JPH05202420A - Production of cold rolled steel sheet for porcelain enameling - Google Patents

Abstract

PURPOSE:To produce a cold rolled steel sheet for porcelain enameling free from the formation of blister after the firing of porcelain enamel, having superior porcelain enameling characteristics, such as adhesive strength and fishscale resistance, and excellent in formability by specifying a composition and heat treatment conditions, respectively. CONSTITUTION:A continuously cast slab which has a composition consisting of, by weight, <=0.0025% C, <=0.02% Si, 0.05-1.00% Mn, <=0.030% P, 0.005-0.030% S, 0.010-0.100% Al, 0.020-0.100% Ti, 0.010-0.100% Cu, 0.0050-0.0200% N, and the balance Fe with impurities and further satisfying Ti*(%)/C(%)=4 [where Ti*=Ti(Total)-(48/32).S-(48/14)-N] and 2.0-Cu(%)/P(%)<=5.0 is heated at 950-1150 deg.C, hot-rolled, pickled, cold-rolled, and then annealed at a temp. in the region between the recrystallization temp. and the Ar3 transformation point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing cold-rolled steel sheet for enamel having excellent formability, which can be used as a raw material for kitchen ware such as kettles and pots, bathtubs and other difficult-to-form enamel products. ..

[0002]

2. Description of the Related Art Cold rolled steel sheets of rimmed steel that have been decarburized or annealed for decarburization have been widely used as materials for enamel steel sheets. However, since rimmed steel cannot be continuously cast, a slabbing process is required for manufacturing, which not only increases the manufacturing cost, but also makes it a coil.
In the part corresponding to the top part and bottom part of the ingot,
Formability and enamel characteristics may be different from those of the middle portion, and there is also a problem that unevenness is likely to occur.

Therefore, recently, continuous cast steel (CC steel) has come to be used as a material for steel plates for enamel. As continuous cast steel for enamel, oxygen is 200 to 50
Ti is used for high oxygen steel and ultra low carbon Al killed steel that have remained at approximately 0 ppm.
Ti-added steel added with (Japanese Patent Laid-Open No. 55-82748,
56-9357, etc.) etc.

[0004]

Although high oxygen steel has an excellent enamel property similar to that of rimmed steel, it contains solubilized C and solubilized N and is prone to aging deterioration and has poor formability. There is a problem of decrease. In particular, kitchen appliances such as kettles and pots have recently become complicated in shape in order to meet diversifying needs, and materials having high moldability have been demanded. On the other hand, the method of processing enameled steel sheets has shifted from conventional spatula drawing to more efficient press forming, and there has been a demand for enameled steel sheets with good formability. Therefore, the number of cases in which high oxygen steel cannot be applied is increasing.

[0005] Since Ti-added steel fixes C and N by Ti, it has excellent formability and can be used as a raw material for enamel products such as kitchen appliances and bathtubs that are difficult to form.
In many cases, "foam" is generated after enamel firing, and that portion becomes an enamel defect.

In addition to the above-mentioned "foaming", the enameling steel sheet should have the adhesiveness and nail flying resistance ("nail flying": hydrogen in steel). It is necessary to be excellent in the destruction of the enamel.

An object of the present invention is to provide a cold-rolled steel sheet for enamels, which has good enameling performance without generation of "foam" and which can be used as a raw material for enamel products which are difficult to form, and which has excellent formability. It is to provide a manufacturing method of.

[0008]

Means for Solving the Problems As a result of various studies to solve the above problems, the present inventor has estimated that TiC is very likely to be present on the surface of a Ti-added enamel steel sheet where "foam" is likely to occur. It was found that many fine precipitates were present. Enamel firing is performed at a high temperature of 800 ° C or higher in an oxidizing atmosphere. However, if TiC is unstable and easily decomposed, TiC is decomposed in the firing process and the generated C is oxidized.
It becomes CO gas, etc., and it is presumed that this causes "bubbles".

As a factor causing unstable TiC to precipitate, the balance between the heating temperature of the slab and the contents of C, N and S relative to the Ti content is important. If the heating temperature of the slab is too high, coke will be generated during heating. Carburization from furnace gas (C gas) may occur, and Ti for C, N and S may occur.
Is excessively present, thin TiC is likely to precipitate.

The present invention has been made on the basis of these findings, and the gist thereof is "% by weight, C: 0.0025% or less, S
i: 0.02% or less, Mn: 0.05 to 1.00%, P: 0.030% or less, S: 0.005 to 0.030%, Al: 0.010 to 0.100%, T
i: 0.020 to 0.100%, Cu: 0.010 to 0.100%, N: 0.0
050 to 0.0200%, further satisfying the following formulas (1) and (2), the balance is a slab cast by continuous casting consisting of Fe and unavoidable impurities in the temperature range of 950 to 1150 ℃. A method for producing a cold rolled steel sheet for enamel, which comprises heating, hot rolling, pickling and cold rolling, and then annealing in a temperature range not lower than the recrystallization temperature and not higher than the Ar ₃ transformation point.

Ti ^* (%) / C (%) ≦ 4 (1) However, Ti ^* = Ti (Total) − (48/32) · S− (48/14) · N 2.0 ≦ Cu ( %) / P (%) ≦ 5.0 (2) ”.

[0012]

First, the action and effect of each component contained in the raw steel (slab) used in the present invention and the reason for limiting the content thereof will be described. In addition, "%" of alloying elements means% by weight.

The lower C is, the more advantageous it is to suppress the occurrence of "foam" and improve the moldability. When the C content exceeds 0.0025%, the formability deteriorates, and particularly the drawability (r value) and the elongation decrease, so the content was made 0.0025% or less.

Si has a small effect on the formability and enamel property, but if it exceeds 0.02%, the adhesiveness of enamel may decrease, so the content was set to 0.02% or less.

Mn, like Si, has little influence on the formability and enameling property. Mn is added as described below.
This is to prevent red hot embrittlement due to S and cracks due to it during hot rolling, but if it is less than 0.05%, its effect is not sufficient, and if it is added in a large amount, it only increases the cost. The content was set to 0.05 to 1.00% or less.

[0016] P deteriorates the formability, and if it exceeds 0.030%, its action becomes remarkable, so its content is made 0.030% or less.

S causes cracking during hot rolling. In order to prevent this, a large amount of Mn must be added, which increases the cost, so the upper limit was made 0.030%. The lower limit is preferably lower, but if the content is made to be less than 0.005%, desulfurization treatment is required at the steelmaking stage, and the steelmaking cost increases, so the lower limit was made 0.005%.

Al fixes N as AlN to prevent aging deterioration. However, if it is less than 0.010%, the effect is small and 0.1
If it exceeds 00%, its effect will be saturated and only the cost will increase, so its content should be 0.010-0.100%.
And

As described above, Ti has the effect of fixing C and N and improving the formability of the steel sheet. But 0.020
If it is less than 0.1%, the effect is poor, while if it exceeds 0.100%, the effect of improving the moldability is not recognized, which leads to an increase in cost, so the content was made 0.020 to 0.100%.

Cu is effective in improving the adhesiveness of enamel, but if it is less than 0.010%, the effect is not recognized and 0.100%
If it exceeds, the cost is increased and the formability is lowered. Further, the Cu (%) / P (%) ratio affects the adhesiveness of the enamel, and if the ratio is less than 2.0, it has no effect, and if it exceeds 5.0, the adhesiveness decreases conversely. Therefore, its content is 0.
010 to 0.100% and 2.0 ≦ Cu (%) / P (%)
It was set to ≦ 5.0.

As described above, N reacts with Ti to precipitate TiN, and this TiN occludes hydrogen that has penetrated into the steel plate during firing of enamel and keeps it in the steel, thus suppressing the occurrence of "nail fly". .. However, less than 0.0050% has no effect,
%, The solid solution N is liable to remain, which causes aging deterioration, so the content was made 0.0050 to 0.0200%.

The material steel (slab) used in the present invention has a balance of the contents of Ti, C, N and S so that the content of the individual components described above is satisfied and the following formula (1) is satisfied. It is important to keep

Ti ^* (%) / C (%) ≦ 4 (1) However, Ti ^* = Ti (Total) − (48/32) · S− (48/14)
・ N FIG. 1 shows C and other components as C: 0.0018 to 0.0024%, S
i: 0.006 to 0.018%, Mn: 0.13 to 0.50%, P: 0.008
~ 0.022%, S: 0.008 ~ 0.022%, Al: 0.020 ~ 0.06
Slabs containing 5% range and different Ti ^* (%) / C (%) ratio are heated at 1100 ° C, and the following conditions (condition I), that is, hot rolling finishing temperature: 870 to 920 ° C (Thickness 3.
Winding temperature after hot rolling: 600 to 630 ℃ Pickling: 10% HCl Cold rolling: 3.8 mm → 0.8 mm Annealing: Hot rolling and cold rolling at 800 to 820 ℃ (continuous annealing) The obtained steel sheet was subjected to the following conditions (condition II): pickling: 15% H ₂ SO ₄ , 75 ° C × 10min Ni flash: 13g / l NiSO ₄ , 70 ° C × 5min Glazed: white (Nippon Fellow Co., Ltd. 1553B) Film thickness: Approximately 100 μm per side Firing: A enamel coating was applied directly once at 850 ° C. for 2.5 min, and the result of investigation of the occurrence of “foam” is shown. Evaluation of occurrence of "bubble" was carried out by visual observation of the appearance, of 20 or more within the occurrence number steel sheet surface 20000 mm ² of the "bubble" (100 mm × 200 mm) "large", 6 to 19 pieces Those with 5 or less were designated as "medium".

It can be seen from FIG. 1 that if the Ti ^* (%) / C (%) ratio exceeds 4, "foam" is likely to occur after baking enamel. It is presumed that this is because when the Ti ^* (%) / C (%) ratio exceeds 4, unstable TiC is likely to be formed.

In the present invention, the steel having the above components is melted in a converter, the components are adjusted by vacuum degassing, and the slab is formed by continuous casting, followed by hot rolling, winding, pickling, and cooling. Cold rolled steel sheet for enamel is manufactured through each process of hot rolling, continuous annealing or box annealing. In this manufacturing process, it is possible to heat the slab before hot rolling in an appropriate temperature range.
Is important in suppressing the occurrence of.

In FIG. 2, C: 0.0020%, Si: 0.008%, M
n: 0.13%, P: 0.012%, S: 0.010%, Al: 0.035
%, Ti: 0.040%, Cu: 0.046%, N: 0.0068% after heating the slab at 1000 ~ 1280 ℃, hot rolling, winding, pickling, cold under the above conditions (condition I) It is the figure which showed the result of having investigated the generation | occurrence | production state of "foam" by rolling and annealing, directly applying the enamel coating to the obtained steel plate once once on the same conditions (condition II) as the above. The occurrence of "foam" was visually evaluated and evaluated based on the same criteria as described above.

As shown in FIG. 2, the heating temperature of the slab is 11
If it exceeds 50 ° C, "foam" tends to occur. This is 11
When the slab is heated in a temperature range exceeding 50 ° C, as described above, a large amount of fine and unstable TiC is deposited on the surface of the steel sheet due to the effect of carburization during heating, and this TiC is decomposed during enameling firing. It is presumed that it becomes CO gas, etc., and "foam" is generated. The lower limit of the heating temperature is preferably set to 950 ° C because the end temperature (finishing temperature) of hot rolling is preferably set to 850 ° C or higher.

In the continuous casting of steel, powder (usually carbon powder is added) is supplied into the mold, but if the amount is large, carburization occurs on the surface of the slab, causing "foaming". Therefore, it is desirable to keep the C content in the powder to less than 1.5% by weight.

The annealing may be continuous annealing, but it is preferable to perform decarburizing annealing by a box annealing method. This is to ensure the formability and to prevent the formation of "bubbles" by removing the solid solution C existing on the surface of the steel sheet. For example, steam is blown into a box-shaped furnace for annealing.

If the annealing temperature is lower than the recrystallization temperature (the recrystallization temperature varies depending on the alloy composition, about 600 ° C. for box annealing and about 650 ° C. for continuous annealing), an unrecrystallized structure remains and formability is improved. Significantly decreases, and when the Ar ₃ transformation point is exceeded, α →
Since the γ-transformation occurs and the formability decreases, it is preferable that the temperature is not lower than the recrystallization temperature and not higher than the Ar ₃ transformation point.

[0031]

Example After smelting in a converter, RH vacuum degassing treatment was performed, and a slab having a chemical composition shown in Table 1 was obtained by a continuous casting method (Table 1 also shows the heating temperature of the slab). These slabs are hot-rolled (finishing temperature: 870-920 ° C) into steel strips with a plate thickness of 3.5-4.2 mm, wound at a winding temperature of 580-660 ° C, pickled with hydrochloric acid, and then cold-rolled to 0.7. ~ 1.
It was a 0 mm cold rolled steel sheet. Then, continuous annealing was performed at 780 to 840 ° C.

The cold-rolled steel sheet thus obtained was directly subjected to enamel coating once under the conditions shown in Table 2 to obtain enamel performance ("foam").
The state of occurrence, the adhesion index, and the presence or absence of "nail fly" were investigated. The enamel condition was changed between the evaluation of "foam" generation and the evaluation of adhesion and "flying nails" because "foam" was taken into consideration in consideration of the fluctuation of enamel condition during actual operation.
This is because the condition is such that poor adhesion and "nail fly" are likely to occur.

The occurrence of "foam" was judged by visual inspection. Further, the adhesion index was determined by the PEI method (method prescribed in the US enameled standard), and the presence or absence of "nail fly" was visually checked for the presence or absence of "nail fly" after 2 weeks from baking enamel.

Table 3 shows the results of the enameled performance investigation.

As is apparent from Table 3, the invention examples (No.
Steel sheets 1 to No. 8) showed good enamel performance,
Comparative examples (No. 9 to No. 13) that deviate from the conditions defined by the present invention
At least one of occurrence of "foam" or "nail fly" or poor adhesion was observed on the steel sheet.

Although the examples of direct single-use enamel coating have been described above, the steel sheet used here can of course be used for double-use enamel.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

The cold-rolled steel sheet for enamel produced by the method of the present invention does not generate "foam" after baking enamel, and has good enamel performance such as adhesion and nail flying resistance, and is excellent in formability. Therefore, it is suitable as a material for enamel products that are difficult to form.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the Ti ^* (%) / C (%) ratio and the occurrence status of “bubbles”.

FIG. 2 is a diagram showing a relationship between a heating temperature of a slab and a generation state of “bubbles”.

Claims (1)

[Claims] 1. C: 0.0025% or less, Si: 0.02% by weight
Below, Mn: 0.05 to 1.00%, P: 0.030% or less, S: 0.0
05 to 0.030%, Al: 0.010 to 0.100%, Ti: 0.020 to 0.
100%, Cu: 0.010 to 0.100%, N: 0.0050 to 0.0200%
In addition, the slabs that satisfy the following formulas (1) and (2), and the balance is Fe and unavoidable impurities and are cast by continuous casting are heated in a temperature range of 950 to 1150 ° C, A method for producing a cold rolled steel sheet for enamel, which comprises performing hot rolling, pickling and cold rolling, and then annealing in a temperature range not lower than the recrystallization temperature and not higher than the Ar ₃ transformation point. Ti ^* (%) / C (%) ≦ 4 (1) However, Ti ^* = Ti (Total)-(48/32) ・ S- (48/14) ・ N 2.0 ≦ Cu (%) / P (%) ≤ 5.0 (2)