JPH07268670A - Method for pickling stainless steel - Google Patents

Abstract

PURPOSE:To efficiently pickle stainless steel. CONSTITUTION:When stainless steel is pickled, a contact material having baser potential than the potential of the stainless steel by immersion by >=150mV (vsSCE) is brought into contact with the stainless steel in at least the early stage of pickling and ordinary steel or Al is used as the contact material. The stainless steel is efficiently pickled at a low cost without especially requiring large-scale equipment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inexpensive and efficient pickling method for stainless steel.

[0002]

2. Description of the Related Art As a method for pickling stainless steel, there are an immersion method and an electrolytic method. The pickling solution is selected from sulfuric acid, nitric acid, hydrochloric acid, nitric hydrofluoric acid, sodium sulfate and the like according to the type of steel and the manufacturing history of hot working, cold working and the like. In the pickling of stainless steel, since there is a chemically stable Cr oxide, it is not possible to expect the scale removal by melting the scale like ordinary steel, and it mainly depends on the melting of the base material just below the scale. . Therefore, pre-treatment is essential to efficiently perform pickling of stainless steel, and mechanical processing such as shot blasting and spraying of high-pressure water containing sand iron and bending are performed on hot-worked materials, and scale processing is performed. Most scale is removed by cracking.

On the other hand, in the case of the material heat-treated after cold working, the scale is modified by a chemical method such as molten alkali treatment or neutral salt electrolytic treatment, that is, Cr in the scale is dissolved to form a higher-order Fe oxide. Then, the scale is reduced and dissolved together with the dissolution of the base material with the acid solution in the next step.

There are many findings on an efficient pickling method for stainless steel, but they relate to improvement of pickling solution composition, scale modification and production inhibition. As a method for accelerating the reaction rate in the pickling solution, JP-A-57-16
In Japanese Patent No. 8721, a method of grinding a steel sheet end portion with a brush in a pickling solution, and in Japanese Patent Laid-Open No. 2-59214, a method of simultaneously adding mechanical grinding and electrolytic addition in an electrolytic solution is also disclosed. No. 235584 discloses a method of applying ultrasonic waves during pickling. However, these methods have the drawback that large-scale equipment is required.

[0005]

[Problems to be Solved by the Invention]
The present invention provides a more efficient pickling method on an industrial scale that does not require large-scale equipment, that is, an efficient pickling method in which a dissolution reaction is started in an acid solution in a short time.

[0006]

The present invention has been completed as a result of earnest research on an efficient method for pickling stainless steel which solves the above problems. The gist thereof is that, in the pickling treatment of stainless steel, a contact material having a base potential of 150 mV (vs SCE) or more than the immersion potential of the stainless steel is brought into contact with the stainless steel at least in the initial stage of the pickling treatment. . Further, carbon steel or aluminum is desirable as the contact material.

[0007]

The operation of the pickling method of the present invention will be described below. As described above, pickling of stainless steel is generally performed by a dipping method, a spray method or an electrolytic method in a pickling solution after mechanical or chemical preliminary descaling treatment. Among them, in the electrolysis method, since the base material is dissolved by applying an electric current, the material to be pickled immediately starts the dissolution reaction. On the other hand, in the immersion method and the spray method, even if the acid solution is touched, it is not immediately dissolved, and it takes time (τ) until the active dissolution reaction is started. This time reduces productivity. This tendency is remarkable in the austenitic stainless steel containing Ni and the highly corrosion-resistant ferritic stainless steel containing high amounts of Cr and Mo and containing Cu.
The present inventor has focused on shortening the time (τ) at which this active dissolution reaction is initiated.

With reference to FIG. 1, it will be explained that when a metal having a base potential of 150 mV (vs SCE) or more is brought into contact with the immersion potential of stainless steel, the melting start time (τ) can be shortened. At this time, the pickling start time (τ) was defined as the pickling start time by measuring the time until the generation of hydrogen gas generated by the dissolution of the stainless steel. When the immersion potential difference between the stainless steel and the contact material was 150 mV (vs SCE) or more, the pickling start time was drastically shortened. The immersion potential difference is 150 mV (vsSC
In the above E), the time required to start pickling for 2 seconds is the time until the contact material starts to dissolve. The metal used as the contact metal has an immersion potential of 150 mV (vs SCE) compared to stainless steel.
As long as it is a base metal, ordinary steel or Al is preferable. M
Although g, Zn, etc. are also effective, they cause deterioration of the acid because they have a high reaction rate with acid. The area ratio of stainless steel to contact metal is preferably about 100: 1 or more.

[0009]

【Example】

(Example 1) As shown in FIG. 2, SUS304 and S
Ordinary steel (SS400) 2 is spot-welded on the top of the cold-rolled annealing coil 1 of US430 (Fig. C), 10% nitric acid + 5% hydrofluoric acid, dipping bath 3 of a nitric hydrofluoric acid bath at 50 ° C or It is introduced into the spray tank 4. Table 1 shows the pickling start time (τ) as compared with the conventional method in which no contact material was used. Table 1 No. When the ordinary steel according to the present invention method of 1 to 4 is spot-welded to the stainless steel coil and brought into contact with the stainless steel coil, the pickling start time (τ) is 2 to 3 seconds. 9, 1
The pickling start time (τ) of 0 and 11 required 8 seconds or more, while it was shortened.

[0010]

[Table 1]

Example 2 In pickling of the SUS444 hot extruded steel pipe of FIG. 3, 10% sulfuric acid-2% after salt treatment
The steel pipe 1 was immersed in a pickling tank of hydrofluoric acid, 40 ° C., 20% sulfuric acid, and 80 ° C. and suspended by a crane 6. In the method of the present invention, Al, Zn, and ordinary steel (SS400) wire rods 2 were hung on and contacted with a stainless steel pipe before immersion.
Table 1 shows the pickling start time (τ) as compared with the conventional pickling method. Conventional method of immersion of stainless steel alone No. In Nos. 12 and 13, the pickling start time (τ) requires 8 seconds or more.
o. For 5, 6 and 7, it was 2-3 seconds, which was a significant reduction.

[0012]

As described above, according to the method of the present invention, it is possible to carry out pickling of stainless steel inexpensively and efficiently without requiring any equipment cost, and the industrial advantage is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a pickling start time (τ) and an immersion potential difference.

2A and 2B are views showing a method of pickling a stainless steel plate coil, and FIG. 2C is a diagram showing a state in which a contact material is attached to the steel plate.

FIG. 3 is a diagram showing a method of pickling a stainless steel pipe.

[Explanation of symbols]

 1 Stainless steel 2 Contact material 3 Pickling tank 4 Spray tank 5 Pump 6 Crane

Claims (2)

[Claims] 1. In pickling treatment of stainless steel, a contact material having a potential lower than the immersion potential of the stainless steel by 150 mV (vs SCE) or more is brought into contact with the stainless steel at least in the initial stage of the pickling treatment. Pickling method for stainless steel. 2. A method for pickling stainless steel, characterized in that in pickling stainless steel, carbon steel or aluminum is brought into contact with stainless steel at least in the initial stage of pickling.