JP2991646B2 - Steel strip cooling device for descaling stainless steel strip and descaling pretreatment method for stainless steel strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pretreatment for descaling a stainless steel strip, and more particularly, to a method for reducing distortion caused by thermal stress when a thin stainless steel strip is immersed in a salt bath and then washed in a washing tank. TECHNICAL FIELD The present invention relates to a steel strip cooling device for descaling pretreatment of a stainless steel strip which prevents generation thereof, and a descaling pretreatment method.

[0002]

2. Description of the Related Art A pretreatment is performed when an annealed stainless steel strip is immersed in an acid pickling tank for descaling. The pretreatment method differs depending on the pickling method, but in general, in the line for processing hard-to-descale materials, the salt bath method is used as the pretreatment, and when gloss is required, the neutral salt electrolysis method is used. in use. FIG. 2 shows a line configuration when the salt bath method is used as a preprocessing step. The annealed stainless steel strip 1 is placed in a salt bath (NaOH + NaNO ₃ ) at approximately 450 ° C.
After being immersed in the tank 2 and then air-cooled, it enters the washing tank 3 and is washed with water, and is then descaled in the pickling tank. The pickling tank is generally provided with a sulfuric acid tank 13, a mixed acid tank 14, and a nitric acid tank 15, but there are some changes according to the characteristics of the line.

When a high-temperature stainless steel strip heated in a salt bath is immersed in a washing tank, the temperature difference in each part of the steel strip temporarily increases, and thermal stress is generated due to the temperature difference ΔT. . If this exceeds the yield stress of the material, the steel strip will have poor shape or breakage. In particular, a thin steel sheet having a thickness of 0.5 mm or less has a high cooling rate when immersed in a rinsing tank, so that defects due to this thermal stress are likely to occur.

[0004] As a method for solving this shape defect, it is effective to lower the water inlet temperature of the stainless steel strip. Specifically, it is necessary to lengthen the cooling zone from the salt bath to the washing tank or to increase the forced cooling zone. And so on.
On the other hand, it is required to improve the productivity of the annealing and pickling line, and to shorten the cooling zone and improve the forced cooling capacity.

On the other hand, Japanese Patent Laying-Open No. 3-1155591 proposes a method of cooling by air-water spray. According to this method, after immersion in a salt bath, the stainless steel strip is cooled to 250 ° C. or less by air-water spray, and then washed in a water washing tank having a water temperature of 60 ° C. or more to prevent the occurrence of distortion due to thermal stress. Things. However, since the water is cooled while the salt is non-uniformly adhered to the surface of the steel strip, distortion is not eliminated due to the non-uniform cooling. Further, as the temperature decreases, the molten salt solidifies, peels off from the plate surface, and scatters. For this reason, the solidified salt may be scattered, and the spray and the nozzle may be blocked. Further, uneven cooling is promoted, and the generation of distortion is not yet eliminated.

[0006] In some cases, the solidified salt causes dents in the steel strip by the immersion roll.

[0007]

DISCLOSURE OF THE INVENTION The present invention advantageously solves the above-mentioned problems, and a steel strip cooling apparatus for descaling pretreatment of a stainless steel strip capable of preventing a shape defect even with a thin plate having a thickness of 0.5 mm or less. And a pretreatment method.

[0008]

SUMMARY OF THE INVENTION The present invention relates to an apparatus for descaling a stainless steel strip comprising a salt tub and a washing tub, wherein the steel strip is sandwiched between the outlet side of the salt tub and the entrance side of the washing tub. An air header for cooling the steel strip from the front and back surfaces, and a clogging prevention nozzle attached to both ends of the air header, the steel strip cooling device for descaling pretreatment. In particular, the nozzle is a steel strip cooling device for descaling pretreatment, which is a steam and / or water discharge nozzle. Further, the present invention provides a descaling pretreatment method for a stainless steel strip in which a stainless steel strip is immersed in a salt bath and then washed in a water rinsing tank. After cooling to a temperature below the temperature indicated by the following formula with an air header having, a descaling pretreatment method for a stainless steel strip having a thickness of 0.5 mm or less, characterized in that the stainless steel strip having a thickness of 0.5 mm or less is washed with the washing tank. 0.5m thickness to cool to below the temperature shown by the following formula while injecting steam and / or water from the prevention nozzle
m is a pretreatment method for descaling stainless steel strips having a diameter of less than m. Here, the following equation is T = at · t + b, and T:
Steel strip temperature (° C), t: Steel strip thickness (mm), a: Constant (1
80), b: constant (80).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted various studies on shape defects and breakage occurring in a washing tank on the outlet side of a salt bath in a pretreatment step of a descaling line of a stainless steel strip. Knowledge was obtained. The stainless steel strips of various thicknesses were cooled from the outlet side of the salt bath by forced cooling only with air, and immersed in a washing tank. The relationship between the temperature of the steel sheet immediately before immersion in the washing tank and the occurrence of strain (buckling of the sheet) was investigated.
As shown in FIG. From FIG. 3, the buckling is T ≦ 180 · t + 80 (where T: steel sheet temperature ° C.,
If the steel strip temperature is controlled so as to make the thickness t (plate thickness mm), this does not occur. For example, for a sheet thickness of 0.5 mm, buckling can be prevented by cooling to a steel sheet temperature of 170 ° C. or less. By using forced cooling with air, non-uniform cooling does not occur, and dew condensation does not fall on the plate surface,
Further, it is considered that the cooling rate can be easily adjusted when cooling with air, and buckling can be prevented. For this reason, the present invention employs forced cooling using only air. The apparatus of the present invention will be described with reference to FIG.

Annealed stainless steel strip 1 leaving salt tub 2
After removing the salt attached to the surface with a ringer roll 4, the steel strip is cooled to a predetermined temperature by a steel strip cooling device 5 and then dipped in a washing tank 3 to wash the steel strip.
To change to a pickling tank. Steel strip cooling device 5
Are arranged so as to sandwich the steel strip along the steel strip, and are composed of a plurality of air headers 6, nozzle headers 7 and nozzles 8 provided at both ends of the air header 6 (FIG. 1).
(B)).

A plurality of air headers 6 are provided in a direction perpendicular to the traveling direction of the steel strip. The installation pitch is not particularly limited. The air header 6 is provided with an air outlet. The air outlet may be a slit type or a nozzle type. The shape of the slit and the shape of the nozzle are not particularly limited. The nozzle 8 is for removing salt attached to the air header 6 and sprays steam and / or water. Therefore, the nozzle 8 is installed so as to be able to spray from the end of the air header 6 toward the outlet of the air header 6 in the longitudinal direction of the air header 6, that is, in the width direction of the steel strip. This nozzle 8 is provided at the end of the air header 6.
It may be attached via another header 7 or individually without the header 7. Steam is sent to the nozzle 8 via the valve 10 and water is sent to the nozzle 8 via the valve 9. Also, steam and water can be mixed and supplied to the nozzle. The attached salt is easily dissolved at the hydration temperature of the salt, and can be easily removed by spraying water. Since the salt hydration temperature of the salt bath 2 is 50 to 80 ° C., it is effective to use a mixture of water and high-temperature steam.

The injection of the nozzle 8 is determined by the degree of blockage of the air header 6, but may be intermittent or continuous.

[0013]

EXAMPLE After annealing a stainless steel strip having a thickness of 0.2 to 0.4 mm, a NaOH + NaNO ₃ salt bath (temperature 4
(50 ° C.), passed through the steel strip cooling device of FIG. 1 under the conditions shown in Table 1, cooled, and immersed in a water washing tank. As a comparative example,
Without using the steel strip cooling device of FIG. 1, it was cooled by natural cooling from a salt bath and immersed in a washing bath. As a conventional example, after being immersed in a salt bath, it was cooled to 100 to 110 ° C. by steam spray at a steel strip traveling speed of 50 mpm, and then immersed in a water washing tank. Table 1 shows some of the results. FIG. 4 shows the occurrence rate of buckling in each of the example, the conventional example, and the comparative example. It can be seen that according to the present invention, the buckling occurrence rate is greatly reduced.

[0014]

[Table 1]

[0015]

According to the present invention, the non-uniform cooling caused by the non-uniform adhesion of the salt to the steel strip surface, which is generated in the pre-treatment process for descaling, is eliminated, so that the generation of thermal stress can be prevented. In addition, since the salt attached to the cooling device can be removed, the occurrence of strain (buckling) due to thermal stress and the occurrence of press flaws can be significantly reduced in a thin stainless steel strip having a thickness of 0.50 mm or less. .

[Brief description of the drawings]

FIG. 1A is a schematic explanatory view showing a descaling pretreatment apparatus according to one embodiment of the present invention, and FIG.
It is A sectional drawing.

FIG. 2 is a sectional view showing an apparatus for descaling a stainless steel strip.

FIG. 3 is a diagram showing the relationship between the thickness of a steel strip and the temperature before immersion in a washing bath, which affects the occurrence of buckling in the descaling pretreatment of a stainless steel strip.

FIG. 4 is a diagram showing a comparison of buckling occurrence rates.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stainless steel strip 2 Salt bath 3 Rinse tub 4 Ringer roll 5 Steel strip cooling device 6 Air header 7 Header 8 Nozzle 9 Valve 10 Valve 11 Immersion roll 12 Water 13 Sulfuric acid tank 14 Mixed acid tank 15 Nitric acid tank

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C23G 1/32

Claims (4)

(57) [Claims] 1. A descaling pretreatment device for a stainless steel strip comprising a salt tub and a washing tub, wherein the steel strip is disposed so as to sandwich the steel strip on the outlet side of the salt tub and on the entrance side of the washing tub. And a nozzle for preventing clogging provided at both ends of the air header. 2. The steel strip cooling apparatus according to claim 1, wherein the nozzle is a steam and / or water discharge nozzle. 3. A method for descaling a stainless steel strip, wherein the stainless steel strip is immersed in a salt bath and then rinsed in a washing tank, the stainless steel strip having been immersed in the salt bath is provided with a nozzle for preventing clogging. A descaling pretreatment method for a stainless steel strip having a thickness of 0.5 mm or less, comprising cooling the steel sheet to a temperature not higher than the temperature represented by the following formula (1) with an air header, and then washing with a water in the washing tank. T = a · t + b (1) T: steel strip temperature (° C.) t: steel strip thickness (mm) a: constant (180) b: constant (80) 4. The method according to claim 1, wherein the clogging prevention nozzle is provided with steam and / or
4. The method for descaling a stainless steel strip having a thickness of 0.5 mm or less according to claim 3, wherein the stainless steel strip is cooled to a temperature equal to or less than a temperature represented by the following formula (1) while spraying water. T = a · t + b (1) T: steel strip temperature (° C.) t: steel strip thickness (mm) a: constant (180) b: constant (80)