JP3169872B2 - Continuous annealing pickling method and apparatus for cold rolled 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 method and an apparatus for continuous pickling of cold-rolled stainless steel strip, and more particularly to improving the descalability of a pickling step for removing oxide scale generated during annealing, and The purpose of the present invention is to improve alkali degreasing cleaning performed as a pretreatment for annealing to improve the surface properties of a steel strip, thereby promoting removal of residual alkali and reducing cleaning costs.

[0002]

2. Description of the Related Art In the production of a cold-rolled stainless steel strip, an annealing treatment is applied to the cold-rolled stainless steel strip in order to remove distortion caused by cold rolling. In addition, oxide scale is formed on the surface of the steel strip during the annealing, so that descaling by pickling is performed after the annealing. These treatments are generally performed by a continuous annealing pickling line (cold AP line).

[0003] In the treatment of a cold rolled stainless steel strip by this continuous annealing pickling line, one method of minimizing the formation of oxide scale during annealing is disclosed in Japanese Patent Application Laid-Open No. 6-217.
No. 7 proposes this. This relates to the pre-treatment of the steel strip before annealing. The cold-rolled stainless steel strip has rolling oil, iron powder, etc. during cold-rolling adhered to its surface. In consideration of the fact that the surface is oxidized unevenly, it remains in a pattern even if pickling is performed after annealing and remains inferior in surface quality. To remove those deposits in advance.

[0004]

As described above, if the cold-rolled stainless steel strip before annealing is washed in advance with an alkaline solution to obtain a sufficiently clean surface, it is surely oxidized uniformly during annealing. Oxides can be uniformly removed by pickling after annealing, and a cold-rolled stainless steel strip having excellent surface quality properties can be obtained. However, if the water after the alkali cleaning or the hot water cleaning is not sufficiently performed, an alkali component such as Na ion remains on the steel strip surface. This residual alkali component, particularly in the case of an austenitic stainless steel strip, causes a pattern to appear on the steel strip surface after annealing and pickling, resulting in a problem of deteriorating the surface quality of the steel strip.

In order to solve this problem, it is necessary to sufficiently perform washing with water or warm water after alkali washing.
This requires a large amount of washing water and a large amount of heat source (steam) to heat it. In addition, in the continuous annealing pickling line of a cold-rolled stainless steel strip, when welding with the steel strip of the next coil is performed on the entry side of the line, the entry side line is stopped. The alkaline cleaning liquid adhering to the belt surface is dried and solidified, and cannot be completely removed even after washing with water or hot water.

In order to improve such disadvantages associated with the conventional alkaline cleaning, it is conceivable to use a pretreatment method in a continuous strip plating line for a steel strip as disclosed in JP-A-4-41693. That is, immediately after alkali cleaning for degreasing as a pretreatment step, acid immersion and / or electrolytic pickling is performed to eliminate alkali residues on the surface of the steel strip. However, also in this case, there is a problem that it is necessary to add an acid immersion facility and an electrolytic pickling facility, and a large cost is required.

The present invention has been made in view of the above-mentioned problem of the continuous annealing and pickling of the conventional cold-rolled stainless steel strip, and is easy to quickly neutralize and remove the alkaline cleaning solution on the steel strip surface. Accordingly, it is an object of the present invention to provide a method and an apparatus for continuous annealing and pickling of a cold-rolled stainless steel strip which can obtain good surface quality at low cost.

[0008]

In order to achieve the above object, a method for continuous annealing and pickling a cold-rolled stainless steel strip according to claim 1 of the present invention comprises the steps of: In continuous annealing, waste water of rinsing water that is used to wash the stainless steel strip after the acid cleaning with an acid is used as washing water for washing the stainless steel strip that has been alkali-washed in the degreasing step before the annealing.

Further, a continuous annealing pickling apparatus for a cold-rolled stainless steel strip according to a second aspect of the present invention is a cold rolling apparatus having an alkaline degreasing apparatus upstream of an annealing furnace and a pickling facility downstream. In a continuous annealing pickling apparatus for a stainless steel strip, a washing water storage / supply apparatus for supplying washing water to a washing apparatus located on an outlet side of a degreasing tank of the alkaline degreasing apparatus, and an outlet side of a pickling tank of the pickling equipment And a supply line for supplying wastewater after use in the washing device located in the washing water storage and supply device.

[0010]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an overall schematic configuration diagram of a continuous annealing pickling facility (cold AP line) for a cold-rolled stainless steel strip, and FIG. 2 is a detailed configuration diagram of the alkali degreasing apparatus and the pickling facility. In FIG. 1, a cold-rolled stainless steel strip W that has exited a payoff reel 1 is sent to an alkali degreasing apparatus 3 via a welding machine 2, where it is subjected to alkali degreasing, washing and drying, and adheres to the steel strip surface. Deposits such as rolling oil and iron powder are removed. The details of the alkaline degreasing device will be described later. The degreased stainless steel strip W proceeds in the direction of the arrow A through the entry-side looper 4, is fed into the annealing furnace 5, and is annealed at a predetermined temperature. This annealing is performed, for example, in a direct flame type under an oxidizing atmosphere. The annealing temperature is in the range of 1100 to 1200 ° C. for the austenitic stainless steel strip, and 800 to 90 for the ferritic stainless steel strip.
It is in the range of 0 ° C. During this annealing, an oxide scale is formed on the surface of the stainless steel strip W. The annealed steel strip W is cooled through a cooling zone 6 and then sent to a pickling facility 7 composed of a combination of a neutral salt, nitric acid, nitric hydrofluoric acid, etc., and pickled, so that the steel strip W is annealed during annealing. The oxide scale formed on the surface is removed (descaled). Details of the pickling equipment 7 will also be described later.

The steel strip W rinsed after the pickling is dried by a drier and then wound up on a tension reel 10 via a delivery looper 8 and a shear 9. When the payout of one coil of the pay-off reels 1 installed in a pair is completed, the line is temporarily stopped, and the rear end of the steel strip of the preceding coil and the front end of the steel strip of the other coil are connected to the welding machine 2. Welded.

Next, the details of the alkaline degreasing device 3 and the pickling equipment 7 in the continuous annealing pickling equipment will be described with reference to FIG. The alkali degreasing device 3 is configured by arranging an alkali degreasing tank 12, a first water-washing spray tank 14 and a second water-washing spray tank 15 as a water-washing device, and a dryer 16 in series with a ringer roll 13 therebetween. I have. The alkaline degreasing tank 12 stores, for example, an alkaline solution in which a commercially available alkaline degreasing agent is dissolved. After the steel strip W is immersed in the alkaline solution to remove rolling oil and the like adhering to the surface, the first water-washing spray tank 14 is used.
Then, the alkaline solution remaining on the steel strip surface is washed away through the second washing bath 15. In this case, the second stage
The washing water sprayed in the washing spray tank 15 is clean water or hot water, but in the first washing spray tank 14 in the former stage,
Acidic water is used as washing water. Specifically, an acid water spray tank 17 as a washing water storage and supply device is installed near the first water washing spray tank 14, and the acid water spray tank 17 is provided therewith.
Store the acidic wastewater that is the rinse solution after pickling used in
The water is sucked up by the pump P and sprayed onto the surface of the stainless steel strip W passing through the first washing spray tank 14.

The pickling equipment 7 includes, for example, a two-stage neutral salt electrolytic bath 20, 20 and a pickling bath 21 arranged in series, and further includes a post-pickling rinse bath 22, which is a water washing device, and a drier. 2
3 are arranged in series with the ringer roll 13 interposed therebetween. To illustrate the solution composition of each tank, the neutral salt electrolysis tank 20 stores, for example, a sodium sulfate (Na ₂ SO ₄ ) solution having a concentration of 200 g / l in the tank, and is provided with an electrolysis electrode E which is arranged to face each other. The steel strip W is passed while the electrolysis is performed at a temperature of 70 to 80 ° C. and an electrolytic current of 6 to 10 mA / dm ² . On the other hand, in the pickling tank 21, if the steel strip W is ferritic stainless steel, a simple nitric acid (HN
O ₃ ), and in the case of an austenitic stainless steel strip, a mixed acid (HNO ₃ + HF) of nitric acid at a concentration of 150 g / l and hydrofluoric acid at a concentration of 50 g / l is stored, and the steel strip is immersed at a temperature of 50 to 60 ° C. Let go. As a result, the oxide scale covering the surface of the steel strip is removed. According to the pickling method in which the neutral salt electrolysis method is combined as described above, the handling is easier than the pickling method using the combination of the salt bath and the sulfuric acid electrolysis or the nitric acid electrolysis, and the acid strip does not corrode the metal of the steel strip. There is an advantage that the washing efficiency is good.

The acid solution remaining on the surface of the steel strip W after passing through the pickling tank 21 is removed through the washing water of the rinsing tank 22 after the next pickling. The drainage of the washing water used for the rinse after the pickling becomes acidic water having a pH of about 3 to 5. In the present invention, the acid drainage from the rinse tank 22 after pickling is transferred to the acidic water spray tank 17 installed in the degreasing device 3 through a rinse drainage supply pipe 24 which is a supply line for the drainage. This acidic waste water is used to remove the residual alkaline liquid in the first water-washing spray tank 14.

Thus, the acidic waste liquid of rinsing water used for rinsing adhered acid in the pickling step of the steel strip after annealing is used as the cleaning water for the first rinsing of the steel strip after the alkali cleaning of the pre-annealing treatment. Utilizing, it is possible to quickly neutralize and wash the alkali adhering to the steel strip after the alkali washing. Then, in the second washing step, the finish washing with water or hot water can be easily performed, and a beautiful steel strip free of alkali content can be obtained on the steel strip surface. Generation of a pattern or the like due to an alkali residue on the surface of the steel strip can be suppressed.

Therefore, it is not necessary to use a large amount of water and a large amount of steam in the second washing step as in the prior art, and the running cost can be reduced. Moreover, in order to eliminate the residual alkali on the surface of the steel strip, the alkali degreasing tank 12 must be used.
There is no need to add acid immersion equipment or electrolytic pickling equipment immediately after the above. It is sufficient to simply install the acidic water spray tank 17 and the rinse drainage supply pipe 24, so that the equipment cost can be extremely low.

Further, even if the inlet line is temporarily stopped when welding the steel strip on the inlet side of the continuous annealing line, the alkali adhered to the steel strip surface is dried and solidified during the stop, as in the prior art. However, there is no disadvantage that it cannot be completely removed by washing with water or hot water.

Further, if the acidic drainage from the rinsing tank 22 is used for rinsing the alkaline cleaning liquid after the acid cleaning, the acidic drainage and the alkaline rinse waste liquid are neutralized, and the load of each waste liquid in the water treatment process is reduced. Can be reduced.

Although the pickling method of the present invention has been described in the case where a neutral salt electrolysis method is incorporated in the pickling step, the present invention is also suitable for the case where pickling is performed without using the neutral salt electrolysis method. It can be applied to

[0020]

As described above, according to the present invention,
Since the rinse waste liquid used for rinsing in acid cleaning is used for washing the steel strip with alkali after washing, the alkali on the steel strip surface can be quickly neutralized and washed, and can be washed with the next water or hot water. A beautiful steel strip having no alkali content on the surface can be easily obtained, and even when annealing and pickling are performed thereafter, there is an effect that generation of a pattern or the like due to an alkali residue can be suppressed.

Further, in addition to the above effects, the following various effects can be obtained. Since the usage amount of cleaning water or hot water can be suppressed, the cost of water and steam can be reduced.

[0022] Since a simple modification is sufficient without adding a new washing tank to the existing equipment, the equipment cost can be suppressed. By neutralizing the rinse waste liquid generated in the pickling step and the rinse waste liquid generated in the alkali cleaning step, the load of each wastewater treatment step can be reduced.

[Brief description of the drawings]

FIG. 1 is an overall schematic configuration diagram of a continuous annealing pickling facility for a cold-rolled stainless steel strip according to the present invention.

FIG. 2 is a detailed configuration diagram of the degreasing device and the pickling equipment.

[Explanation of symbols]

 3 Alkaline Degreasing Device 5 Annealing Furnace 7 Pickling Equipment 12 Alkaline Degreasing Tank 14 Rinsing Device (First Rinse Spray Tank) 15 Rinse Device (Second Rinse Spray Tank) 17 Rinse Water Storage and Supply Unit 21 Pickling Tank 22 Rinse Tank (Acid) Rinse tank after washing) 24 Supply line (Rinse drainage supply pipe)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-50-96433 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23G 3/02 C21D 9/56

Claims (2)

(57) [Claims] When continuously annealing a cold-rolled stainless steel strip, the stainless steel strip after the annealing is acid-washed as washing water for washing the stainless steel strip that has been alkali-washed in the degreasing step before annealing. A continuous annealing pickling method for a cold-rolled stainless steel strip, comprising using a waste liquid of a rinse water to be washed. 2. A continuous annealing pickling apparatus for a cold-rolled stainless steel strip having an alkaline degreasing apparatus upstream of an annealing furnace and a pickling equipment downstream, wherein an output side of a degreasing tank of the alkali degreasing equipment is provided. A washing water storage / supply device for supplying washing water to a washing device located therein, and a supply for supplying wastewater used in the washing device located on the exit side of the pickling tank of the pickling facility to the washing water storage / supply device. A continuous annealing and pickling apparatus for a cold-rolled stainless steel strip, comprising: