JPH05295599A - High speed pickling method for steel metal - Google Patents

Abstract

(57) [Summary] [Purpose] It can exhibit high fusing capability for any steel grade.
Moreover, it provides a high-speed pickling method for steel materials, which can obtain excellent surface properties after pickling. [Structure] Pt ion of less than 500 mg / liter, P
It contains one or more of the d ions and Rh ions, and further contains 300 g / liter or less of NO ₃ ^−.
In the pickling method of electrolytically treating a steel metal in a hydrochloric acid aqueous solution containing ions and having a hydrochloric acid concentration of 100 to 450 g / liter and a liquid temperature heated and kept at 50 to 110 ° C., 5
By alternating the anode and the cathode at a frequency of cycle / sec or more, the abrading ability of the pickling solution and the surface smoothness are extremely improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to ordinary steel, Cr, Ni,
The present invention relates to a high-speed pickling method for removing oxide scale formed on the surface of steel metal such as special steel containing Nb.

[0002]

2. Description of the Related Art During cold rolling of a steel sheet, pickling is carried out after mechanical descale treatment such as shot blasting is performed on oxide scale formed on the surface of a hot coil obtained by hot rolling. This pickling treatment not only completely removes scale but also has an important role of dissolving and removing surface flaws to form a smooth surface.

Conventionally, this pickling is performed in a hydrochloric acid or sulfuric acid aqueous solution for low alloy steels and ferritic stainless steels, and in a mixed aqueous solution of nitric acid and hydrofluoric acid for austenitic stainless steels containing Ni. , A pickling solution suitable for the steel type is selected.

The proper use of the pickling solution depending on the steel type is carried out based on the abrading capacity of the pickling solution and the surface properties after the pickling. For example, a steel type containing a large amount of Ni such as sulfuric acid such as austenitic stainless steel has a remarkably low dissolution rate in sulfuric acid, and it takes a long time to obtain the required amount of scraping. When an acid-mixed aqueous solution is used, high fusing capability can be exhibited and the surface properties after pickling are also good. However, this nitric hydrofluoric acid is C
When it is applied to ferritic stainless steel in which the annealing process of the hot coil is omitted, the difference between the grain boundary with a small amount of Cr and the fusing capacity in the grains with a large amount of Cr causes Intergranular corrosion will occur. Therefore, for the pickling of ferritic stainless steel, for example, intergranular corrosion, which is also shown in Japanese Patent Laid-Open No. 59-83783, does not occur, but sulfuric acid having a small fusing capacity is currently used. is there.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to perform high-speed pickling of a steel material capable of exerting a high fusing capability on any steel type and, in addition, obtaining excellent surface properties after pickling. To provide a method.

[0006]

The present invention provides 500 mg /
It contains one or more of Pt, Pd, and Rh ions of 1 liter or less, and has a hydrochloric acid concentration of 1 or less.
In an acid pickling method of electrolytically treating a steel metal in a hydrochloric acid aqueous solution which is heated to a temperature of 50 to 110 ° C. at a temperature of 0 to 450 g / liter, alternating an anode and a cathode at a frequency of 5 cycles / sec or more. Is characterized by.

The hydrochloric acid aqueous solution used in the present invention contains 300 g.
It is also possible to contain less than 1 / liter of NO ₃ ⁻ ions.

When alternating the anode and the cathode, a steel metal, which is the material to be treated, is used as the anode, and a current is passed between the anode and the cathode so that the anode and the cathode are electrically connected. Alternately, one or two or more pairs of electrode plates of an anode and a cathode are arranged in a hydrochloric acid aqueous solution so as to face the surface of the steel metal which is the surface to be pickled, and the two electrodes are repeatedly electrically alternating. Alternating current may be used as the electrical alternation between the anode and the cathode.

The electric density during energization is not particularly limited, but a range of 5 to 200 A / Dm ² is preferable from the viewpoint of efficient and stable long-term ablation. In particular, at an excessive current density exceeding 200 A / Dm ² , the solution temperature rapidly rises due to the solution resistance, and the hydrochloric acid aqueous solution may be severely deteriorated and the steel metal may be overpickled.

[0010]

[Function] Hydrochloric acid has a better ability to dissolve ground iron than sulfuric acid, and has a function of shortening pickling time. However, this functional effect of hydrochloric acid cannot be obtained at any concentration, and at a thin concentration of less than 100 g / liter, the dissolution ability is insufficient and scale remains, so that pickling requires a long time. When it exceeds 450 g / liter, the dissolution capacity reaches supersaturation.

Further, Pt ions, Pd ions and Rh
The effect of adding ions is that the amount of ablation increases as the amount added increases, and descaling is possible in a short time.
It is possible to obtain a smooth pickled surface without causing intergranular corrosion when dissolving a material having r-deficiency. The addition is 1 mg /
Although the addition of a small amount of about 1 liter improves the above-mentioned fusing with hydrochloric acid, an industrially required fusing effect is obtained at 3 mg / l or more. However, excessive addition of 500 mg / liter or more is meaningless because the fusing capacity reaches the supersaturated region.

Further, Pt ions, Pd ions and R
By adding NO ₃ ⁻ ions from nitric acid, NaNO ₃ or the like to the above-mentioned aqueous hydrochloric acid solution containing h ions and having a predetermined concentration, the machinability increases as the nitric acid concentration increases. However, if it exceeds 300 g / liter, intergranular corrosion occurs. In a hydrochloric acid aqueous solution containing NO ₃ ⁻ ions, P
Regarding the ablation ability when t ions, Pd ions, and Rh ions are individually added, the ablation ability is increased by the addition of Pt ions, Pd ions, and Rh ions.

The liquid temperature of the hydrochloric acid aqueous solution having the composition of the present invention becomes smaller as the temperature becomes lower and the melting and cutting capability becomes larger as the temperature becomes higher.
The range of 0 ° C is preferred.

Further, the improvement of the fusing ability by immersing the steel sheet in a pickling solution and applying a potential to the steel sheet is particularly remarkable by the alternation at a frequency of 5 cycles / sec or more, and the time when the steel sheet changes to the anode and the cathode. It was found that the ratio shows a larger capacity than the ablation capacity estimated by apportioning the anode ablation amount and the cathode ablation amount.

FIG. 1 shows the results of examining the relationship between the number of times of switching the anode and the cathode per time and the fusing capacity. In this experiment, the time for switching to the anode and the time for switching to the cathode were made equal. Hydrochloric acid 250 g /
Liter, nitric acid 10g / liter, Pd ion 50mg
/ L, 80 ° C solution, 42 μm / at anode
Min. And cathode, there is 37 μm / min of ablation, and if the time is apportioned, it will be 40 μm / min. If it is less than 5 cycles / sec, it becomes 40 μm / min, which is the same as the apportioned value, but if it is 5 cycles / sec or more, the fusing capacity sharply increases. The surface after pickling was smooth without intergranular corrosion.

Next, FIG. 2 shows the fusing capacity with respect to the current density. At the anode, the fusing capacity increases with the current density,
The cathode shows almost constant fusing capacity regardless of the current density.
Pd ions are positive ions as a mechanism for further increasing the fusing capacity when the switching speed for switching between the anode and the cathode exhibiting such electrical characteristics is increased. Attracted to the surface, Pd
Is likely to precipitate on the steel sheet, and the amount of Pd ions that work effectively at the anode increases, and it is considered that the Pd ion works effectively at 5 cycles / sec or more.

[0017]

EXAMPLE A low Cr steel containing 7% of Cr, C
Chromium-based stainless steel SUS4 containing about 17% r
30, high Cr steel containing 19% Cr, 18% Cr,
S of austenitic stainless steel containing 8% Ni
It was applied to a hot coil with remarkable sensitization without annealing of high-carbon steels of US304, high carbon steel containing 1.2% carbon and 0.4% Cr, and a hot coil of 1 m width and annealed to 10 t.

[0018] These hot coil, then subjected to mechanical descaling of spraying high-pressure water mixed with sand grains, hydrochloric acid concentration, NO ₃ ^- ion concentration, Pt ions,
The ablation ability and the surface aspect were evaluated by changing the addition mode of Pd ions and Rh ions, the heating temperature of the liquid, and the mode of energization.

As the energization method, a coil is used as an anode, and a current is applied between a coil and a cathode provided so as to face the coil, and a direct energization method in which the anode and the cathode are electrically alternating, and a cathode and an anode are used. Width 1400mm, length 400m on one side of steel strip
Two pairs of m, a total of 8 electrode plates, are installed with their polarities vertically symmetrical, the distance between the poles is 30 to 100 mm, and the steel strip has a basic polarity of +-, We adopted an indirect energization method that energizes the current between the poles so that it becomes-+-+,-+, +-.

The number of cycles / sec of each alternation and, further, the fusing depth when the frequency was changed when alternating current was used was taken as the fusing capacity for 1 minute, and this and the presence or absence of intergranular corrosion on the surface were determined. evaluated.

Table 1 shows the test and the results.

[0022]

[Table 1] As is clear from this table, according to the method of the present invention, the application of the alternating electrode shows a high fusing rate in any of the steel types, improves the descaling pickling efficiency, and smoothes the pickling surface. We were able to.

The pickled steel strip thus obtained together with a comparative material has a large diameter roll (work roll having a diameter of 200 to 600 mm).
Cold rolling process by a combination of tandem cold rolling by a rolling mill train having the above and cold rolling by a Sendzimir mill having a small work roll (work roll having a diameter of 100 mm or less), and cold rolling only by the Sendzimir mill (3t → 0.4t ) And then bright annealing was performed.
The product plate thus obtained was tested for gold dust (generated if there was intergranular corrosion of the pickled plate). As a result, no gold dust was generated and the surface gloss was good.

[0024]

The following effects can be obtained by applying the electrode alternation according to the present invention.

(1) The treatment capacity per pickling solution is increased, and the amount of waste liquid discarded after the pickling can be reduced.

(2) Significantly improved pickling and shaving effect and surface smoothing after pickling were obtained, and pickling treatment can be made much faster.

(3) Depending on the type of steel used, it is not necessary to switch the pickling solution, and the utilization factor of equipment is improved.

(4) The washing water required when switching the pickling solution is not required, and water resources can be saved.

(5) The pickling product can be recovered together with hydrochloric acid in a hydrochloric acid roasting facility, and industrial waste can be reduced.

(6) The use of hydrofluoric acid, which is highly harmful, can be eliminated.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the number of cycles of switching between an anode and a cathode and the fusing capacity.

FIG. 2 is a diagram showing a relationship between current density and ablation capacity.

Claims (2)

[Claims] 1. One or two of Pt ion, Pd ion, and Rh ion of 500 mg / liter or less.
5 cycles / sec or more in the pickling method of electrolytically treating a steel metal in a hydrochloric acid aqueous solution containing at least seeds and having a hydrochloric acid concentration of 100 to 450 g / liter and a liquid temperature heated and kept at 50 to 110 ° C. A method for high-speed pickling of steel metal in which an anode and a cathode are applied with an alternating potential. 2. The high-speed pickling method for steel metal according to claim 1, wherein the hydrochloric acid aqueous solution contains 300 g / liter or less of NO ₃ ⁻ ions.