JP3309732B2 - Cold-rolled steel sheet for direct single enamel with excellent deep drawability and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold-rolled steel sheet for directly enamelling which has excellent workability, especially deep drawability, and a method for producing the same.

[0002]

2. Description of the Related Art Enamel products are widely used in kitchen utensils, building materials, sinks, etc., but when they are used as materials for bathtubs, pots, washstands, etc. Excellent deep drawability is required. Conventionally, for such applications, Ti-added steel sheets and B-added aluminum killed steel sheets have been used.
The enamel conditions that can be directly applied once are very narrow,
Since it is difficult to manage by an enamel maker, it is hardly used for direct single use.

[0003] In the case of directly applying enamel once, it is necessary to make the pickling weight loss and the Ni adhesion amount equal to or more than certain values in order to secure the enamel adhesion. If the amount is too large, there is a problem that enamel defects such as bubbles and black spots are easily generated.

Further, in the steps of pickling, (hot water washing), water washing, and Ni-dip, which are performed as enamel pretreatment, Ni-dip is applied as the operation proceeds with water brought in from a washing tank.
The pH value of the liquid tends to increase. As a result, Ni is likely to adhere to the steel sheet in a plate shape, and it becomes difficult for the interface between the enamel layer and the steel sheet to have irregularities during firing of the enamel, which causes a decrease in the adhesion of the enamel layer.

[0005] Furthermore, bubbles generated at the interface between the Ni coating layer and the steel sheet are difficult to escape into the enamel layer, and the bubbles reach the surface of the enamel layer. As a result, bubble defects and black spot defects are likely to occur. Since these enamel defects are greatly affected by the dew point at the time of firing the enamel, etc., a steel sheet for enamel is insensitive to these factors.

[0006] In addition, in the enamel maker, direct enameling is applied once from the viewpoints of streamlining the process and thermal shock resistance. For these reasons, there is a strong demand for an enameled steel sheet which is excellent in workability and can be directly applied once.

[0007]

As an enameled steel sheet that can be directly hung once, conventionally, carbon and nitrogen in the steel have been reduced as much as possible in the steel making stage, and steel that has not been deoxidized (hereinafter referred to as "deoxidized steel") has been used. High oxygen steel) is widely used. However, in the case of the above-described high oxygen steel, workability and aging resistance are inferior due to the presence of solid solution carbon and solid solution nitrogen in the steel, and the above-mentioned required performance must be sufficiently satisfied. Can not.

As measures for improving aging resistance, for example, Japanese Patent Application Laid-Open No.
And the like are disclosed. However, the above-mentioned steel sheet in which Ti, Nb or the like is added to the steel has improved workability, but particularly when the dew point is high, black spots and bubble defects are likely to be generated. Cannot be applied for hanging. Further, in the steel sheet disclosed in JP-A-63-277742, since the amount of oxygen is relatively small, under severe conditions, nail jump defects may occur.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems, and to provide a cold-rolled steel sheet for enamel directly having excellent deep drawability, having both workability, particularly deep drawability and enamel direct once-applying property. And a method for manufacturing the same.

[0010]

SUMMARY OF THE INVENTION From the above-mentioned viewpoints, the present inventors have intensively studied to develop a cold-rolled steel sheet for direct enamelling having excellent deep drawability. As a result, they have found that the addition of an appropriate amount of chromium is effective in improving the workability of high oxygen steel without directly impairing the single-stroke characteristics. That is, an appropriate amount of chromium combines with manganese and oxygen in steel to have an effect of improving workability, particularly deep drawability.

It has also been found that, in order to improve the aging resistance without directly impairing the single-stroke characteristics, it is effective to further add an appropriate amount of boron. Boron has an effect of improving aging resistance by combining with carbon and nitrogen in steel.

Further, a slab containing the above-mentioned appropriate amount of chromium and, if necessary, containing an appropriate amount of boron is hot-rolled at a specific finishing temperature, cold-rolled at a specific rolling reduction, and It has been found that deep annealing can be further improved by annealing at a specific heating rate.

The present invention has been made based on the above findings, and the invention according to claim 1 is characterized in that carbon (C): 0.0030 wt.% Or less, silicon (Si): 0.05 wt. Mn): 0.20 to 0.40 wt.%, Phosphorus (P): 0.005 to 0.025 wt.%, Sulfur (S): 0.005 to 0.030 wt.% , Soluble aluminum (Sol.Al): 0.010 wt.% Or less, oxygen ( O): 0.0450 to 0.1000 wt.%, Copper (Cu): 0.020 to 0.050 wt.%, Nitrogen (N): 0.0030 wt.% Or less, Chromium (Cr): 0.5 to 1.3 of oxygen (O) amount, remaining: It is characterized by being composed of iron (Fe) and unavoidable impurities. The invention according to claim 2 is characterized in that carbon (C): 0.0030 wt.% Or less, silicon (Si): 0.05 wt.% Or less, manganese (Mn) ): 0.20 to 0.40 wt.%, Phosphorus (P): 0.005 to 0.025 wt.%, Sulfur (S): 0.005 to 0.030 wt.% , Soluble aluminum (Sol.Al): 0.010 wt.% Or less, oxygen (O) ): 0.0450 to 0.1000 wt.%, Copper (Cu): 0.020 to 0.050 wt.%, Nitrogen (N): 0.0030 wt.% Or less, Chromium (Cr): It is characterized by being composed of 0.5 to 1.3 of oxygen (O), boron (B): 0.0010 to 0.0050 wt.%, And the balance: iron (Fe) and unavoidable impurities .

The invention according to claim 3 has the chemical component composition according to claim 1 or 2, and has a finishing temperature of hot rolling of 860 to 900 ° C. and a rolling reduction of cold rolling of 70% or more. Heating rate during annealing: 5 ° C./sec or more, characterized by being manufactured under rolling and annealing conditions.

Further, in the method for producing a cold rolled steel sheet for directly enamelling of the present invention according to claim 4, the slab having the chemical composition is hot-rolled at a finishing temperature of 860 to 900 ° C. This is rolled up to prepare a hot-rolled steel sheet, and then the hot-rolled steel sheet is cold-rolled at a rolling reduction of 70% or more to prepare a cold-rolled steel sheet. It is characterized by annealing at a heating rate.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the chemical composition of the cold-rolled steel sheet for enamel according to the present invention to the above-mentioned ranges will be described below. (1) Carbon (C) and nitrogen (N): Carbon and nitrogen impede the formation of a preferred texture by the composite oxide of Mn and Cr, which is the main object of the present invention, and deteriorate the workability of the steel sheet. Further, when the amounts of carbon and nitrogen are too large, the aging resistance is deteriorated, and when the amount of carbon is too large, the black spot resistance is deteriorated. Therefore, it is desirable that the contents of carbon and nitrogen be as small as possible.
The carbon content is limited to 0.0030 wt.% Or less, and the nitrogen content is
It was limited to 0.0030 wt.% Or less. (2) Silicon (Si): When melting steel, silicon is added as necessary in order to adjust the amount of oxygen in the steel. However, in order to improve the surface properties of the steel sheet, it is better that the silicon content is small. If the silicon content exceeds 0.05 wt.%, Surface defects related to the Si scale are likely to occur. Therefore, the silicon content is 0.05w
Should be limited to t.% or less. (3) Soluble aluminum (Sol.Al): Aluminum is added as needed to control the amount of oxygen in steel when smelting steel. However, when the content of soluble aluminum exceeds 0.010 wt.%, Sol. Al is combined with nitrogen in the steel to form fine AlN, which significantly deteriorates the workability of the steel sheet. Therefore, the content of soluble aluminum should be limited to 0.010 wt.% Or less.
It is. (4) Manganese (Mn): Manganese combines with oxygen in steel to form MnO, which acts as a trap site for hydrogen entering during enamel sintering and improves nail fly resistance. ,
It has the effect of forming a composite texture with chromium to form a texture preferred for deep drawability. However, if the manganese content is less than 0.20 wt.%, The above-mentioned effects cannot be obtained. On the other hand, the manganese content is 0.40 wt.
%, The workability of the steel sheet is deteriorated. Therefore, the manganese content should be limited to the range of 0.20 to 0.40 wt.%. (5) Chromium (Cr): Chromium is the most important element in the present invention, and has the effect of improving workability and nail fly resistance. Further, chromium combines with manganese and oxygen in steel to contribute to the improvement of deep drawability. Therefore, the amount of chromium needs to be adjusted according to the amount of oxygen in the steel. If the chromium content is less than 0.5 times the oxygen content in the steel, the above-mentioned effects cannot be obtained. On the other hand, if the chromium content exceeds 1.3 times the oxygen content in the steel, the amount of dissolved Cr increases,
Deteriorates workability of steel sheet. Therefore, the chromium content is
It should be limited to a range of 0.5 to 1.3 times the amount of oxygen in the steel. (6) Oxygen (O): Oxygen combines with manganese and iron in steel to form an oxide, acts as a trap site for hydrogen entering during enamel firing, and has the effect of improving nail fly resistance. are doing. Further, part of oxygen combines with chromium and manganese in steel to form an oxide, which contributes to improvement in deep drawability.
However, if the oxygen content is less than 0.0450 wt.%, The above-mentioned effects cannot be obtained. On the other hand, if the oxygen content exceeds 0.1000 wt.%, The workability of the steel sheet deteriorates. Therefore, the oxygen content should be limited to the range of 0.0450-0.1000 wt.%. From the viewpoint of processability, the preferred content of oxygen is in the range of 0.0450 to 0.0700 wt.%.

When chromium is added to the steel as in the steel sheet of the present invention, the loss in pickling during pickling in the enamel pretreatment becomes large.
It is necessary to adjust the contents of sulfur and copper to ensure adhesion, black spot resistance and foam resistance. (7) Phosphorus (P): Phosphorus greatly affects the pickling weight loss value and affects the adhesion of the enamel. That is, the phosphorus content is 0.005w
If it is less than t.%, the pickling rate is too slow, and a sufficient pickling weight loss value cannot be obtained under ordinary pickling conditions. On the other hand, the phosphorus content is 0.025w
If the amount exceeds t.%, the pickling weight loss value becomes too large, and bubbles and black spot defects are likely to occur, for example, when the dew point during firing is high. Therefore, the phosphorus content should be limited to the range of 0.005 to 0.025 wt.%. (8) Sulfur (S): Sulfur has the effect of increasing the pickling weight loss value and affects the adhesion of the enamel. However, if the sulfur content is less than 0.005 wt.%, The above-mentioned effects cannot be obtained. On the other hand, the sulfur content is 0.
If it exceeds 030 wt.%, Workability will deteriorate. Therefore, the sulfur content should be limited to the range of 0.005 to 0.030 wt.%. (9) Copper (Cu): Copper has the effect of increasing the unevenness between the enamel layer and the steel sheet interface during enamel firing and improving the enamel adhesion. However, the copper content is 0.020
If the amount is less than wt.%, good adhesion cannot be produced under ordinary enamel conditions. On the other hand, copper has the effect of reducing the pickling rate during enamel pretreatment, so if the copper content exceeds 0.050 wt.%, The pickling weight loss value becomes too small, and under normal enamel conditions. , Good adhesion cannot be obtained. Therefore, the copper content is 0.020 to 0.050 wt.%
Should be limited within the range. Incidentally, a preferable copper content for obtaining extremely good adhesion is 0.025 to 0.040 wt.
It is within the range of%. (10) Boron (B): Boron combines with nitrogen in steel to improve the aging resistance of the steel sheet. Therefore,
If necessary, it is additionally contained in steel. However,
If the boron content is less than 0.0010 wt.%, Most of the oxides are oxides, so that the above effects cannot be obtained. On the other hand, if the boron content exceeds 0.0050 wt.%, The workability of the steel sheet deteriorates. Therefore, when boron is added, its content should be limited to the range of 0.0010 to 0.0050 wt.%.

Other than the above-mentioned elements, the balance, iron and
It is an unavoidable impurity. In order to make the effect of chromium in the present invention remarkable, Nb, Ta, W and Mo are
Not intentionally added.

The cold-rolled steel sheet for enamel according to the present invention has the above-mentioned chemical composition and has a finishing temperature of hot rolling of 860 to 900 ° C. and a rolling reduction of cold rolling of 70 as described below. % Or more, and a heating rate during annealing: preferably 5 ° C./sec or more under rolling and annealing conditions. Thereby, the workability of the steel sheet can be further improved.

Next, a method for producing the steel sheet of the present invention will be described. A slab of steel having a chemical composition within the scope of the invention described above is prepared. If such a slab is prepared by a steel ingot method, coarse inclusions are likely to be present between the rim layer and the core portion, and blistering defects are likely to occur after enamelling. Therefore, it is preferable to cast the slab by the continuous casting method.

After cooling the continuously cast slab, it is heated and hot-rolled, or the slab is directly hot-rolled without heating to prepare a hot-rolled steel strip. However, when the steel contains boron in an amount within the range of the present invention, in order to suppress the solid solution of BN due to heating,
Preferably, the heating temperature is 1200 ° C. or less. The slab after casting does not need to be cooled to room temperature, and may be heated after BN is precipitated.

In the hot rolling, the finish rolling temperature is set at 860 to 860.
The temperature is preferably within the range of 900 ° C. By performing finish rolling at a temperature of 860 ° C. or higher, that is, a temperature of the Ar ₃ transformation point or higher, ferrite grains in the hot-rolled steel strip are refined, and workability of the steel strip is improved. On the other hand, when the finish rolling temperature exceeds 900 ° C., ferrite grains grow, and conversely, there arises a problem that workability of the steel strip deteriorates.

The steel strip finish-rolled in hot rolling is
The film is wound by a conventional method. The winding temperature at this time is 60 ° C from the viewpoint of workability and pickling properties after hot rolling.
It is preferable that the temperature be in the range of 0 to 700 ° C. In addition, even if the rough rolling in the hot rolling is omitted and the thin slab continuously cast is directly finish-rolled, the effect of the present invention is not impaired. The hot-rolled steel strip obtained as described above is pickled and then cold-rolled. The rolling reduction at the time of cold rolling is preferably 70% or more from the viewpoint of workability.

Next, the cold-rolled cold-rolled steel strip is annealed. The method of annealing the cold-rolled steel strip is not particularly limited, and may be any of the well-known box annealing method (tight coil annealing method), open coil annealing method, and continuous annealing method. However, for applications requiring particularly excellent deep drawability, annealing at a temperature of 800 ° C. or higher at a heating rate of 5 ° C./second or higher is preferable. Although the reason is not clear, it is presumed that if the heating rate is slow at less than 5 ° C./sec, the concentrated solid solution C and solid solution N diffuse in the vicinity of the oxide and hinder the growth of crystal grains. Is done. Further, the higher the annealing temperature, the more the growth of ferrite grains is promoted and the better the workability. The annealed steel strip can be used as a product as it is, but if necessary, may be temper rolled at an elongation of 2.0% or less.

[0025]

【Example】

[Embodiment 1] Next, the present invention will be described with reference to an embodiment in comparison with a comparative example.

Each of the steel of the present invention having a chemical composition within the range of the present invention shown in Table 1 and a comparative steel having at least one of the chemical compositions shown in Table 2 outside the range of the present invention were melted. And slabs were prepared by continuous casting. The slabs of the steel of the present invention and the comparative steel are heated to a temperature of 1200 ° C., then hot-rolled at a finishing temperature of 890 ° C., wound around a coil at a temperature of 620 ° C., and hot-rolled with a thickness of 2.8 mm. A band was prepared.

Next, after pickling the obtained hot-rolled steel strip,
Cold rolling was performed at a rolling reduction of 75% to prepare a cold-rolled steel strip having a thickness of 0.7 mm. The obtained cold rolled steel strip was continuously annealed at a temperature of 850 ° C. at a heating rate of 7 ° C./sec, and then subjected to a 1.0% temper rolling. Thus, the cold-rolled steel sheet for enamel according to the present invention (hereinafter referred to as the present steel sheet) No. 1 to 20 shown in Table 1 and the cold-rolled steel sheet for enamel for comparison (hereinafter referred to as comparative steel sheet) No. 1 shown in Table 2 1 to 11 were prepared.

[0028]

[Table 1]

[0029]

[Table 2]

From each of the steel sheet of the present invention and the steel sheet for comparison, a JIS No. 5 test piece was sampled from the rolling direction and subjected to a tensile test. Further, from each of the steel sheet of the present invention and the steel sheet for comparison, a JIS No. 5 test piece was sampled from the rolling direction, the direction at 45 degrees from the rolling direction and the direction perpendicular to the rolling direction, and the Rankford value (mean r value) was measured. did. The average r value is a value calculated by the following equation.

Average r value = (r value in the rolling direction + 2 × r value in the rolling direction and 45 ° + r value in the direction perpendicular to the rolling direction) / 4
An enamelling was performed, and the enamel properties, ie, adhesion, nail flying resistance and black spot resistance were examined. In addition, the adhesion test
It is difficult to obtain good adhesion, short sulfuric acid pickling time and Ni-d
IP time was short. The nail fly resistance test was carried out under conditions in which nail fly is likely to occur, the sulfuric acid washing time is short, the Ni-dip time is short, and the dew point during firing is high. The black spot resistance test was performed under the conditions that black spots are easily generated, the sulfuric acid washing time is short, the Ni-dip time is long, and the dew point during firing is high. (1) Adhesion test a. Enameling Conditions Pretreatment: Degreasing → sulfate pickling _{(15% H 2 SO 4 ·} 70 ℃ × 15min) →
_{Ni-dip (NiSO 4 · 7H} 2 O: 13g / l, pH: 3.5, 70 ℃ × 3mi
n) Glaze: 1553C glaze made by Nippon Ferro, target: each side
100 µm firing: 830 ° C x 2 min, b. Test conditions The enamel adhesion was measured by the PEI method for ten test pieces (100 × 100 mm) directly enameled under the above enameling conditions. (2) Nail fly resistance test a. Enameling Conditions Pretreatment: Degreasing → sulfate pickling _{(15% H 2 SO 4 ·} 70 ℃ × 2min) →
_{Ni-dip (NiSO 4 · 7H} 2 O: 13g / l, pH: 3.5, 70 ℃ × 2mi
n) Glaze: 1553C glaze made by Nippon Ferro, target: each side
100 µm firing: 830 ° C x 2min (humidified atmosphere, DP: 30 ° C) b. Test conditions Ten nails (100 × 100 mm), which were directly enameled once under the above enamelling conditions, were observed for the occurrence of nail jumping, and at least one nail jump was observed on both sides of each test piece. The object was regarded as a nail jump occurrence, and the occurrence ratio was examined to determine the nail jump occurrence ratio.

(3) Black spot resistance test: a. Enameling Conditions Pretreatment: Degreasing → sulfate pickling _{(15% H 2 SO 4 ·} 70 ℃ × 15min) →
_{Ni-dip (NiSO 4 · 7H} 2 O: 13g / l, pH: 3.5, 70 ℃ × 10mi
n) Glaze: 1553C glaze made by Nippon Ferro, target: each side
100 µm firing: 830 ° C x 2min (humidified atmosphere, DP: 30 ° C) b. Test conditions Observation was made on the appearance of black spots on 10 test pieces (100 × 100 mm) directly enamelled under the above enamelling conditions, and bubbles and black spots on the front and back of each test piece were of practically bad degree. The occurrence rate of black spots was determined as the occurrence of black spots, and the occurrence rate was determined as the black spot occurrence rate.

Further, the mechanical properties of the steel sheet of the present invention and the comparative steel sheet, namely, YS (yield strength), TS (tensile temperature), El (elongation), rm (average r value), and AI (strain aging index) ).

Table 3 shows the mechanical properties of the steel sheet of the present invention and the comparative steel sheet, ie, YS, TS, El, rm, and the enamel properties, ie, adhesion, black spot generation rate and nail jump generation rate evaluated by the above.

[0035]

[Table 3]

As is clear from Tables 1, 2 and 3, a comparative steel sheet having a high C content in the steel beyond the scope of the present invention.
No. 1 was inferior in workability, aging resistance and black spot resistance. Comparative steel sheet No. 2 having a large Mn content beyond the scope of the present invention
Was inferior in workability. Comparative steel sheet No. 3 having a large P content exceeding the range of the present invention was inferior in workability and black spot resistance. Comparative steel sheet N having a high S content beyond the scope of the present invention
o.4 was inferior in workability. Comparative steel sheet No. 5 having a large N content exceeding the range of the present invention was inferior in workability and aging resistance.

Comparative steel sheet No. 6 having an O content outside the range of the present invention and having a small O content had nail jumping and poor nail jump resistance.
Comparative steel sheet No. 7 having a large amount of Cu outside the scope of the present invention
The adhesiveness was deteriorated. Comparative steel sheet No. 8 having a small amount of Cr outside the range of the present invention and comparative steel sheet No. 9 having a large amount of Cr exceeding the range of the present invention had poor deep drawability. The comparative steel sheet No. 10 in which the amount of B was larger than the range of the present invention had poor workability. And the comparative steel plate No. 11 in which Ti was added to the steel had poor black spot resistance.

On the other hand, the steel sheets Nos. 1 to 20 of the present invention
All of them are excellent in processability and enamel, especially
In the steel sheets Nos. 17 to 20 of the present invention to which chromium was added, the aging resistance was improved without deterioration in workability.

Example 2 A steel having the chemical composition shown in Table 4 was smelted with steel in which chromium was added within the range of 0.2 to 1.6 in oxygen content, and formed into a slab by continuous casting. Prepared. After heating the above slab to a temperature of 1180 ° C, 890
A hot-rolled steel strip having a thickness of 2.8 mm was prepared by hot rolling at a finishing temperature of 200 ° C. and winding around a coil at a temperature of 620 ° C.

[0040]

[Table 4]

Next, after pickling the obtained hot-rolled steel strip,
Cold rolling was performed at a rolling reduction of 75% to prepare a cold-rolled steel strip having a thickness of 0.7 mm. The obtained cold-rolled steel strip was continuously annealed at a temperature of 850 ° C. at a heating rate of 5 ° C./sec, and then subjected to a temper rolling of 1.0% to prepare a cold-rolled steel sheet for enamel.

A JIS No. 5 test piece was sampled from each of the above-mentioned cold rolled steel sheets for enamel from the rolling direction, the direction at 45 degrees from the rolling direction, and the direction perpendicular to the rolling direction, and the Rankford value (mean r value) was measured. The formula for calculating the average r value is as described above.

FIG. 1 is a graph showing the relationship between the chromium content in steel and the average r value. As is clear from FIG.
The average r value of the test pieces having a chromium content in the range of 0.5 to 1.3 of the oxygen content was high, and the deep drawability was improved.

Example 3 A steel having the chemical composition shown in Table 5 was prepared by melting a steel in which boron was added in an amount of 0.008 wt.% Or less to obtain a slab by a continuous casting method. The slab was heated to a temperature of 1180 ° C., hot-rolled at a finishing temperature of 880 ° C., wound around a coil at a temperature of 635 ° C., and a hot-rolled steel strip having a thickness of 3.2 mm was prepared.

[0045]

[Table 5]

Next, after pickling the obtained hot-rolled steel strip,
Cold rolling was performed at a rolling reduction of 75% to prepare a cold-rolled steel strip having a thickness of 0.8 mm. Next, the obtained cold-rolled steel strip was continuously annealed at a temperature of 850 ° C. at a heating rate of 7 ° C./sec.
Was subjected to temper rolling to prepare a cold-rolled steel sheet for enamel.

From the rolling direction of the above cold rolled steel sheet for enamel, JI
S No. 5 test piece was sampled and subjected to a tensile test and an aging test to obtain an elongation value (El value) and a strain aging index (AI value).
I asked. In the aging test, the amount of increase in the descending yield point after aging treatment at 100 ° C. for 1 hour after 8% prestrain was determined as AI (Aging Index).

FIG. 2 is a graph showing the relationship between the boron content in steel, the El value and the AI value. In FIG. 2, a circle indicates an El value, and a triangle indicates an AI value. As is clear from FIG. 2, the boron content is 0.0010 to 0.0050 w.
Test pieces in the range of t.% had a high El value and an appropriate AI value, and had improved aging resistance without impairing workability.

Example 4 Steel having a chemical composition within the range of the present invention shown in Table 6 was melted and prepared into a slab by a continuous casting method. This slab was heated to a temperature of 1190 ° C., hot-rolled at various finishing temperatures shown in Table 6, wound around a coil at a temperature of 635 ° C., and a hot-rolled steel strip having a thickness of 3.2 mm was prepared. After pickling the obtained hot-rolled steel strip, it was cold-rolled at various rolling reductions shown in Table 6. Next, the obtained cold-rolled steel strip was continuously annealed at various heating rates shown in Table 6, and then 1.2
% Temper rolling. A JIS No. 5 test piece was sampled from each of the steel sheets Nos. 21 to 40 of the present invention thus obtained, and the Rankford value (average r value) was measured. Table 6 also shows the measurement results.

[0050]

[Table 6]

As is apparent from Table 6, the finishing temperature in the hot rolling, the rolling reduction in the cold rolling, and the heating rate during the annealing are all within the scope of the present invention described in claim 3. Steel plate No. 24, 25, 26, 34, 35, 3
In No. 6, a particularly high average r value was obtained.

[0052]

As described above, according to the present invention,
An industrially superior effect is obtained in which a cold-rolled steel sheet for direct single enamel having excellent workability, particularly deep drawability, and direct enamel direct application is obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of chromium and the average r value.

FIG. 2 is a graph showing the relationship between the amount of boron and El and AI values.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-7-166296 (JP, A) JP-A-8-27522 (JP, A) JP-A-8-13081 (JP, A) JP-A 8- 13089 (JP, A) JP-A-51-20717 (JP, A) JP-A-6-128687 (JP, A) JP-A-63-243225 (JP, A) JP-B-58-56023 (JP, B1) (58) Field surveyed (Int.Cl. ⁷ , DB name) C22C 38/20 C21D 8/04 C21D 9/48 C22C 38/00 301 C22C 38/32

Claims (4)

(57) [Claims] 1. Carbon (C): 0.0030 wt.% Or less, silicon (Si): 0.05 wt.% Or less, manganese (Mn): 0.20 to 0.40 wt.%, Phosphorus (P): 0.005 to 0.025 wt.% , Sulfur (S): 0.005 to 0.030 wt .%, Soluble aluminum (Sol . Al): 0.010 wt.% Or less, Oxygen (O): 0.0450 to 0.1000 wt.%, Copper (Cu): 0.020 to 0.050 wt.% Nitrogen (N): 0.0030 wt.% Or less, Chromium (Cr): Oxygen (O) 0.5-1.3, and the rest: Iron (Fe) and unavoidable impurities , deep drawability Excellent cold rolled steel sheet for direct enamelling. 2. Carbon (C): 0.0030 wt.% Or less, silicon (Si): 0.05 wt.% Or less, manganese (Mn): 0.20 to 0.40 wt.%, Phosphorus (P): 0.005 to 0.025 wt.% , Sulfur (S): 0.005 to 0.030 wt .%, Soluble aluminum (Sol . Al): 0.010 wt.% Or less, Oxygen (O): 0.0450 to 0.1000 wt.%, Copper (Cu): 0.020 to 0.050 wt.% , Nitrogen (N): 0.0030 wt.% Or less, Chromium (Cr): Oxygen (O) 0.5 to 1.3, Boron (B): 0.0010 to 0.0050 wt.%, And the rest: Iron (Fe) and inevitable A cold-rolled steel sheet for enamelling directly, having excellent deep drawability, characterized by being composed of impurities . 3. The hot-rolling finishing temperature: 860 to 900 having the chemical component composition according to claim 1 or 2.
, Cold rolling: reduction rate: 70% or more, heating rate during annealing: 5 ° C / sec or more, manufactured under rolling and annealing conditions. Cold rolled steel sheet. 4. A slab having the chemical composition according to claim 1 is prepared, and the slab is subjected to 860 to 900.
Hot-rolling at a finishing temperature in the range of 0 ° C. to prepare a hot-rolled steel sheet, and then cold-rolling the hot-rolled steel sheet at a rolling reduction of 70% or more to prepare a cold-rolled steel sheet, A method for producing a cold-rolled steel sheet for direct enamelling with excellent deep drawability, wherein the cold-rolled steel sheet is annealed at a heating rate of 5 ° C./sec or more.