JPH0368799A - Descaling method for cold rolled stainless steel strip - Google Patents

Abstract

PURPOSE:To improve the descaling effect and to decrease required electric energy by physically removing the resulted product formed on a cold rolled stainless steel strip after the steel strip receives an anodic reaction. CONSTITUTION:The cold rolled stainless steel strip 3 is passed in an aq. neutral salt soln. 4 in an electrolytic cell 5 and is descaled by an indirect electrolysis. The steel strip 3 receive the anodic reaction and the oxide scale eluted in the aq. neutral salt soln. 4 is changed to the resulted product of the descaling reaction on progression of the descaling. This product sticks to the surface of the substrate. This product is physically removed by using a brush roll 8, etc., provided behind a negative electrode 2. The reduction deposition reaction of the metal ions in the cathode reaction is suppressed when the strip is subjected to a cathodic reaction thereafter. The descaling is efficiently executed in this way. The time for treatment is thus shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an efficient descaling method for continuously removing oxidized scale from the surface of cold-rolled stainless steel strip.

<Prior Art> -a. When cold-rolled stainless steel strip is subjected to heat treatment such as annealing or quenching in an oxidizing atmosphere, oxide scale is formed on the surface of the steel strip. In order to remove it, descaling treatment is performed.

Pickling using sulfuric acid, nitric acid, nitric-fluoric acid (a mixed acid of nitric acid and hydrofluoric acid), etc. is generally used for descaling, but the oxide scale that forms on cold-rolled stainless steel strips is dense. Because it is so strong, it is difficult to completely descale it. On the other hand, as a pretreatment method to facilitate fII cleaning, immersion treatment in molten alkali salt (salt treatment) or electrolytic treatment in a neutral salt aqueous solution as shown in Japanese Patent Publication No. 12162/1984 have been developed. It has been put into practical use.

<Problem to be solved by the invention> Electrolytic treatment in a neutral salt aqueous solution has the advantages of being easier to obtain a beautiful surface texture than salt treatment, and because the solution is neutral, the working environment is excellent. be. However, in order to obtain the same effect as salt treatment, which has excellent descaling ability, electrolysis requires a large amount of electrical energy and a long electrolysis time, which requires a long electrolytic cell. There are drawbacks such as.

The present invention was made for the purpose of increasing the descaling efficiency, reducing the required electrical energy, and shortening the electrolysis time without sacrificing the advantages of electrolytic treatment in a neutral salt aqueous solution. It is something.

Means for Solving the Problems> The present invention provides a method for descaling a cold rolled stainless steel strip by indirect electrolysis in a neutral salt aqueous solution, after the cold rolled stainless steel strip undergoes an anodic reaction. This is a method for descaling a cold-rolled stainless steel strip, which is characterized by physically removing products and deposits on the surface of the cold-rolled stainless steel strip produced by the reaction.

In general, as schematically shown in Figure 2, cold-rolled stainless steel
Electrolysis in the band's neutral salt aqueous solution 4 is carried out by using an anode 1 and a cathode 2 that sandwich the stainless steel 93 in the electrolytic cell 5 from above and below.
An indirect electrolysis method is adopted in which the wires are arranged in the direction of the rope and a DC voltage is applied between the two poles. When the stainless steel strip 3 passes between the negative electrodes 2, an anodic reaction occurs on the surface of the copper strip, and when it passes between the anode electrodes 1, a cathodic reaction occurs on the surface of the copper strip, and desorption occurs while undergoing both reactions alternately. In Figure 0, which has undergone scale treatment, 6 is a roll provided inside the electrolytic cell 5, and 7 is a roll provided outside the electrolytic cell 5.

In the anode reaction, a descaling reaction mainly involves a reduction reaction of oxide scale. On the other hand, the force sword reaction naturally occurs due to the indirect electrolysis method, but conventionally only the hydrogen gas generation reaction occurs, and although a slight oxidized scale removal effect by hydrogen gas bubbles can be expected, it is not effective for descaling. It was thought that it would make little contribution.

The present inventors focused on the cathode reaction when electrolysis is carried out industrially in a neutral salt aqueous solution, and as a result of detailed investigation and research into the reaction behavior, we found that under the conventional electrolytic treatment conditions. He made the important discovery that the cathode reaction greatly inhibits descaling, and published JP-A-63-1611.
No. 94, JP-A-1-96398, JP-A-1-96399, and JP-A-1-96400.

In other words, the present inventors found that in the neutral salt aqueous solution in which industrial descaling treatment is carried out, C eluted by the anode reaction is
Contains metal ions such as Cr and Fe, and in the cathode reaction in such a solution, in addition to the hydrogen gas generation reaction, metal ions such as Cr and Fe are reduced and firmly adhere to the steel strip surface as scale-like substances. Based on these findings, as a method to improve the efficiency of electrolytic descaling in aqueous neutral salt solutions, the current density in the cathode reaction was increased from normal according to the metal ion concentration in the solution. How to increase the height (Japanese Patent Application Laid-open No. 63-16119
4) and a method combining the electrolysis order, limiting the concentration of hexavalent Cr ions in the solution, and separating the anode and cathode reaction solutions (JP-A-1-96398, JP-A-1-9)
No. 6399 and No. 1-96400).

However, although these proposals have a remarkable effect on improving the efficiency of descaling, the former increases consumption of tBii, and the latter increases equipment costs. 8? a) It has some drawbacks such as the complexity of management.

Therefore, the present inventors conducted a more detailed investigation into the electrolytic reaction in a neutral salt aqueous solution, and as a result, they discovered a method for significantly improving the descaling efficiency by a simple means.

In other words, the present inventors found that in the anode reaction, as the descaling reaction progresses, the oxide scale that is firmly attached to the steel base due to chemical bonds is dissolved, and a part of it is converted into descaling reaction products. This descaling product simply adheres to the surface of the copper strip and is not chemically bonded to the surface of the copper strip, so it can be easily removed by brushing, spraying, etc. After the anode reaction is completed, if this descaling product is physically removed and then subjected to the cathode reaction, the reduction and precipitation reaction of metal ions in the cathode reaction is significantly suppressed, making descaling extremely efficient. I discovered that.

The reason for this is not clear b1, but the porous descaling reaction product inhibits the diffusion of metal ions such as Cr and Fe generated in the main reaction of descaling into the solution, and the Since the descaling reaction product retains a solution with a higher concentration than the average concentration of metal ions, it facilitates precipitation reactions with Cr, Fe, etc. in the next cathode reaction. Therefore, by removing the descaling products after the anode reaction and before the cathode reaction,
This is thought to be because the concentration of Cr and Fe ions in the solution on the surface of the copper strip is lowered, and the precipitation reaction in the cathode reaction is suppressed.

Regarding various conditions such as the type of neutral salt, the concentration of the neutral salt aqueous solution, temperature, pH, and current density in the present invention, conventional conditions can be applied to the present invention.

As neutral salts, Na salts and K salts such as sulfuric acid, nitric acid, and hydrochloric acid can be used alone or in combination; ! The use of sodium chloride is suitable.

The concentration, temperature, and pl+ of the neutral salt aqueous solution are each 100
-300g/l, 70-90°C, pH-2-8 are appropriate. The concentration of hexavalent Cr ions in the neutral salt aqueous solution is 15 g/j! from the viewpoint of descaling properties. The current density is preferably 2 for both anode and cathode reactions.
~15 A/llj is appropriate.

The same process as the conventional process is also applied to the pickling process performed subsequent to the electrolytic process in a neutral salt aqueous solution.

That is, nitric acid immersion or nitric acid electrolysis is mainly applied to ferritic and martensitic stainless steels, and nitric acid immersion is mainly applied to austenitic stainless steels.

<Example> An embodiment of the present invention will be described based on the drawings.

FIG. 1 is a diagram schematically showing an apparatus to which the neutral salt aqueous solution electrolysis method of the present invention is applied.

Figure 1 (6) shows a brush roll inserted after the anode reaction in the conventional method, that is, after the cathode.
) shows an example in which the IT electrode arrangement was changed to reduce the number of installed brush rolls, and the cold-rolled stainless steel strip was raised above the aqueous solution to be brushed. In Figure 1, (■), 1 is a positive electrode, 2 is a negative electrode, 3 is a cold-rolled stainless steel strip, 4 is a neutral salt aqueous solution, 5 is an electrolytic cell, 6 is a roll installed in the electrolytic cell 5, 7 is a roll installed outside the electrolytic cell 5.

8 is a brush roll provided after the negative electrode 2.

Next, a specific example of the present invention will be described in comparison with a conventional example.

#1iJ annealed in an oxidizing atmosphere! 0.9m S
Regarding US 410.5US430 and 5US304, the descaling status was observed using a descaling experimental device during electrolysis in a neutral salt aqueous solution and subsequent pickling treatment. Regarding 5US410, the case where the pickling treatment was omitted was also investigated.

The order of electrolysis in a neutral salt aqueous solution is the second order for the conventional example.
The experiments were carried out using the electrode arrangement shown in the figure, and the electrode arrangement and brush device arrangement shown in Fig. 1 (ω) as the invention example.

As the neutral salt aqueous solution, an aqueous solution of Na, SO, is used,
The concentration of NaxSOn is 200g/j! , hexavalent Cr ion concentration was 5 g/f, pl+ was 5, and liquid temperature was 85°C.

[Example 1] The results obtained for 5US410 are shown in Table 1.

Conventional method N11L1 could be descaled by electrolysis in a neutral salt aqueous solution with a total electrolysis time of 36 seconds and an electrical quantity of 144 coulombs/d-, and nitric acid immersion treatment.

On the other hand, M3 of the present invention has a total electrolysis time of 18 seconds,
Descaling was possible only by electrolysis of a neutral salt aqueous solution with an amount of electricity of 72 coulombs/dll.

Sake 2 treated by the conventional method under the same electrolytic conditions as the present invention had scale residue.

[Example 2] The results obtained for 5US430 are shown in Table 2.

Conventional method Hiroshi 4 has a total electrolysis time of 45.6 seconds and an amount of electricity of 1
Descaling was possible with neutral salt aqueous electrolysis at 83.6 coulombs/dd and nitric acid immersion treatment.

On the other hand, with the method of the present invention (6), descaling was possible with a total electrolysis time and electricity amount of about half of that of the conventional method (4) with neutral salt aqueous electrolysis and nitric acid immersion treatment.

Neutral salt aqueous solution electrolysis and nitric acid under the same electrolytic conditions as the present invention! 2
N115 obtained by the conventional method of immersion treatment left scale residue.

[Example 3] The results obtained for 5US304 are shown in Table 3.Nα7 of the conventional method was desorbed by electrolysis in a neutral salt aqueous solution with a total electrolysis time of 30 seconds and an electricity amount of 120 coulombs/dd, and nitric-fluoric acid immersion treatment. It was possible to scale.

On the other hand, the disadvantage of the method of the present invention is that descaling was possible using neutral salt aqueous electrolysis and nitric-fluoric acid immersion treatment, which took about half the total electrolysis time and electricity of the conventional method.

In case 8 was prepared using the conventional method of performing neutral salt aqueous electrolysis and nitrofluoric acid immersion treatment under the same electrolytic conditions as those of the present invention, scale remained.

<Effects of the Invention> As explained above, the present invention significantly improves the descaling of cold-rolled stainless steel sheets by indirect electrolysis in a neutral salt aqueous solution by adding a simple process to the conventional method. It is possible to reduce processing time and electric energy vI.

Furthermore, the method of the present invention has the versatility of being applicable to any type of stainless steel, such as ferritic, martensitic, and austenitic stainless steels.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1, ω) is a diagram schematically showing an example of an apparatus to which the neutral salt aqueous solution electrolysis method of the present invention is applied. FIG. 2 is a diagram schematically showing a typical example of a conventional neutral salt aqueous solution electrolysis treatment apparatus. 1... Positive electrode, 2... Negative electrode, 3...
・Stainless steel cold rolling me, 4...neutral salt aqueous solution, 6.7...roll, 5...electrolytic bath, 8...rotating brush.

Claims (1)

[Claims] When descaling a cold-rolled stainless steel strip by indirect electrolysis in a neutral salt aqueous solution, the cold-rolled stainless steel strip undergoes an anodic reaction. and a method for descaling a cold-rolled stainless steel strip, the method comprising physically removing deposits.