JPH0711079B2 - High-speed cathodic electrolytic dissolution method for steel metal - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to carbon steel containing iron and carbon as main components, and further Ni,
The present invention relates to a high-speed cathodic electrolytic dissolution method for a surface of a steel metal such as a low alloy steel or a special steel containing one or more of Cr, Mo, Mn and the like.

Conventional technology When manufacturing thin plate products by cold rolling steel metal,
After hot-rolling the hot coil obtained by hot rolling or after performing intermediate refining, after subjecting the oxide scale generated on the surface during hot rolling or during refining to mechanical descale treatment such as shot blasting, Carbon steel, low alloy steel and ferritic stainless steel are immersed in an aqueous solution of hydrochloric acid or sulfuric acid, and austenitic stainless steel is immersed in a mixed aqueous solution of nitric acid and hydrofluoric acid to dissolve and remove scale remaining on the surface, and then cold rolling is performed. There is.

Descaling pickling treatment not only completely removes scale but also dissolves and removes surface defects of hot coils generated during slab heating or hot rolling from the viewpoint of improving the surface quality of steel metal sheet final products. Has an important role to do.

Therefore, development of a high-speed metal dissolution treatment method is required from the viewpoint of improving the descaling pickling efficiency and smoothing the pickling surface. As such an efficient pickling method, Japanese Patent Publication No.
-2800, electrolytic descaling method, JP-A-64-288, dipping in a mixed acid of sulfuric acid and nitric acid.

However, the electrolytic descaling method of Japanese Patent Publication No. 57-2800 is an electrolytic pickling and electrolytic treatment method whose main purpose is to dissolve the metal in the anode portion rather than in the cathode portion. The method of immersing in a mixed acid with nitric acid has a problem that the dissolution of metal is completely stopped when the pickling solution is deteriorated due to the interfering action of eluted metal ions.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The inventors of the present invention have conducted many experiments for the purpose of developing a cathodic electrolytic dissolution treatment method for preventing a decrease in dissolution rate due to eluted metal ions and stably performing continuous pickling operation for a long time. As a result of repeated studies, it was found that the intended purpose can be achieved by cathodic electrolysis treatment in a sulfuric acid aqueous solution containing nitric acid.

The present invention has been completed based on this finding.

Means and Actions for Solving the Problems The present invention provides a sulfuric acid aqueous solution having a temperature of 50 to 100 ° C. and a concentration of 110 to 600 g / l containing 5 to 120 g / l of NO ₃ ⁻ ions,
High-speed cathodic electrolytic melting of steel metal, characterized in that a steel metal is used as a cathode, and a current density of 5 to 200 A / dm ² is applied between the steel metal and the anode provided opposite to the cathode to melt the cathode. Is the law.

Hereinafter, the present invention will be described in detail.

Dissolution of a steel metal in an acid solution is an ionization (M → M
and ^{n +),} the reduction of hydrogen ions as a cathode reaction (2H ^{+ +} 2e ^- →
Both reactions of H ₂ ) proceed at the same time by active lysis. In this case, the dissolution of the metal proceeds at the natural potential,
Metal ions or NO ₃ was eluted ^- ions increases the corrosion potential of the active dissolution potential region in the passivation potential range, significantly reduce its dissolution rate. In contrast, under energization of direct current, the dissolution of the metal in the anode can proceed according to the law of conventional electrochemical theory as Faraday, NO ₃ ^- in the sulfuric acid aqueous solution containing ions, dissolution of the cathode portion The speed reaches several times that of the anode part.

Fig. 1 shows the results of electrolytic pickling treatment in a 300g / l sulfuric acid aqueous solution in which 25g / l SUS430 was dissolved (90 ° C) under conditions of natural immersion of SUS430 steel and at a current density of 60A / dm ² . 2 shows the results of measuring the nitric acid content dependency of the dissolution depth in the anode part and the cathode part per minute of the steel. No metal dissolution is observed under natural immersion conditions. On the other hand, the dissolution depth in the anode part does not depend on the nitric acid content at all, but in the cathode part, it increases with the nitric acid content,
The nitric acid content of g / l reached almost four times that of the anode part, and then decreased rapidly, and became almost the same as that of the anode part at a nitric acid content of about 120 g / l. With respect to such a remarkable increase in the dissolution rate in the cathode part, the same effect can be obtained by adding not only nitric acid but also a nitrate such as sodium nitrate.

On the other hand, in order to make such a cathodic electrolytic dissolution method a practical process, it is essential to maintain the initial dissolution rate for a long time. Generally, in the pickling process of steel metals, the acid concentration is strictly controlled because the dissolution capacity decreases as the concentration of the acid in the pickling solution decreases as the metal dissolves. It is difficult to avoid a decrease in the dissolution rate due to interference.

On the other hand, in the cathodic electrolytic dissolution method in a nitric acid aqueous solution containing nitrate ions according to the present invention, the amount of the eluted metal that is usually used as a guide for the amount of the eluted metal that renews the sulfuric acid pickling solution.
Even at 85 g / l, it is possible to maintain the dissolution capacity of 80% or more of the new solution.

Figure 2 shows the amount of metal ions in the SUS430 steel solution when electrolytic pickling was performed at a current density of 60 A / dm ² in a 300 g / l sulfuric acid aqueous solution containing 60 g / l nitric acid at 90 ° C. And 60 sec
It is a measurement of the relationship with the melting depth per hit. The high dissolution rate in the anode part was only about 20% reduction in the capacity even when 85 g / l of metal ion was contained. Fig. 2 also shows the dissolution depth under the condition of natural immersion (dip immersion) in which no direct current is applied. The new solution shows a slightly higher solubility than that of the cathode part, but only a few g / The dissolution of the metal ion completely stops the dissolution of the metal ion.

The metal dissolution reaction at the cathode portion in the present invention is as follows.

Metal dissolution reaction M → M ^{n +} ＋ ne ⁻ Electron consumption reaction 2H ⁺ ＋ 2e ⁻ → H ₂ and NO ₃ ⁻ ＋ 2H ⁺ ＋ e ⁻ → NO ₂ ＋ H ₂ O The reason why the dissolution of metal is promoted is as follows. NO ₃ ^- is reduced to generate NO ₂ gas, and it is considered that the reduction reaction consumes electrons to accelerate the dissolution reaction in which the metal becomes a metal ion. That is, NO
As a result of the reduction reaction, the ₃ ^- ion is released as NO ₂ gas out of the bath and does not remain as an interfering ion.

In the present invention, the temperature of the electrolytic solution is 50 ° C. or less, the cathodic electrolytic solution rate is at the same level as that in the anode, and the higher the solution temperature is, the higher the solution rate is.
From the practical point of view, the temperature was set to 50 to 100 ° C because the deterioration of the tank or piping material is significant above ℃.

Furthermore, NO ₃ ^- for ion concentration, as is clear from Figure 1, the concentration in the cathodic electrolytic dissolution rate of 40~90g / l is the maximum, at a concentration of less than 5 g / l instead of the addition effect is insufficient , The concentration of the electrolytic dissolution of the cathode is at the same level as that at the anode, so the concentration range was 5 to 120 g / l.

Regarding the concentration of sulfuric acid aqueous solution in this case, when the concentration is less than 110 g / l, the cathodic electrolysis part cannot obtain a dissolution depth exceeding that of the anodic electrolysis part, and moreover, the stable dissolution capacity cannot be maintained, and 600 g If the concentration exceeds / l, it will be excessively melted and pitting-like non-uniform dissolution will proceed on the steel surface, making it difficult to obtain a uniform surface quality and increasing the cost. Therefore, in the present invention, the concentration of the aqueous sulfuric acid solution is set to 110 to 600 g / l in order to carry out the ablation of the surface of the steel metal and prevent the pitting-like non-uniform dissolution to obtain a uniform surface texture.

Further, regarding the current density in this case, a sufficient cathode fusing effect cannot be obtained with a small current density of less than 5 A / dm ² ,
At an excessively large current density exceeding 200 A / dm ² , the solution temperature causes a rapid rise in the solution temperature and the amount of cathodic ablation becomes saturated. Therefore, from the viewpoint of effectively performing the cathodic electrolysis treatment and controlling the temperature of the electrolytic solution, the current density is set to 5 to 5.
It was set to 200 A / dm ² .

The above-described cathodic electrolytic dissolution method for steel metal of the present invention can minimize the disturbing action of dissolved metal ions, and achieve long-time continuous high-speed pickling on an industrial scale at low cost.

Example Carbon steel, SUS430 containing about 17% Cr, high Cr ferritic stainless steel containing about 23% Cr and SUS304 of austenitic stainless steel, respectively, the dissolution depth when performing cathodic dissolution at 90 ° C for 60 seconds of the, 50 g / 8 g / LNO was dissolved SUS430 steel l ₃ ^- ion -150g / l sulfuric acid, 20 g / LNO ₃ ^- ion -150g / l table 1 and table 2 for sulfuric acid, of 80 g / l SUS
430 8 g / LNO ₃ dissolved steel ^- ion -300g / l sulfuric acid, 35 g / LNO
₃ ^- Ion -300g / l sulfuric acid, 60 g / LNO ₃ ^- ion -300g / l Table 3 for sulfate, the Table 4 and Table 5 and 50 g / l SUS304
15 g / LNO dissolved steel ₃ ^- ion -550g / l sulfuric acid, 85 g / LNO ₃ ^-
Ion-550 g / l sulfuric acid is shown in Tables 6 and 7.

In the conventional simple immersion without applying the cathode current, when a considerable amount of the dissolved metal ions coexist due to deterioration during use, the dissolution rate of the metal is remarkably low in stainless steels other than carbon steel. Both steel types show high melting rates.

EFFECTS OF THE INVENTION According to the present invention, descaling treatment of all steel materials from carbon steel to ferritic stainless steel and austenitic stainless steel can be carried out in the same pickling tank and the same pickling bath, and simple dipping treatment 3-5 compared to
Since double high-speed lapping is possible, it is possible to remove various surface flaws generated in the previous step of pickling under the lapping amount control conditions.

Furthermore, the adverse effect of interfering metal ions that dissolve in the pickling solution and reduce the pickling capacity during descaling pickling can be reduced to 20% or less, and stable and efficient pickling work can be continued. The surface properties of pickling are also very smooth.

[Brief description of drawings]

Figure 1 shows SUS430 steel at 90 ° C for 60 seconds in the anode and cathode under direct current immersion in a sulfuric acid aqueous solution containing 25 g / l metal ions at a concentration of 300 g / l and DC current density of 60 A / dm ^2. It is a figure which shows the nitric acid concentration dependence of the metal dissolution depth per hit. Figure 2 shows 300g / L of SUS430 steel containing 60g / l nitric acid at 90 ℃.
FIG. 3 is a diagram showing the dependence of metal dissolution concentration on the metal dissolution depth per 60 seconds in an anode and a cathode under natural immersion in a sulfuric acid aqueous solution having a concentration of 1 and current application with a DC current density of 60 A / dm ² .

Claims (1)

[Claims] 1. A temperature of and 5~120g / l at 50 to 100 ° C. NO ₃ ^-
In a sulfuric acid aqueous solution containing ions at a concentration of 110 to 600 g / l, a steel metal is used as a cathode, and a current density of 5 to 200 A / dm ² is applied between the steel metal and the anode provided facing the cathode. , A high-speed cathodic electrolytic dissolution method for steel metal, characterized by cathodic dissolution.