sheet. The test load was Steel No. 3 and 4 are 10 g, steel no. 7 and 8 were 25 g, and the measurement was continuously performed from the steel sheet surface capable of stable hardness measurement to the center of the steel sheet at a pitch of 5 μm starting from the depth of 25 μm. Steel No. The results of micro Vickers hardness measurement in FIGS. 3 and 4 are shown in FIG. The micro Vickers hardness measurement results in 7 and 8 are shown in FIG. In these FIG. 1, the horizontal axis represents the position (μm) from the steel plate surface, and the vertical axis represents the micro Vickers hardness (Hv).

  As a result, as shown in Table 3, the steel No. of the present invention. Nos. 3 and 4 do not generate St-St in the expansion process and are excellent in shape freezing property and dent resistance. Nos. 5 and 6 have a slight St-St occurrence. 7 and 8 resulted in inferior St-St generation and shape freezing property. Steel No. 1 in FIG. The micro Vickers hardness of 3 and 4 is the highest at the surface layer of 25 μm and cannot be measured, but it was assumed that a harder layer was formed from the outermost layer to the 25 μm point by the skin pass effect by temper rolling. On the other hand, a sharp decrease in hardness was observed from the 30 μm point, and the central hardness was 15 points (Hv) or more softer than the surface layer of 25 μm, and it was assumed that no strain age hardening was caused by artificial aging.

  On the other hand, Steel No. The micro Vickers hardness of Nos. 7 and 8 is Steel No. From 3 and 4, although the hardness change from the surface layer 25 μm point to the center layer was small, a slightly soft part was observed at the center of the plate thickness, but a state of uniform strain age hardening was observed. This difference in hardness distribution is considered to be a result of the combined action of the temper rolling roll diameter, rolling force, and tension. In particular, the roll diameter has a large effect on the formation of strain on the steel sheet surface. This strongly influences the formation of strain in the thickness direction of the steel, and it is assumed that their interaction is the main cause of the difference in hardness distribution.

  On the other hand, despite the production under the temper rolling conditions of the present invention, the steel No. 5 and 6 had St-St generation. Solid solution N is said to have stronger aging at room temperature than solid solution C. In Nos. 5 and 6, it is speculated that St-St was generated because the amount of solute N was larger than the amount of solute C. Based on this inference, the present inventor has obtained the steel Nos. Listed in Tables 1 to 3. By further producing 9 to 12, investigation was made on the relationship between the solid solution C and solid solution N amount of the steel sheet and the generation of St-St.

  Steel No. 9-12 is a low carbon aluminum killed steel made of a raw material and reheated to around 1100 ° C. by hot rolling, and the scraping temperature after hot rolling is set to 650-720 ° C., so that the amount of solute N is 0.0004-0.0010. %, After pickling and cold rolling, recrystallized at a continuous annealing temperature of 700 ° C., held at 400 ° C. for 60 seconds or more and over-aged, and then reduced by a 460 mm small diameter roll to a reduction rate of 2%. A dry temper rolling with a tension of 196 MPa was applied to a thickness of 0.19 mm. The solute C content of the obtained steel sheet is suppressed to 0.0010 to 0.0013% as measured by the internal friction method, and the tempering degree satisfies the material required for the reseal can at T-3. .

  As shown in Table 1, steel no. The total of the solid solution C amount and the solid solution N amount of 9 to 12 is below 20 mass ppm (hereinafter simply referred to as ppm). Nos. 9 and 10 have substantially the same amount of solute C and solute N. 11 and 12 have a quantity relationship of solid solution C ≧ solid solution N × 2. In order to confirm the St-St generation state regarding the expanding process of this steel sheet, artificial aging was performed at 170 ° C. for 7 minutes, and a 10 mm overhang test was performed by a hydraulic bulge tester. The results are shown in Table 3. Steel No. Nos. 9 and 10 show a slight St-St generation in the expanding process. 11 and 12 did not generate St-St.

FIG. 2 shows the relationship between the amount of solid solution C and solid solution N and the presence or absence of St-St after expansion processing. In FIG. 2, the horizontal axis represents the amount of dissolved C (ppm) and the vertical axis represents the amount of dissolved N (ppm). In FIG. 2, the total amount of solid solution C and solid solution N is 20 ppm or less, and the steel plate composed of the components in the shaded area having the relationship of solid solution C ≧ solid solution N × 2 is St. -Indicates that there was no occurrence of St.
Steel No. above. The findings obtained from the experimental results of 3 to 12 are summarized as follows.

(1) A steel sheet that has been temper-rolled with a small roll diameter and a low tension has a strong strain on the surface layer, but has a small strain on the inner layer and is soft, so it has excellent shape freezing properties. (2) As shown in FIG. Steel sheets having a total amount of solid solution C and solid solution N of 20 ppm or less and solid solution C ≧ solid solution N × 2 are less likely to generate St-St in the expansion process after aging. (3) On the other hand, In a steel plate having a relationship that the total amount of C and solid solution N exceeds 20 ppm or solid solution N ≧ solid solution C, St-St is likely to occur even if the surface layer has a strong strain. (4) Even when the total amount of solute N is 20 ppm or less, the steel sheet that has been subjected to temper rolling with a large diameter roll and low tension control is subjected to strain age hardening and deterioration of St-St generation and shape freezeability. (5) In addition, if the steel sheet is subjected only to continuous annealing, the yield strength after aging at 170 ° C. for 7 minutes Becomes all 320MPa or more, the dent resistance is secured.

  By obtaining such a series of experimental results, the present inventors have developed a so-called surface modification in which the St-St resistance by the expanding process and the dent resistance of the can body are subjected to a strong skin pass effect by temper rolling on the steel sheet surface layer. On the other hand, it has been found that securing the shape freezing property that guarantees the ease and accuracy of can body processing can be achieved by keeping the inner layer of the steel plate soft.

  Furthermore, as means for imparting such different material properties in the sheet thickness direction, the upper limit value of solute C and solute N is set to 20 ppm, and a small diameter roll is used and lower tension control is performed in the dry temper rolling method. It is a new finding that it can be achieved with this. Here, Steel No. 3, 4 and steel no. The reason why St-St does not occur in 11 and 12 is not clear, but there is little solid solution C and solid solution N, especially very little solid solution N, and a strong skin pass effect by temper rolling was given to the steel sheet surface layer. In this case, it is presumed that sufficient movable dislocations remain after 170 ° C. and 7 minutes of artificial aging, and the generation of St-St is suppressed.

  Next, the reason which limited the chemical component of the cold rolled steel plate for welding cans to which this invention is applied is demonstrated. In the present invention, as steel components in mass%, C: 0.015 to 0.08%, Mn: 0.10 to 0.60%, P: 0.02% or less, S: 0.02% or less, acid acceptable A steel having a composition of molten Al: 0.02-0.10% and N: 0.006% or less is used.

C: 0.015-0.08%
C is the most basic element that controls the cold-rollability and strength of steel. Generally, the strength decreases and the ductility improves as the amount of C added is reduced. When the amount of C exceeds 0.08%, the entire crystal grain size is reduced, the cold rolling property is lowered, and the strength of the welded portion is increased to cause cracking in flange processing. However, when the amount of C is less than 0.015%, the Ar3 transformation point temperature in hot rolling rises, and during hot rolling, the width end and length end of the steel sheet become less than the transformation point temperature to coarsen the crystal grains, The outermost part has a fibrous structure, and the portion where the crystal grain size becomes coarse during cold rolling is easy to extend, and conversely, the endmost part is difficult to extend. . Therefore, the C content must be limited to a range of 0.08% or less, and it is important that the C content is 0.015% or more.

Mn: 0.10 to 0.60%
Mn is an element necessary for preventing ear cracks in the hot-rolled steel sheet due to S by fixing S as MnS, and is desirably added according to the S content. In the present invention, since the S content is set to 0.02% or less for the reason described later, the lower limit of Mn is set to 0.10% accordingly. That is, the lower limit of Mn was set to 0.10% as an amount sufficient to fix 0.02% S, which is the upper limit of the S content, as MnS. On the other hand, Mn refines the crystal grain size through the action of lowering the Ar3 transformation point and thus increases the yield strength, so excessive addition is not preferable, and it is economically disadvantageous, so an upper limit of 0.60% is preferable. .

P: 0.02% or less P is an element contained as an inevitable impurity in steel, and is not an element intentionally added. If this P is excessively contained, it segregates at the grain boundaries of austenite, hardens the steel, deteriorates the rollability, and deteriorates the corrosion resistance. Therefore, the P content is preferably as low as possible. For this reason, in this invention, the upper limit of P was made into 0.02%.

S: 0.02% or less When S is excessively contained in relation to the amount of Mn, S dissolved in the hot-rolled high-temperature austenite region becomes supersaturated as the temperature decreases (Fe, Mn) as austenite grains There is a possibility that it precipitates in the boundary, and this becomes an ear crack of the hot-rolled steel sheet due to red heat embrittlement. Further, S also remains as a non-metallic inclusion and segregates at the grain boundary to lower the workability of the steel sheet and deteriorate the corrosion resistance, so the upper limit is made 0.02%.

Acid-soluble Al: 0.02-0.10%
Although Al is effective as a deoxidizing element, it reacts with N by heat treatment to become AlN, and has the effect of reducing the amount of dissolved N, Al is an important constituent element of the present invention. By specifying the amount of Al and the hot rolling heating temperature as 950 to 1100 ° C., the reprecipitation of AlN is prevented in the slab stage prior to hot rolling, and the N precipitation rate of the hot rolled sheet becomes 85% or more, at the time of canning The expansion process can improve the St-St resistance and the shape freezing property. However, if the Al content exceeds 0.10% and becomes excessive, alumina inclusions increase and the workability deteriorates, so the upper limit is made 0.10%. On the other hand, AlN is not formed with a small amount of addition, and a precipitation N ratio of 85% is not achieved, and St-St generation due to expansion processing and deterioration of shape freezing property due to hardening of the steel sheet occur. Therefore, addition of 0.02% or more is necessary.

N: 0.006% or less N is an element mixed from the air in the refining process of steelmaking. However, in the present invention, it is important to lower the solid solution N, and therefore it is desirable that the addition amount of N is smaller. . For this reason, the upper limit of the N amount is set to 0.006%. In addition, N produces strain aging in the steel sheet after temper rolling and adjusts the yield strength to improve the dent resistance of the can. Therefore, it is preferable to contain a certain amount, and in order to exert this effect, As a solid solution N, 0.0006% or more is necessary. However, if it is excessively mixed, the yield strength becomes too high and the workability deteriorates.

  In the above components, it is necessary that the solid solution N and the solid solution C have a total relationship of 10 to 20 ppm and the solid solution C ≧ the solid solution N × 2. Outside this range, the characteristics of the present invention cannot be obtained as described above.

  In addition to the components listed above, component elements generally present in known steel plates for welding cans may be included. For example, Nb: 0.001-0.003%, Ti: 0.001-0.003%, B: 0.0001-0.001%, Cu: 0.05% or less, Ni: 0.05% or less One element or two or more elements selected from Cr: 0.05% or less, Mo: 0.05% or less, and V: 0.003% or less can be contained depending on the purpose.

Nb: 0.001 to 0.003%
Nb improves toughness by making the structure finer, but if its content is less than 0.001%, the reduction of solid solution N is insufficient, so the lower limit was made 0.001%. On the other hand, when Nb is contained in an amount of 0.003% or more, the non-recrystallization temperature range in the hot rolling is expanded, and thus the yield point is increased. Therefore, the upper limit of the Nb content is set to less than 0.003%.

Ti: 0.001 to 0.003%
Ti has a strong affinity with N and precipitates as TiN during solidification, and further contributes to the refinement of the structure, thereby improving the strength and toughness, and thus improving the dent resistance of the can. For this reason, if it is less than 0.001%, the amount of TiN deposited is insufficient, and these effects cannot be exhibited, so the lower limit of the amount of Ti is set to 0.001%. On the other hand, if Ti exceeds 0.003%, the necessary amount of solute N cannot be secured, so the upper limit was made 0.003%.

B: 0.0001 to 0.001%
B has an effect of improving hardenability by adding a small amount. Further, B is an element effective for refinement of the structure and adjustment control of aging, but is combined with N to be a precipitate. Such an effect is exhibited by addition of 0.0001% or more, but if added over 0.001%, BN cannot be formed and a necessary amount of solid solution N cannot be secured. It was decided to add in the range of ˜0.001%.

Cu: 0.05% or less, Ni: 0.05% or less, Cr: 0.05% or less, Mo: 0.05% or less These elements all increase the strength of the steel sheet and thus the dent resistance of the can. And added as needed. However, if added over 0.05%, the rollability is deteriorated, and the steel plate is hardened more than necessary, and the can-making processability is deteriorated, so the upper limit was made 0.05%. .

V: 0.003% or less V is a carbonitride-forming element, and is generally used to adjust the microstructure, C content, and N content of steel materials. Since the amount is small, the upper limit was set to 0.003% by following this.

  Then, the hot rolling process of this invention is demonstrated. The steel containing the above-mentioned components, the balance being Fe, and inevitable impurities, is cooled to 700 ° C. or lower as a continuous cast slab, and most of the solid solution N in the slab is fixed as AlN precipitates. Next, the slab after the precipitation treatment is reheated to 950 to 1100 ° C. The reason for reheating to this temperature range is to prevent the precipitated AlN from decomposing and re-dissolving, so that the precipitation N ratio is 85% or more. On the other hand, the lower limit of the reheating temperature needs to be 950 ° C. which does not hinder hot rolling work.

  Next, it is hot-rolled at a finishing temperature of Ar 3 to 950 ° C. and scraped off in a temperature range of 650 to 720 ° C. The finishing temperature is set at Ar3 or higher to suppress the austenite-ferrite transformation during rolling to stabilize hot rolling, but when it exceeds 950 ° C., the hot rolled work roll becomes rough and the product becomes rough. Since the surface defect of the film is generated and the roll life is shortened, the upper limit is limited to 950 ° C. The lower limit of the scraping temperature is set to 650 ° C. in order to secure the N precipitation rate of 85% or more in the width / longitudinal direction of the hot-rolled sheet. On the other hand, the upper limit is set to 720 ° C. This is to suppress the deterioration of the workability and corrosion resistance of the steel sheet.

  Then, the annealing process of this invention is described. The hot-rolled sheet obtained as described above is pickled, cold-rolled, and continuously annealed. The reason why the annealing soaking temperature is set to 650 ° C. or more is to improve the workability of the steel sheet by recrystallization and grain growth. On the other hand, the upper limit was set to 720 ° C. because carbides aggregate during annealing to deteriorate workability and corrosion resistance, and in-furnace drawing tends to occur during continuous annealing.

  The lower limit of the soaking time is 10 seconds because it is an indispensable time for recrystallization and grain growth. On the other hand, if the holding time exceeds 60 seconds, it hardly contributes to grain growth. The upper limit was set to 60 seconds.

  The overaging temperature is desirably 300 to 500 ° C., and when the temperature is lower than 300 ° C., it takes a long time for solute C precipitation, so the lower limit is regulated. On the other hand, when the temperature is higher than 500 ° C., the amount of C dissolved in a balanced manner increases and sufficient solid solution C remains to generate St—St on the steel sheet, so the upper limit is regulated to 500 ° C. did.

  Then, the temper rolling process of this invention is described. In the present invention, temper rolling is performed on the steel sheet after continuous annealing. As the rolling conditions, a skin pass effect with a rolling reduction of 1.5 to 3.0% is applied to the steel sheet with a work roll having a roll diameter of 470 mm or less. The roll diameter is set to 470 mm or less in order to suppress the deterioration of St-St resistance by leaving movable dislocations on the steel sheet even when subjected to severe aging at 170 ° C. and 7 minutes, unlike normal aging at normal temperature. It is. If the rolling reduction is lower than 1.5%, St-St is generated, and thus the reduction is regulated. On the other hand, in dry temper rolling, it is difficult to apply a rolling reduction of 3.0% or more to the steel sheet, and excessive hardening of the steel sheet surface layer deteriorates can workability, so the upper limit was made 3.0%.

  The tension during temper rolling was 50 to 200 MPa. When the tension exceeds 200 MPa, a cold-rolled structure is generated, and the shape freezing property and the expand moldability are lowered. On the other hand, if it is less than 50 MPa, the plate passing property and the rollability are lowered, resulting in poor shape and workability.

  The steel plate for cans of the present invention is usually subjected to surface treatment and shipped to a can maker. Although it does not specifically limit as a surface treatment layer, The plating layer containing at least 1 or more types of nickel, tin, chromium, zinc, aluminum, etc. can be used. Or it can have a film laminate layer on at least one side.

  The present invention will be specifically described below with reference to examples. Steel components listed in Table 1 were melted in a converter, and after adjusting the main components, steel was produced as low-carbon aluminum killed steel, and slabs were formed using a continuous casting machine. This slab was heated under the hot rolling conditions shown in Table 2 and hot rolled and scraped to form a hot rolled coil containing a small amount of solute N. Next, after descaling with hydrochloric acid pickling, a thin cold-rolled coil was formed with a 6-stand tandem cold-roller, and then recrystallization annealing was performed with a continuous annealing machine with an overaging treatment, so that a small amount of solid solution C An annealing coil having

  Steel No. for comparison was used. 1 and 2 are box-annealed after continuous annealing to form non-aged steel sheets in which the solid solution C and N are extremely reduced. On the other hand, in Comparative Examples 5 to 10, the addition amount of Al is reduced or the addition amount of N is reduced. The amount of precipitation N of the hot rolled coil was made to be less than 85% by increasing the amount of the hot rolled coiling temperature slightly lower. On the contrary, in Examples 3, 4 and 11, 12 of the present invention, precipitation of hot-rolled coils was achieved by increasing the amount of Al added or decreasing the amount of N added, and further increasing the hot-rolling temperature. It manufactured so that N rate might be 85% or more.

  The temper rolling is performed using steel No. Nos. 5 and 6 were subjected to temper rolling using a large-diameter roll and high tension, and a small-diameter roll and low tension were applied to the others.

The temper-rolled steel sheet is pretreated with alkali washing and sulfuric acid washing, and a Ni plating layer of 650 to 750 mg / m ² is formed in the lower layer with a watt bath as a plating solution, and then the upper layer is 5 in a chromate bath. Multi-layer plating consisting of 10 mg / m ² Cr plating was applied.

  The plated steel plate was baked at 170 ° C. for 7 minutes, which is a heat treatment condition for the film-laminated steel plate. Table 3 lists the materials obtained by taking samples from the above Cr—Ni multilayer plated steel plates and baking them.

  As is apparent from Table 3, the steel sheet according to the present invention has improved Stability and Dent resistance as well as improvement in shape freezing property and expand formability remaining in a continuously annealed steel sheet made of the conventional low carbon aluminum killed steel. Thus, a steel plate for a resealable can be produced that takes advantage of the properties of “soft during processing and easily increased in yield strength in the heat treatment after forming the can body”.

It is a figure which shows the Vickers hardness distribution of the steel plate thickness direction after 170 degreeC and the artificial aging for 7 minutes. It is a figure which shows the relationship between the solid solution C of this invention steel plate, the amount of solid solution N, and St-St generation | occurrence | production.

Claims (4)

  Precipitation N ratio (NasAlN × 100 / total N) is 85% or more, and after heat holding at 170 ° C. for 7 minutes, the hardness at the depth of 25 μm in the thickness direction from the steel plate surface, and the hardness at the center in the thickness direction of the steel plate Is a cold-rolled steel sheet for welding cans, characterized in that the difference is 15 points or more in micro Vickers hardness. As a steel component in mass%,
C: 0.015-0.08%,
Mn: 0.10 to 0.60%,
P: 0.02% or less,
S: 0.02% or less,
Acid-soluble Al: 0.02-0.10%
N: 0.006% or less, the balance being Fe and inevitable impurities, the total of solid solution N and solid solution C contained in the steel sheet is 10 to 20 ppm, and solid solution C ≧ solid solution N × The cold-rolled steel sheet for welding cans according to claim 1, wherein: As a further steel component,
Nb: 0.001 to 0.003%,
Ti: 0.001 to 0.003%,
B: 0.0001 to 0.001%,
Cu: 0.05% or less,
Ni: 0.05% or less,
Cr: 0.05% or less,
Mo: 0.05% or less,
The cold-rolled steel sheet for a welding can according to claim 2, comprising one or more elements selected from V: 0.003% or less.   The continuous cast slab of the component according to claim 2 or 3 is once cooled to 700 ° C or lower, then inserted into a hot rolling furnace and reheated to 950 to 1100 ° C, and then the finishing temperature is set at Ar3 point to 950 ° C. , After hot rolling at 650 to 720 ° C., pickling and cold rolling, holding at a soaking temperature of 650 to 720 ° C. for 10 to 60 seconds, cooling to 500 ° C. or lower, and 300 to 500 ° C. Cold annealing for welding cans, characterized by performing continuous annealing for 60 seconds or more and then performing temper rolling with a roll having a roll diameter of 470 mm or less at a rolling reduction of 1.5 to 3.0% and a tension of 50 to 200 MPa. A method for producing rolled steel sheets.