JPH0711080B2 - High-speed electrolytic melting method for steel metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to carbon steel containing iron and carbon as main components, and further to Ni, Cr,
The present invention relates to a high-speed electrolytic melting method for a surface of a steel metal such as low alloy steel or special steel containing one or more kinds of Mo, Mn and the like.

(Prior Art) When manufacturing a thin plate product by cold rolling a steel metal,
Hot coil obtained by hot rolling is subjected to as-hot rolling or intermediate refining, and then oxide scale generated on the surface during hot rolling or during refining, after mechanical descale treatment such as shot blasting, Manufacture of carbon steel, low alloy steel and ferritic stainless steel by immersing in hydrochloric acid or sulfuric acid solution, and austenitic stainless steel in nitric acid / hydrofluoric acid mixed solution to dissolve and remove scale remaining on the surface, and then cold rolling The law is taking place.

Descale pickling treatment not only completely removes scale, but from the viewpoint of improving the surface quality of steel sheet final products, it is important to dissolve and remove surface defects of hot coils that occur during hot rolling. Have a different role.

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, there is an electrolytic descaling method, and JP-A 64-288, there is a method of immersing in a mixed solution of sulfuric acid and nitric acid.

However, the electrolytic descaling method of Japanese Patent Publication No. 57-2800 is an electrolytic pickling polishing method and an electrolytic treatment method whose main purpose is to dissolve metal in the anode portion rather than the cathode portion.
In the publication, there is a method of immersing in a mixed acid of sulfuric acid and nitric acid without applying electricity, so that when the pickling solution deteriorates due to the interfering action of eluted metal ions, there is a problem that the dissolution of the metal stops. .

(Problems to be Solved by the Invention) From this problem, the present inventors have conducted many experiments and studies on an electrode combination of a cathode and an anode for the purpose of improving the descaling pickling efficiency and smoothing the pickling surface. As a result,
From the result of a single electrode in the indirect energization method, in which the hot coil is changed to the cathode first, and then the polarity is changed to the anode, the results show that it is possible to achieve an unexpectedly large improvement in descaling pickling efficiency and smoothing of the pickling surface. Did.

(SUMMARY for a) The present invention was constructed on the basis of this finding and has as its gist of 5~120g / l of 50 to 100 ° C. NO ₃ ^- ions, or 5
A group in which a steel metal is first made into a cathode in a sulfuric acid aqueous solution having a concentration of 110 to 600 g / l containing ~ 200 g / l of Cr ⁶⁺ ions and then changed to a cathode once or twice as a basic unit. This is a high-speed electrolytic melting method for steel metals, in which a current density of 5 to 200 A / dm ² is applied for cathodic dissolution for cathodic dissolution, and a current density of 35 A / dm ² or less is applied for an anode.

Hereinafter, the present invention will be described in detail.

Dissolution of steel metal in acid solution is an ionization of metal (M → M
^{n +} ＋ ne ⁻ ), and cathodic reaction with reduction of hydrogen ion (2H ⁺ ＋
2e ^- → both reactions of H ₂₎ proceeds by active dissolution to proceed simultaneously. In this case, since the dissolution of the metal proceeds at the spontaneous potential, the dissolved metal ions or Cr ⁶⁺ ions and NO ₃ ⁻ ions raise the corrosion potential from the active dissolution potential region to the passive state potential region, and the dissolution rate Significantly lowers.

On the other hand, under the application of a direct current, the dissolution of the metal at the anode proceeds according to Faraday's law according to the conventional electrochemical theory, but in a sulfuric acid aqueous solution containing Cr ⁶⁺ ions and NO ₃ ⁻ ions. , The dissolution rate of the cathode part reaches several times that of the anode part.

As an electrode combination of the cathode and the anode having such characteristics, figure NO ₃ of 80 ° C. of 45 g / l were dissolved SUS430 of 10 g / l ^- in the aqueous solution containing sulfuric acid ions and 300 g / l SUS430
Measurement of anodic current density dependence of the duration of active dissolution reaction similar to that during cathodic electrolysis of steel during cathodic electrolytic pickling immediately after cathodic electrolytic pickling at a current density of 60 A / dm ² of steel The results are shown.

In addition, Table 1 shows the results of measurement of the fusing capacity and the intergranular corrosion due to Cr deficiency, which were tested under the same conditions as in the figure.

The active dissolution reaction after changing to the anode stops at the same time as changing to the anode at an anode current density exceeding 35 A / dm ² , but when the anode current density is 35 A / dm ² or less, the same active dissolution reaction as during cathode electrolysis. Keeps stable for more than 2 minutes.

The fusing capacity is 35 A / d compared to the anode current density exceeding 35 A / dm ^2.
If it is less than m ² , the amount of fusing is about 4 times larger. In the case of sensitized materials, cold rolling alone with anodic pickling causes intergranular corrosion called fine dust, which causes fine bald marks. A smooth surface can be obtained only with cathodic pickling. Pickling with the combination of the cathode and anode electrodes of No. 1 causes intergranular corrosion at an anodic current density exceeding 35 A / dm ^2, which is the same result as anodic pickling, but at less than 35 A / dm ² , intergranular corrosion occurs. Without using the same pickling time, a very effective effect can be obtained for both the fusing capacity and the smoothing of the pickling surface.

Further, even in the case of SUS304 and high Cr materials, although there is a tendency that the cutting speed of carbon steel, low alloy steel or SUS430 steel is reduced as compared with that, good pickling surface without pickling unevenness is obtained.

A smut, which is a pickling product specific to the active dissolution surface, was observed on the surface after pickling with an anode current density of 35 A / dm ² or less.
It is considered that the active dissolution reaction continued similarly to the cathode electric field because it was not observed at the current density exceeding dm ² .

Such a combination of the cathode and the anode is particularly such that one or two or more pairs of the electrode plates of the anode and the cathode are arranged so as to face the surface of the metal to be pickled of the steel metal, and a direct current is applied between the both electrodes. However, it is particularly effective in the case of the indirect energization method in which the acid-washed metal surface of the steel metal is melted.

Incidentally, in the anode part of the present invention, a phenomenon in which an active dissolution reaction similar to a cathode electric field continues is difficult to explain from conventional electrochemical basic knowledge, but smut which is a reaction product on the cathode dissolution surface is a catalyst. It is considered that the active dissolution of the metal continues even if the metal moves to the anode part.

Regarding the concentration of sulfuric acid, if the concentration is less than 110 g / l, a sufficient effect cannot be obtained at the cathode part, and the stable dissolution capacity cannot be sustained.In addition, if the concentration exceeds 600 g / l, it will dissolve excessively. , The steel surface undergoes pitting-like non-uniform dissolution,
Since it becomes difficult to obtain a uniform surface quality and causes a cost increase, it was set to 110 to 600 g / l.

NO ₃ ^- ion concentration in the range of significant scarfing short acting on the surface of the steel quality metal can be obtained, it can not be expected the effect of such a dark concentrations above concentration also 120 g / l of less than 5 g / l . The Cr ⁶⁺ ion concentration is also within the range where a remarkable shaving action can be obtained in a short time, and at a concentration of less than 5 g / l or a concentration of more than 200 g / l, such an effect cannot be expected.

The temperature is low and the cutting capacity is low, so higher temperature is more desirable, but from the viewpoint of efficiency and equipment resistance, it was set to 50 to 100 ° C.

Regarding the current density of the cathode part in the combination, a sufficient cathodic cutting effect cannot be obtained with a small current density of less than 5 A / dm ² , and a solution with an excessive current density of more than 200 A / dm ^2. Due to the resistance, the liquid temperature suddenly rises and the amount of cathode ablation also becomes saturated.

Therefore, the current density was set to 5 to 200 A / dm ² in order to effectively perform the cathodic electrolysis treatment and to control the temperature of the electrolytic solution.

Note that the current density of the cathode part and the anode part can be controlled by changing the length of the counter electrode to easily control the current density of the anode part of the hot coil to 35 A / dm ² or less. .

The high-speed electric field melting method for a steel metal of the present invention as described above can improve the pickling efficiency and smooth the pickling surface, and achieve continuous high-speed pickling on an industrial scale at low cost.

(Example) Carbon steel, SUS430 containing about 17% of Cr, high Cr ferritic stainless steel containing about 23% of Cr and SUS304 of austenitic stainless steel, a hot coil in which annealing was omitted was used using a mechanically-decayed 10t coil. , 20g / l at 80 ℃
SUS430 steel was melted. 30g / lNO ₃ ^- for the ion -350g / l sulfuric acid, and dissolved depth in the case of performing field pickling by changing the electrode combination of the cathode and the anode, the experiment directly energized by the presence of grain boundary corrosion of the surface I did.

The results are shown in Tables 2 and 3.

The results of indirect energization are shown in Tables 4 and 5.

Furthermore, for 40g / lCr6 ⁺ ion 400g / l sulfuric acid in which 10g / l SUS430 steel was melted at 90 ° C, the results of indirect energization were carried out by changing the electrode combination of the cathode and the anode. It is shown in Table 7.

According to the method of the present invention, all steel types exhibit a high dissolution rate, the descaling pickling efficiency can be improved, and the pickling surface can be smoothed.

(Effects of the Invention) According to the present invention, descaling 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. Therefore, it is possible to remove various kinds of surface flaws generated in the pre-step of pickling under the conditions for controlling the amount of fusing.

Furthermore, since the surface properties of pickling are extremely smooth, their industrial significance in the production of steel metal is extremely large.

[Brief description of drawings]

Figure 1 is 45 g / LNO ₃ containing SUS430 of 80 ° C. of 10 g / l ^- ion -300g / l cathode 60A / dm of SUS430 steel in a sulfuric acid aqueous solution
² is a chart showing the dependence of the active dissolution duration and the anode current density after changing the polarity of the anode at 0 to 70 A / dm ² 120 seconds after the active dissolution for ² 12 seconds.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-1-165800 (JP, A) JP-A-1-316500 (JP, A) JP-A-2-107800 (JP, A) JP-A-3- 107498 (JP, A)

Claims (1)

[Claims] 1. Steel metal in a sulfuric acid aqueous solution having a concentration of 110 to 600 g / l containing 5 to 120 g / l of NO ₃ ⁻ ions or 5 to 200 g / l of Cr ⁶⁺ ions at 50 to 100 ° C. The basic unit is to change the polarity of the cathode first, and then to the anode. Repeat this one or more times. When the cathode is used, the current density of 5 to 200 A / dm ² is applied to melt the cathode. A high-speed electrolytic melting method for steel-based metals, characterized in that 35 A / dm ² or less is anodically melted by applying an electric current.