JPH10140286A - Steel sheet for porcelain enameling, excellent in adhesion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a steel sheet for porcelain enameling, excellent in adhesion, and particularly a steel sheet for porcelain enameling, excellent in adhesion even in the case of a low pickling loss value and capable of direct single porcelain enameling, by further increasing C content and regulating respective contents of S, Zr, N, P, Cu, etc., to values in respectively specified ranges. SOLUTION: This steel sheet for porcelain enameling has a composition consisting of, by weight, 0.003-0.005% C, 0-0.05% Si, <=0.4% Mn, 0.005-0.02% P, 0.005-0.02% S, 0.02-0.05% Cu, 0.05-0.2% Zr, 0-0.1% sol.Al, 0.005-0.015% N, <=0.005% O, and the balance Fe and containing 0.0001-0.001% B if necessary. This steel sheet for porcelain enameling is prepared by increasing the contents of C and S, both having a function of accelerating pickling at the time of pretreatment, in a Zr-added steel sheet and preventing the resultant defect of liability to occurrence of blister and black speck defects by controlling the amounts of Cu and P to values in proper ranges, respectively, and excellent adhesion can be obtained even in the case of low pickling loss value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an enameled steel sheet having excellent adhesion, and more particularly to an enameled steel sheet which can be directly enameled and has excellent adhesion even at a low pickling loss value.

[0002]

2. Description of the Related Art Enamel products are widely used in applications such as kitchen utensils, wash basins, building materials and gas ranges.

[0003] In recent years, enamel manufacturers have taken direct measures to streamline the process and improve the thermal shock resistance of enamel products.
Oriented once.

[0004] Since it is difficult to obtain good adhesiveness by directly enameling once, it is necessary to carry out a Ni immersion treatment following the sulfuric acid washing as a pretreatment for the enamel.

[0005] However, if the pickling weight loss value and the Ni adhesion amount are large, enamel defects such as bubbles and black spots are likely to occur.
In addition, a large pickling loss value causes an increase in the cost of treating the waste liquid in pickling.

[0006] For these reasons, there is a demand for a steel sheet which is excellent in adhesion even at a low acid wash weight loss and is suitable for direct once-enamelling.

Generally, strict workability is required for enameled steel sheets used for bathtubs, pans, and the like. For applications requiring such strict workability, conventionally, Ti-added steel and B-added steel have been used.

[0008] Further, as the steel for direct enamelling, a steel produced by continuous casting without reducing the amount of carbon in the steel making stage (hereinafter referred to as high oxygen steel) is widely used.

[0009]

However, Ti-added steel and B
Although steel sheets using added steel, etc. are excellent in workability, the enamel conditions are narrow when trying to manufacture enamel products directly in one application, that is, the pickling weight loss value is small, the adhesion is poor, and the pickling is poor. When the weight loss value is large, there is a disadvantage that enamel defects such as bubbles and black spots are easily generated. For this reason, it is difficult to use the enamel directly once and it is difficult to use it stably.

[0010] In the case of high oxygen steel, unless the pickling weight loss value is increased, excellent enamelability cannot be obtained directly after one application. Further, since solid solution C and N exist in steel, workability and aging resistance are insufficient, and use in applications requiring strict workability is limited.

That is, at the present time, a steel sheet suitable for direct single-use enamel which has excellent adhesion even with a small pickling weight loss value has not been developed.

The present invention has been made in view of such circumstances, and has a good adhesive property, particularly an enameled steel sheet that can be directly enameled and has a good adhesion even at a low acid wash weight loss value. The purpose is to provide.

[0013]

Means for Solving the Problems The present inventors have studied a steel sheet which is excellent in workability and enamelability, in particular, even once directly, and found that Zr-added steel is effective. Patent application for a steel sheet with excellent workability and enamelness to which 0.05 to 0.2 wt% of Zr is added (Japanese Patent Application No. Hei.
280264). However, the steel sheet was not always satisfactory in adhesion at a low acid wash weight loss value.

[0014] Therefore, further studies were conducted on the adhesion of a steel sheet containing Zr at a low acid wash weight loss value.

As a result, the surface of the steel sheet is finely divided at the time of sulfuric acid pickling in the enamel pretreatment, and the pickling is performed following the pickling.
When Ni is uniformly and finely precipitated on the surface of the steel sheet during the Ni immersion treatment, excellent adhesion can be obtained even with a low pickling weight loss value. The state of precipitation and the precipitation state of Ni at the time of Ni immersion treatment change, and as precipitates, the influence of carbides and sulfides is large, especially carbides and sulfides of Zr, finely roughen the steel sheet surface during pickling,
It has been found that the effect of uniformly and finely depositing Ni on the steel sheet surface during the Ni immersion treatment performed after the pickling is excellent.

[0016] In view of the above, a study was made of a steel component composition which is excellent in adhesion and can be directly enameled even at a low acid wash weight loss value. As a result, the C content of the steel sheet was further increased, and S, Zr, It was found that by limiting the composition of components such as N, P, and Cu to a specific range, it is possible to obtain a steel sheet which has excellent adhesion and can be directly enameled once even at a low acid wash weight loss value.

Further, when the contents of C and S are increased as in the present invention, bubbles and black spot defects are liable to occur, and the adhesion at a low pickling loss value is improved while preventing these defects. It has been found that it is important to control the amounts of Cu and P within an appropriate range in order to achieve the above.

The reason why the above-mentioned effects are brought about by the carbides and sulfides is that the carbides and sulfides are left undissolved during the pickling with sulfuric acid, and in addition to promoting the dissolution of iron and roughening of the steel sheet surface. This is considered to be due to the role of the cathode during the Ni immersion treatment, whereby Ni can be uniformly and finely deposited.

The reason why the effect of carbides and sulfides of Zr is particularly large is that Zr has a large bonding force with C and S, so that the carbides and sulfides of Zr easily precipitate in a hot-rolled sheet.
The precipitate once deposited is less likely to be decomposed during annealing, so that the above-mentioned effects are reliably obtained, whereas Ti, N
b, Carbides and sulfides such as REM and V have a smaller bonding force than carbides and sulfides of Zr, so they are less likely to precipitate in hot-rolled sheets, and partly decompose during annealing of steel sheets. It is considered that the above-mentioned effects are hardly obtained.

The present invention is based on this finding,
The characteristic configuration is as follows. (1) wt%, C: 0.003-0.005%, Si: 0-0.05%, Mn ≦
0.4%, P: 0.005 to 0.02%, S: 0.005 to 0.02%, Cu: 0.02
~ 0.05%, Zr: 0.05 ~ 0.2%, sol.Al:0~0.1%, N: 0.005
An enameled steel sheet having excellent adhesion, which satisfies 0.00.015%, O 2 ≦ 0.005%, and the balance substantially consists of Fe. (2) In the steel sheet according to (1), in wt%, B: 0.0001 to 0.001%
An enameled steel sheet with excellent adhesion, characterized by the addition of.

Hereinafter, the reasons for limiting the composition of each component of the present invention will be described. C: 0.003 to 0.005% S: 0.005 to 0.02% C, S has the function of accelerating pickling during the pretreatment of enamel and promotes roughening of the steel sheet surface after pickling. It is effective for improving the adhesion. Also, after pickling, the steel sheet surface is concentrated as a smut, and Ni
Promotes fine and uniform precipitation of Ni on the steel sheet surface during the immersion treatment. In order to exhibit this effect, C is added at 0.003% or more and S is added at 0.005% or more. However, if these contents are too large, even at a low acid wash weight loss value, C and S react with moisture at the time of firing the enamel, causing bubbles and black spot defects, so C is 0.005% or less, S is 0.02% The following is assumed.

Si: 0 to 0.05% Si is added as necessary to deoxidize the steel and secure Zr necessary for the formation of Zr precipitates in the steel, which is the main feature of the present invention. It may be 0 (no addition). However, if the amount of Si is too large, surface defects of the steel sheet are likely to occur, so the upper limit is made 0.05%.

Sol.Al: 0-0.1% Al is added as necessary to deoxidize the steel and to secure Zr necessary for the formation of Zr precipitate in the steel, which is the main feature of the present invention. It may be 0 (no addition). However, if there is much sol.Al, Al
Is combined with N to degrade nail skip resistance, so the content is 0.1% or less, preferably 0.05% or less.

Mn ≦ 0.4% Mn combines with S and has the effect of suppressing hot cracking. However, if the addition amount is too large, the amount of sulfide of Zr decreases, and the effect of improving the adhesion at a low acid wash weight loss value by the sulfide is suppressed, so that the content is 0.4% or less, preferably 0.35% or less. I do.

P: 0.005% to 0.02% Cu: 0.02% to 0.05% P and Cu are elements that improve the adhesiveness. In order to obtain good adhesiveness by directly applying once with a low pickling weight loss value, P
, Cu content is important. P is 0.005% to improve adhesion
As described above, Cu needs to be added in an amount of 0.02% or more. But P
If the amount is too large, the foam resistance and the black spot property deteriorate, and if the P and Cu amounts are too large, the above-mentioned effects due to carbides and sulfides are negated, so that the P amount is 0.02% or less and the Cu amount is 0.05% or less. I do.

Zr: 0.05-0.2% Zr forms carbides, nitrides and sulfides. Zr carbides and sulfides make the steel sheet surface fine during sulfuric acid pickling in the enamel pretreatment, and uniformly and finely precipitate Ni during Ni immersion treatment to improve adhesion at low pickling weight loss value . In addition, nitride serves as a trap site for hydrogen, and is effective in improving nail jump resistance. To achieve these effects, Zr
Is required to be 0.05% or more, preferably 0.08% or more. However, if the amount of Zr is too large, the amount of Zr dissolved in steel increases,
The Zr content is set to 0.2% or less, because the pickling speed becomes slow and it is difficult to make fine roughening of the steel sheet surface after the pickling.

O ≦ 0.005% O is an element inevitably contained in steel. In steel
As the amount of O 2 increases, the amount of oxides, particularly the oxides of Zr, increases. This is substantially equivalent to a decrease in the amount of Zr, and it is difficult to obtain the above-described effects. Further, oxides near the surface layer of the steel sheet increase, and the surface defects of the steel sheet increase. In addition, if there is a coarse oxide, hydrogen is absorbed during firing of the enamel, and blister defects are likely to occur. For these reasons, O is set to 0.005% or less.

N: 0.005% to 0.015% N forms a nitride with Zr, serves as a hydrogen trap site, and is effective in obtaining excellent nail jump resistance. To obtain this effect, the N content must be at least 0.005%, preferably at least 0.007%. However, if it exceeds 0.015%, AlN precipitates,
Since not only bubbles and black spot defects are likely to be generated but also most of Zr is bonded to N and it is difficult to obtain the above-mentioned effects of carbides and sulfides, the upper limit is made 0.015%.

B: 0.0001 to 0.001% B is added as necessary to improve the resistance to secondary working brittleness. 0.0001% to improve secondary work brittleness
The above addition is necessary. However, if the amount is too large, B forms a nitride, and the nitride reacts with moisture during the enamel firing, causing bubbles and black spot defects.
1% or less is good.

REM, Nb, Ti, and V are not added, but when they are mixed as unavoidable impurities, REM, Nb, Ti, and V are added in an amount of 0.005%.
Control to less than%. Further, it is possible to add a trace amount of any other element within the range not impairing the effect of the present invention.For example, for Ni, Cr, Co, Mo, W, addition of 0.05% or less, Sn, As , The addition of 0.01% or less is permitted.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a steel sheet according to the present invention will be described.

A steel slab adjusted to the composition range according to claim 1 or 2 is manufactured. The slab is preferably produced by continuous casting from the viewpoint of cost and uniformity of components. Also, the method of adding Zr only to the slab core is not preferable because C and N in the surface layer of the slab do not bond with Zr, and the aging resistance is deteriorated. The slab manufactured by continuous casting is 1 to 7 mm as necessary to prevent surface defects on the steel sheet.
Slab surface grinding.

The slab thus manufactured is directly hot-rolled or directly re-heated, and then hot-rolled. The reheating temperature is preferably 1200 ° C. or lower in order to coarsen precipitates and improve workability. Hot rolling is
In order to ensure workability, it is preferable that the finishing temperature be equal to or higher than the Ar ₃ transformation point. The winding temperature is 60 from the viewpoint of workability.
0 ° C or higher is good. However, if the winding temperature is too high, the formed scale becomes thick, the descaling property (pickling property) is inferior, and the yield is reduced.

Next, after descaling, cold rolling, annealing,
The steel sheet of the present invention is obtained by adjusting the pressure. The cold rolling ratio of the cold rolling is preferably 50% or more from the viewpoint of workability. However, if the cold pressure ratio is too high, the deep drawability and anisotropy deteriorate, so the cold pressure ratio is preferably 95% or less.

The annealing may be either a box annealing method or a continuous annealing method. From the viewpoint of workability, the annealing temperature is equal to or higher than the recrystallization temperature.
Ac ₃ points or less is good.

The pressure regulation rate of the pressure regulation is preferably 0.3% or more in order to improve the aging resistance and the nail skip resistance by forming microvoids.

To obtain the steel of the present invention, the steel may be refined in an electric furnace, or rough rolling may be omitted in hot rolling and finish rolling may be performed.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. (Example 1) A slab was produced by melting a steel having the composition shown in Table 1 and the balance consisting of Fe and unavoidable impurities. Thereafter, hot rolling was performed at a slab heating temperature of 1180 ° C. and a finishing temperature of 890 ° C. to form a hot-rolled sheet having a thickness of 2.8 mm, which was wound at 620 ° C. Next, after pickling, cold rolling was performed to a sheet thickness of 0.8 mm (cold pressure ratio: 71%), followed by continuous annealing at a soaking temperature of 850 ° C for 60 seconds, and pressure regulation at a pressure regulation ratio of 0.6%. Thus, a cold-rolled steel sheet was obtained.

[0039]

[Table 1]

The workability, adhesion and enamelness of the cold-rolled steel sheet obtained above were evaluated. The workability was evaluated by a tensile test and a secondary work brittleness resistance. The tensile test was evaluated by a tensile test value using a JIS No. 5 tensile test piece. The resistance to secondary working brittleness was determined by forming a test material into a cup with a drawing ratio of 2.1, pressing a conical punch into the cup, and evaluating the adhesion at a temperature at which vertical cracking did not occur (vertical cracking transition temperature). × 10
Ten test pieces of 0 mm were pickled at a low pickling weight loss value under the following conditions, and immersed in Ni, and then directly enameled once, and the adhesion of the test materials after firing the enamel was measured by the PEI method. .

Pretreatment: degreasing → pickling with sulfuric acid (15% H ₂ SO ₄ , the pickling time was adjusted so that the pickling loss value at 70 ° C. was 15 to 20 g / m ² ) → Ni immersion (NiSO _{4 · 7H 2 O: 13g / l} , pH: 2.6,70 Ni deposition amount was adjusted to be 0.5 to 1.0 g / m ² at ° C.) → neutralization glazed: Japanese Fuero 1553C glaze target thickness: 100 to both sides μm increments Firing: 830 ° C × 3 minutes For enamel, directly under the conditions described below
The foam enamel was evaluated for foam resistance, black spot resistance and nail jump resistance.

For foam resistance and black spot resistance, the size was 100 × 10
Ten test pieces of 0 mm were pickled and immersed in Ni under the following conditions, then enamelled, and the appearance of the test pieces after firing the enamel was visually observed to check for the occurrence of bubbles and black spot defects.
As a result of the investigation, the ratio of the number of test materials in which bubbles and black spot defects were generated to ten test materials was determined, and the result was defined as a bubble generation rate (%).

In order to easily generate bubbles and black spot defects,
The treatment was performed by increasing the pH of the Ni immersion treatment liquid to increase the amount of Ni attached, and increasing the dew point during firing.

Pretreatment: degreasing → pickling with sulfuric acid (15% H ₂ SO ₄ , the pickling time was adjusted so that the pickling loss value at 70 ° C. was 15 to 20 g / m ² ) → Ni immersion (NiSO4 · _{7H 2 O: 13g / l,} pH: 3.1,70 ℃ were adjusted to Ni deposition amount is 2.0 to 2.5 g / m ² in) → neutralization glazed: Japanese Fuero 1553C glaze target thickness: 100 on both sides μm Firing: 830 ° C x 3 minutes, humidified atmosphere (dew point: 30 ° C) For nail flap resistance, pickle 10 pieces of 100 x 100 mm size under the following conditions, pickle them, immerse them in Ni, and enamel them. And visually observe the appearance of the test material after firing the enamel,
The occurrence of nail jump defects was investigated. As a result of the investigation, the ratio of the number of the test materials having the nail jump defect to the ten test materials was determined, and the result was defined as the nail jump occurrence rate (%).

It should be noted that a nail jump defect is likely to occur,
The pickling time and the Ni immersion treatment time were shortened, and the dew point during firing was increased.

Pretreatment: degreasing → sulfuric acid pickling (15% H ₂ SO ₄ , 70 ° C. × 2 minutes) → Ni immersion (NiSO ₄・ 7H ₂ O: 13 g / l, pH 2.6, 70 ° C. × 2 minutes) → Neutralization Glaze: Japan Fellow 1553C glaze Target thickness: 100 μm on both sides Firing: 830 ° C x 2 minutes, humidified atmosphere (dew point: 30 ° C) Table 2 shows the survey results.

[0047]

[Table 2]

Tables 1 and 2 show the following. The steel sheet of the present invention having a steel component composition within the range of the present invention has good adhesion, and does not show any occurrence of bubbles, black spot defects, and nail jump defects.

Further, B satisfying the second aspect of the present invention.
The steels 34 and 35 added with have improved secondary work brittleness resistance.

On the other hand, the comparative steel sheet having a steel component composition outside the range of the present invention is inferior in at least one of adhesion or enamelness (foam resistance / black spot resistance or nail jump resistance).

That is, the steel 19 having a small C content has insufficient adhesion. Steel 20 having too much C content has poor foam resistance and black spot resistance.

The steel 21 having a small P content and the steel 23 having a small S content are:
Poor adhesion. Steel 24 with a high S content has poor foam resistance and black spot resistance. Steel 22 having a large amount of P is inferior in adhesion, bubble resistance and black spot resistance.

The steel 25 having a large amount of Cu has poor adhesion. Steel 26 with a small amount of N has poor nail jump resistance. Steel 27 with a large amount of N
Poor adhesion, foam resistance and black spots.

Steel 28 with a large amount of Zr has poor adhesion. Steel 29 with a high O content has poor adhesion.

Further, the steel 30 containing REM, the steel 31 containing Nb, the steel 32 containing Ti, and the steel 33 containing V in excess of 0.005% each have inferior foam resistance and black spot resistance.

Steel 36 having a B content exceeding the range of the second invention of the present invention is inferior in foam resistance and black spot resistance. Incidentally, the steel sheet of the present invention, Zr
Is not added only to the core, and the steel sheet of the present invention is manufactured by continuous annealing that can achieve uniform heat treatment conditions in the longitudinal direction and width direction of the steel sheet, so that the steel sheet of the present invention has a very small variation in the material in the longitudinal direction of the coil, It was uniform.

(Example 2) Next, Si: 0.01 to 0.02%, Mn:
0.2-0.3%, P: 0.012-0.017%, Cu: 0.025-0.034%, So
l.Al: 0.015-0.039%, N: 0.0083-0.0122%, O: 0.0011-
The steel with the C and S contents changed at 0.0024% was melted,
Steel sheets were manufactured under the same conditions as in 1. The obtained steel sheet was enameled under the same conditions as in Example 1, and the adhesion, foam resistance and black spot resistance were examined. However, 90% for adhesion
Less than was regarded as poor adhesion. In addition, a bubble or a black spot defect was evaluated as having a bubble or a black spot. Fig. 1 shows the survey results.

FIG. 1 shows that when the C and S contents satisfy the range of the present invention, the adhesion is excellent at a low acid wash weight loss value, and no bubbles and black spot defects are generated. When the amounts of C and S are below the range of the present invention, the adhesion decreases at a low acid wash weight loss value, and when the amounts of C and S exceed the range of the present invention, bubbles and black spot defects occur.

[0059]

As described above, the steel sheet of the present invention
Excellent adhesion even at low acid wash weight loss. Therefore, it is possible not only to expand the application of direct enamelling, which was previously difficult with a low pickling weight loss value, but also to expand the application where enamelling was not performed due to the limitations of workability. Therefore, a remarkably great effect such as a reduction in energy and a reduction in the cost of treating the waste liquid of pickling is brought about.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the C and S contents of a steel sheet and adhesion, foam resistance and black spot resistance.

Claims (2)

[Claims] (1) In wt%, C: 0.003 to 0.005%, Si: 0 to 0.05
%, Mn ≦ 0.4%, P: 0.005 to 0.02%, S: 0.005 to 0.02%,
Cu: 0.02-0.05%, Zr: 0.05-0.2%, sol.Al: 0-0.1%,
N: 0.005% to 0.015%, O ≦ 0.005%, and the balance is substantially made of Fe. 2. The steel sheet according to claim 1, wherein B: 0.00% by weight.
An enameled steel sheet with excellent adhesion, characterized by adding 01 to 0.001%.