JPH116031A - Cold-rolled steel sheet for enamel which has excellent workability and is hard to be softened during enamel firing and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold-rolled steel sheet for enamel which is excellent in workability and hardly softens at the time of firing the enamel, while maintaining good enamel properties. SOLUTION: In weight%, C: 0.005% or less, S
i: 0 to 0.05%, Mn: 0.2 to 0.7%, P:
0.004 to 0.025%, S: 0 to 0.025%, s
ol. Al: 0 to 0.01%, O: 0.045 to 0.1
%, Cu: 0.02-0.05%, N: 0.005% or less, Nb: 0.01-0.1%, and 0.5O-
By containing 2.5O of Cr, a cold-rolled steel sheet for enamel is obtained which has excellent workability and is hard to be softened during enamel firing.

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 enamel which has excellent workability and is hard to be softened during enamel firing and a method for producing the same.

[0002]

2. Description of the Related Art Enamel products are used in kitchen utensils, building materials, sinks, and the like. From the viewpoint of improving enamel properties such as nail jump resistance, steel for enamels is manufactured by reducing C and N in the steel as much as possible at the steelmaking stage and manufacturing without deoxidation (hereinafter referred to as high oxygen steel). Is used.

[0003] In pots, kettles, and the like, excellent workability is required for enameled steel sheets. For such uses, pictures and patterns are often baked from the viewpoint of design. After enamel glaze is applied and baked, the pictures and patterns are transferred. For this reason, in addition to the usual enamel firing, firing for transfer is required. However, in such an application, since the steel sheet is subjected to severe processing, coarse grains are generated in the steel sheet by firing the enamel a plurality of times, and the steel sheet is easily softened. The softening of the steel sheet reduces the strength of the enamel product, and the enamel layer is easily broken by deformation. Further, if the steel sheet is softened, it is not preferable because the steel sheet is easily deformed when fired again.

[0004] Since enamels generally tend to decrease in adhesion as the number of firings increases, a steel sheet having excellent adhesion is desirable for the above applications. Further, in consideration of workability, an extremely low carbon steel sheet is preferable. Although the above high oxygen steel reduces C and N as much as possible in the steelmaking stage,
Since solid solution C and N are present in steel, workability and aging resistance are relatively poor, and are insufficient for uses such as pots and kettles.

As a countermeasure for improving aging resistance, addition of Ti or the like to steel is disclosed in, for example,
It is disclosed in JP 7742. However, in this method, the amount of Ti oxide is increased, and nail jump resistance becomes unstable. Further, the present inventors have proposed to add B before to improve aging resistance (Japanese Patent Application No. 8-259).
467). However, when B is added, it is likely to bond with oxygen at the steel making stage, so that it is difficult to cast, slab cracks are easily generated, and the rolling load is increased. Therefore, an element that replaces B and improves aging resistance is desired. On the other hand, there is no example of examining the softening characteristics of the steel sheet by firing.

[0006]

As described above, a cold-rolled steel sheet for enamel which has excellent workability and is hard to be softened during enamel firing has not yet been obtained. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a cold-rolled steel sheet for enamel which is excellent in workability and hardly softens during enamel firing while maintaining good enamel properties. Aim.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, in order to obtain a steel sheet which is excellent in workability and hard to soften during enamel firing, It has been found that the addition of Cr and Nb is effective. That is, Cr has an effect of improving workability, particularly deep drawability by combining with Mn and O in steel, and Nb has a plastic strain ratio (r) through refinement of ferrite grains of a hot-rolled sheet.
Value), the anisotropy (Δr) of the plastic strain ratio, and the effect of bonding with C and N in steel to improve aging resistance and prevent softening during enamel firing.

[0008] The present invention has been made based on such findings, and in terms of% by weight, C: 0.005% or less;
i: 0 to 0.05%, Mn: 0.2 to 0.7%, P:
0.004 to 0.025%, S: 0 to 0.025%, s
ol. Al: 0 to 0.01%, O: 0.045 to 0.1
%, Cu: 0.02-0.05%, N: 0.005% or less, Nb: 0.01-0.1%, and 0.5O-
An object of the present invention is to provide a cold-rolled steel sheet for enamel which is excellent in workability and which is hardly softened during enamel firing, characterized by containing 2.5O of Cr. In addition, 0.1% by weight%.
An object of the present invention is to provide a cold-rolled steel sheet for enamel which has excellent workability and is hard to be softened during enamel firing, characterized by containing 001 to 0.1% of V.

The present invention also provides C: 0.005% by weight.
%, Si: 0 to 0.05%, Mn: 0.2 to 0.7
%, P: 0.004 to 0.025%, S: 0 to 0.02
5%, sol. Al: 0 to 0.01%, O: 0.045
0.1%, Cu: 0.02 to 0.05%, N: 0.0
0.05% or less, Nb: 0.01 to 0.1%, and 0.
After hot rolling is performed on steel containing 5O to 2.5O Cr, it is rolled at a temperature of 640 ° C or higher to obtain a hot-rolled steel sheet, and after pickling and cold rolling, 800 ° C or higher and 850 ° C. An object of the present invention is to provide a method for producing a cold-rolled steel for enameling, which is characterized by performing continuous annealing at the following temperature, which is excellent in workability and is not easily softened during enameling. Also, the weight%
The present invention provides a method for producing a cold-rolled steel sheet for enameling, characterized by containing 0.001 to 0.1% of V, excellent in workability, and hard to soften during enamel firing.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail by dividing into components and compositions of steel and manufacturing methods. 1. Steel composition The steel composition and composition of the steel sheet of the present invention is as follows: C: 0.00
5% or less, Si: 0 to 0.05%, Mn: 0.2 to 0.
7%, P: 0.004 to 0.025%, S: 0 to 0.0
25%, sol. Al: 0 to 0.01%, O: 0.04
5 to 0.1%, Cu: 0.02 to 0.05%, N: 0.
005% or less, Nb: 0.01 to 0.1%, Cr: and 0.5O to 2.5O, and V: 0.0 as a selective component
It may contain from 0.1 to 0.1%.

C, N: If the amounts of C and N are too large, the aging resistance deteriorates. Therefore, it is desirable that C and N are as small as possible. Therefore, the content of each of C and N is set to 0.0
It shall be not more than 05%. These preferred ranges are 0.00
25% or less.

Si: When smelting steel, Si is added as necessary to adjust the amount of oxygen in the steel. However, a smaller amount is better for improving the surface properties of steel. That is, if it exceeds 0.05%, surface defects related to the Si scale are likely to occur. Therefore, the content of Si is set to 0.1.
Not more than 05% (including the case of no addition).

Sol. Al: Al is added as necessary to control the amount of oxygen in the steel when melting the steel. However, if the amount of Al added is too large, sol. Al combines with N in steel to form fine AlN, which significantly deteriorates workability of steel. Therefore, Al should not be added as much as possible, and sol. The content of Al is set to 0.01% or less (including no addition). A preferred range is 0.002% or less.

Mn: Mn combines with O in steel to form MnO.
By acting as a trap site for H that has entered during the enamel firing, the nail jump resistance is improved. Also, M
A part of n forms a composite oxide with Cr, which forms a texture preferred for deep drawability. However, when the amount of Mn is 0.2
%, There is no effect, and if it exceeds 0.7%, the workability of steel is deteriorated. Therefore, the content of Mn is 0.2 to
0.7%. However, as in the present invention, the amount of O is large,
In a system to which Nb is added, since Nb does not become an oxide, it is preferable that the Mn content be large,
% Is preferred.

Cr: Cr not only improves workability but also contributes to improvement in nail jump resistance. Cr is Nb
Since it is more easily oxidized, Nb added in the present invention hardly turns into an oxide, and the addition of Cr makes r
The effect of improving the value, the effect of improving the anisotropy of the r value, and the effects of improving the aging resistance and the softening property upon firing can be sufficiently exhibited. Cr forms a composite oxide with Mn and O, reduces fine oxides that hinder the movement of crystal grain boundaries, and contributes to the improvement of deep drawability by improving the growth of ferrite grains during annealing. Can be Therefore, Cr becomes O
It is necessary to specify the amount according to the amount of Cr is O
If the value is less than 0.5, the above effect cannot be sufficiently exerted. If the value exceeds 2.5, the amount of solid-solution Cr increases and the workability deteriorates. Therefore, the content of Cr is set to 0.5O-2.
The range is 5O. The preferable range of the amount of Cr is 0.8O to
1.5O.

O: O combines with Mn, Cr and Fe in steel to form an oxide and contributes to nail jump resistance as an H trap site. In addition, Cr and Mn partially form an oxide to form a texture that contributes to improvement in workability, particularly in deep drawability. However, if the O content is less than 0.045%, the effect is not obtained. If the O content is more than 0.1%, Nb easily forms an oxide, and the effect of Nb is reduced. Therefore, the content of O is set in the range of 0.045 to 0.1%. However, the content is preferably 0.05% or more from the viewpoint of nail skip resistance and 0.07% or less from the viewpoint of workability.

When Cr is added as in the steel sheet of the present invention,
Since the pickling weight loss value increases, P, S, C
It is necessary to adjust the amount of u to secure adhesion and foamability.

P: P greatly affects the pickling weight loss value and affects the adhesion of the enamel. That is, when the P amount is 0.
If it is less than 004%, the pickling rate is too slow and a sufficient pickling weight loss value cannot be obtained under normal pickling conditions. On the other hand, 0.025%
If it exceeds 300, the pickling weight loss value becomes too large, and foam defects are likely to occur, for example, when the dew point during firing is high. From this viewpoint, the content of P is set in the range of 0.004 to 0.025%. However, in order to ensure extremely good foam resistance, the content is preferably 0.015% or less.

S: S has the effect of increasing the pickling weight loss value and affects the enamel adhesion. Also, since it has an effect on nail skip resistance, it is added as necessary. However, in the system to which Nb is added as in the present invention, particularly when the amount of S is too large, the workability and the adhesion tend to deteriorate. For this reason,
The S content is set to 0.025% or less. More preferably,
It is in the range of 0.015 to 0.02%.

Cu: Cu is an element that increases the unevenness of the interface between the enamel layer and the steel sheet during enamel firing and improves the enamel adhesion. However, if the Cu content is less than 0.02%, good adhesion cannot be obtained under ordinary enamel conditions. On the other hand, Cu is an element that reduces the pickling rate during the enamel pretreatment, and if added in excess of 0.05%, the pickling weight loss value becomes too small, and good adhesion can be obtained under ordinary enamel conditions. Can not. Therefore, the Cu content is in the range of 0.02 to 0.05%. However, in order to obtain extremely good adhesion, 0.025 to 0.025
A range of 35% is more preferred.

Nb: Nb improves the r-value and the anisotropy of the r-value by reducing the grain size of the hot-rolled sheet, and increases the C content in the steel.
And N contribute to the improvement of the aging property of steel. Further, Nb precipitates and solid solution Nb at the time of firing the enamel have an effect of preventing ferrite grains from coarsening. The effect of improving the r value by adding Nb doubles the effect of improving the deep drawability of the composite oxide of Cr and Mn. However, the Nb content is 0.01%
If it is less than Nb, Nb almost becomes an oxide, and the above effect cannot be obtained.
A large amount of system oxides are generated, and nail jumping is likely to occur. Therefore, the Nb content is in the range of 0.01 to 0.1%. A preferred range is from 0.02 to 0.06%.

V: V combines with N or C in steel,
It is an optional component that is added as necessary to contribute to the improvement of aging resistance of steel. However, if the V content is less than 0.001%, most of the oxide will be an oxide, and there is no effect. If it exceeds 0.1%, the workability and enamelness of the steel will deteriorate. Therefore, when V is added, its content is set in the range of 0.001 to 0.1%. A preferable range is 0.02 to 0.04%.

For the other elements, Ni is 0.05
%, Sn is 0.01%, As is 0.01%, and Sb is 0.1%.
Even if it is contained up to 01%, the effect of the present invention is not impaired. In the present invention, B is not intentionally added.

2. Manufacturing Method First, a slab whose components are adjusted within the above-described steel component range is manufactured. Regarding slab production, in the steel ingot method, coarse inclusions are likely to exist between the rim layer and the core portion, and blister defects are likely to occur after enamel processing. Therefore, it is preferable to manufacture by a continuous casting method.

After casting, the steel slab is cooled and then heated to perform hot rolling, or after casting, the steel slab is directly subjected to hot rolling without heating. The hot rolling conditions are not particularly limited, and may be performed according to a conventional method. However, in the steel to which Nb is added as in the present invention, the heating temperature is preferably 1150 ° C. or lower in order to suppress the solid solution of Nb precipitates due to heating. At the time of hot rolling, the effect of the present invention is not impaired even if the steel sheet after rough rolling is heated again to a heating temperature or lower. The finish rolling is preferably performed at a temperature from the Ar ₃ transformation point to 900 ° C. or less. Thereby, ferrite grains of the hot-rolled sheet are refined, and workability of steel is improved. On the other hand, the finishing temperature is 900 ° C
By the following, since the austenite grains before finish rolling are reduced, the grain growth of ferrite grains is suppressed,
Workability is improved.

In the present invention, winding after finish rolling is performed by N
The temperature is preferably set to 640 ° C. or higher in order to precipitate precipitates such as bC coarsely and to reduce decomposition during annealing. On the other hand, if the winding temperature is too high, the pickling property deteriorates. In the present invention, the effect of the present invention is not impaired even when the rough rolling is omitted and the finish slab is directly applied to the thin slab.

After the hot rolling, the steel strip is pickled and then cold rolled. The cold rolling conditions are not particularly limited, and may be performed according to a conventional method. However, the cold rolling rate is preferably set to 70% or more from the viewpoint of workability.

After the cold rolling, the steel strip is annealed. The method for producing the steel strip is not particularly limited, and any of a box annealing method (tight coil annealing method), an open coil annealing method, and a continuous annealing method may be used. However, the continuous annealing method is preferred from the viewpoint of cost and production time. The annealing temperature in continuous annealing is preferably 800 ° C. or less from the viewpoint of workability. However, if the annealing temperature is too high, NbC is melted and the aging resistance is deteriorated. The annealed steel strip can be used as a product as it is, but may be subjected to temper rolling at an elongation of 5.0% or less, if necessary, in order to improve the nail skipping property and secure the shape. However, from the viewpoint of preventing softening during baking of the enamel, the lower the elongation, the better.
0% or less is more preferable.

[0029]

【Example】

(Example 1) Steel having the components shown in Table 1 was formed into a slab by a continuous casting method. After heating at 1120 ° C, finishing temperature is 890 ° C
Was hot-rolled to a thickness of 2.8 mm and wound at 680 ° C. on a coil. After pickling the obtained hot-rolled steel strip, 0.7
mm (rolling rate = 75%). The obtained cold-rolled coil was continuously annealed at a heating rate of 7 ° C./second at 820 ° C. for 30 seconds, and subjected to a 1.0% temper rolling to obtain a cold-rolled steel sheet for enamel. A JIS No. 5 test piece was sampled from the steel sheet in the rolling direction and subjected to a tensile test. Further, JIS No. 5 test pieces were sampled from the rolling direction, the rolling direction at 45 degrees and the direction perpendicular to the rolling direction, and the Rankford value (mean r value) was measured. Average r value = (r value in rolling direction + 2 × r value in rolling direction and 45 ° + r value in direction perpendicular to rolling) / 4 Further, in order to evaluate mechanical properties after firing, 850 ° C. ×
The mechanical properties after firing for three minutes in three minutes were evaluated using JIS No. 5 test pieces.

Further, the enamel characteristics were examined under the following conditions. However, in the adhesion test, baking was performed three times to simulate the lower glaze, the upper glaze, and the transfer under a condition of short sulfuric acid pickling time in which good adhesion was difficult to obtain. In the nail skipping resistance test, a glaze that easily causes nail jumping was used, and the test was performed without acid pickling and under a condition in which the dew point (DP) during firing was high (accelerated test).

Adhesion test Pretreatment: alkaline degreasing → sulfuric acid washing (15% H ₂ SO ₄ , 7
0 ° C × 3min) Glaze: H glaze made by Nippon Ferro, target-100μ each on both sides
m Firing: 850 ° C. × 2 min, firing was performed three times. The adhesion was measured by a PEI method for ten samples (100 × 100 mm).

Nail skipping resistance test Pretreatment: alkali degreasing only (sulfuric acid washing, no Ni-dip) Glaze: Nippon Ferro H: 1553B = 1: 1 mixed glaze, target-100 μm on both sides Firing: 830 ° C. × 2min (humidified atmosphere, DP = 30
C.) This was enameled on 10 samples (100 × 100 mm), and the nail jump was generated when at least one of the nails had formed on both sides.

Table 2 shows the results. From Table 2, it was confirmed that the steel sheet of the present invention has both workability and enamelness. Further, it was confirmed that hardening hardly occurred after firing three times. Further, it was confirmed that within the scope of the present invention, the steel to which V was added as a selective component had further improved aging resistance. The reason why YS after firing three times is larger than YS of the annealed plate is to recover the yield point elongation.

On the other hand, since the steel sheet 21 has too much C content, the workability and the aging resistance are inferior. Since the steel sheet 22 has too much P content, the workability and the adhesion are deteriorated. Since the steel sheet 23 has too much S content, the workability and the adhesion are inferior. Since the steel sheet 24 has too much N content, workability and aging resistance are inferior. The steel plate 25 has an excessively small amount of oxygen, so that a nail jump occurs. Since the steel sheet 26 has too much Cu, the adhesion is inferior. Since the steel sheet 27 has too little Cr, the deep drawability is not very good. Further, since Cr is small, most of the added Nb becomes an oxide, and the effect of improving the deep drawability, the effect of improving the anisotropy, the effect of improving the aging resistance, and the effect of preventing sintering softening by adding Nb are hardly recognized. Since the steel sheet 28 does not contain Nb, the deep drawability, anisotropy, aging resistance, and firing softening properties are inferior. Since the steel plate 29 has an excessively large amount of Nb, the nail skip resistance is inferior. Since the steel plate 30 has too much V, the workability is deteriorated. Since the steel plate 31 contains Ti, the nail skip resistance is deteriorated.

[0035]

[Table 1]

[0036]

[Table 2]

(Example 2) In order to clarify the influence of Nb on workability, Nb was added to steel having the components and compositions shown in Table 3 to produce a slab by continuous casting. 1130
After heating at ℃, hot rolling was performed at a finishing temperature of 890 ° C to a thickness of 2.8 mm, and the coil was wound at 660 ° C. After pickling the obtained hot-rolled steel strip, it was cold-rolled to 0.7 mm (rolling ratio = 75%). The obtained cold-rolled coil was heated at a heating rate of 7
Continuous annealing at 850 ° C. for 30 seconds at a rate of 1.0 ° C./sec.
% Cold-rolled steel sheet for enamel. The YS after firing at 850 ° C. × 3 minutes × 3 times was measured from the obtained steel sheet in the same manner as in Example 1, and a nail skipping resistance test was further performed. The results are shown in FIG. FIG. 1 is a diagram showing the relationship between the Nb amount on the horizontal axis and the YS and nail jump occurrence rates on the vertical axis. From this figure, it can be seen that YS after firing three times is high and Nb is not generated within the range of the present invention within the range of the present invention.

[0038]

[Table 3]

(Example 3) Steel having the components shown in Table 4 was melted and continuously cast into a slab, and then directly rolled or heated at 1100 ° C and hot-rolled to 3.2 mm to obtain a slab.
Finish rolling was performed at 80 ° C., and the film was wound around a coil at a temperature shown in Table 4. After the obtained hot-rolled steel strip was pickled, the sheet thickness was reduced to 0.1 mm.
It was cold rolled to 8 mm (75% cold pressure). The obtained cold-rolled coil was annealed at the temperature shown in Table 4 and subjected to a temper rolling of 0.8% to obtain a product. A JIS No. 5 test piece was collected from the product, and the average r value was measured. Table 4 shows the obtained results. It can be seen that a high average r value is obtained at the winding temperature and annealing temperature within the range of the present invention, and that the aging resistance is good.

[0040]

[Table 4]

[0041]

As described above, according to the present invention,
A cold-rolled steel sheet for enamel having excellent workability and sintering softening properties while maintaining good enamel properties is obtained, and its industrial value is extremely high.

[Brief description of the drawings]

FIG. 1 is a view showing the relationship between the Nb amount, YS, and the occurrence rate of nail jump.

Claims (4)

[Claims] C. 0.001% or less by weight of C
i: 0 to 0.05%, Mn: 0.2 to 0.7%, P:
0.004 to 0.025%, S: 0 to 0.025%, s
ol. Al: 0 to 0.01%, O: 0.045 to 0.1
%, Cu: 0.02-0.05%, N: 0.005% or less, Nb: 0.01-0.1%, and 0.5O-
A cold-rolled steel sheet for enamel which has excellent workability and is hard to be softened during enamel firing, characterized by containing 2.5O of Cr. 2. Further, 0.001 to 0.1% by weight.
The cold-rolled steel sheet for enamel according to claim 1, which is excellent in workability and hardly softens during enamel firing. 3. C: 0.005% or less in weight%, S
i: 0 to 0.05%, Mn: 0.2 to 0.7%, P:
0.004 to 0.025%, S: 0 to 0.025%, s
ol. Al: 0 to 0.01%, O: 0.045 to 0.1
%, Cu: 0.02-0.05%, N: 0.005% or less, Nb: 0.01-0.1%, and 0.5O-
After hot rolling is performed on steel containing 2.5O Cr, the steel is rolled at a temperature of 640 ° C or higher to obtain a hot-rolled steel sheet, and after pickling and cold rolling, 800 ° C or higher and 850 ° C or lower. A method for producing cold-rolled steel for enamel which has excellent workability and is hardly softened during enamel firing, characterized by performing continuous annealing at a temperature. 4. Further, 0.001 to 0.1% by weight.
4. The method for producing a cold-rolled steel for enamel according to claim 3, which is excellent in workability and hardly softens during enamel firing.