JPH10259489A - Descaling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obviate the generation of sludge contg. hexed chromium and gaseous NOx and to enable good descaling even without a salt treatment depending up the characteristics of scale by treating a material required to be descaled with an alkaline permanganic acid liquid., then treating the material with mixed acids consisting essentially of hydrochloric acid, sulfuric acid or a liquid mixture composed of both and contg. non-water soluble carboxylic acid and surfactant. SOLUTION: For example, the material required to be descaled is immersed into the alkaline permanganic acid liquid heated to 50 deg.C to a b. p., by which the chromium oxide, etc., in the scale hardly soluble in the acid are oxidized and are reformed to the substances having good solubility. The material required to be descaled is thereafter immersed into the mixed acids which consist essentially of the hydrochloric acid, sulfuric acid or the liquid mixture composed of both, contains the non-water soluble carboxylic acid and the surfactant, contains, in some cases, a hydrofluolic acid or a small quantity of nitric acid or nitric acid component and water-soluble carboxylic acid and are heated to 30 to 80 deg.C. As a result, the scale of the steel kinds and the heat histories which are hardly removable by the inorg. acids alone are completely removed. The descaling with the uniform dissolution and the improved surface quality is thus made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a scale produced by hot rolling or heat treatment of stainless steel or the like.
The present invention relates to a descaling method suitable for removing (that is, descaling) a scale of a material and a heat history which are difficult to remove by an ordinary method by pickling.

[0002]

2. Description of the Related Art In general, descaling of stainless steel or the like is usually performed by a combination of a relaxation treatment of the scale with a molten salt (hereinafter referred to as "salt treatment") and an acid washing with a mixed acid of nitric acid and hydrofluoric acid. Often implemented.

[0003]

However, in the salt treatment, a salt such as sodium hydroxide is heated and melted at a high temperature, and the descalable material is immersed in the molten salt. In addition to environmental problems such as generation of sludge containing hexavalent chromium, there are also problems in facilities such as a processing tank and a heating tube that are easily damaged and require maintenance.

In addition, a mixed acid of nitric acid and hydrofluoric acid may generate nitrogen oxides (NOx gas) during pickling, significantly deteriorating the working environment and, when waste liquid is used, a high concentration of dissolved nitrogen. Since there is a problem that waste liquid treatment is difficult, it has been a problem to develop an alternative applicable descaling method that does not involve such a problem.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a method for producing nitrogen oxides (N
An object of the present invention is to provide a descaling method capable of preventing generation of Ox gas), easily treating a waste liquid, and desirably descaling without salt treatment depending on the scale properties.

[0006]

The descaling method according to the present invention comprises, as described in claim 1, treating a descalable material with an alkaline permanganic acid solution and then adding hydrochloric acid or sulfuric acid or both. It is characterized in that it is treated with a mixed acid containing a mixture as a main component and containing at least a water-insoluble carboxylic acid and a surfactant.

[0007] In an embodiment of the descaling method according to the present invention, as described in claim 2, claim 1 is provided.
The mixed acid according to the above can be treated with a mixed acid containing hydrofluoric acid, or as described in claim 3,
The mixed acid according to claim 1 or 2 can be treated with a mixed acid containing a small amount of nitric acid or a nitric acid compound (ie, an amount that does not generate nitrogen oxides (NOx gas) during descaling). Alternatively, as described in claim 4, the mixed acid according to claim 1, 2, or 3 can be treated with a mixed acid containing a water-soluble carboxylic acid. The descaling method described in any one of (4) to (4) can be appropriately repeated or performed in combination.

[0008] Similarly, in an embodiment of the descaling method according to the present invention, as described in claim 5,
Redox potential (ORP) of alkaline permanganate liquid bath
Is preferably maintained at 350 mV or more. In this case, as described in claim 6, in the component ratio between Mn ⁶⁺ and Mn ⁷⁺ in the alkaline permanganate liquid bath, the ratio of Mn ⁷⁺ If the ratio is 75% or more,
Redox potential (ORP) of alkaline permanganate liquid bath
Can be maintained at 350 mV or more, or as described in claim 7, the alkaline permanganate solution bath is subjected to a regeneration treatment (electrolysis treatment). Mn ⁶⁺ and Mn in
^{With respect} to the component ratio with ⁷⁺ , the ratio of Mn ⁷⁺ can be maintained at 75% or more.

The descaling method according to the present invention has the above-described configuration, and will be described in more detail below.

[0010] 1. In the descaling method according to the present invention,
First, the descalable material is treated with an alkaline permanganate solution. The alkaline permanganate solution will be described.

◎ Alkaline permanganate solution As the alkaline permanganate solution, for example, sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium carbonate (Na ₂ CO ₃ ), potassium carbonate (K ₂ C)
O ₃ ), a total of one or more selected from 0.1 to 3.0 mol / l, sodium permanganate (NaMnO ₄ ), potassium permanganate (KMn)
O ₄ ), the total of one or two selected from 0.
A solution containing 1 to 2.0 mol / l can be used.

Then, this solution is heated to 50 ° C. to the boiling point to subject the descalable material to, for example, immersion treatment.

2. In the descaling method according to the present invention,
After treatment with the alkaline permanganate solution,
Hydrochloric acid or sulfuric acid or a mixture of both as a main component and contains at least a water-insoluble carboxylic acid and a surfactant,
In some cases, the treatment with a mixed acid containing appropriate components such as hydrofluoric acid, a small amount of nitric acid or a nitric acid compound, or a water-soluble carboxylic acid is performed. The treatment with the mixed acid will be further described.

塩 酸 Hydrochloric acid or sulfuric acid or a mixed solution of both The hydrochloric acid or sulfuric acid or a mixed acid of both contributes to dissolution of FeO in the scale and a base immediately below the scale, and is therefore a main component in the pickling solution.

If the amount of hydrochloric acid or sulfuric acid or a mixed acid of both is small, the time required for pickling tends to be long. Therefore, it is more preferable that the amount is 5 wt / vol% or more. Even if it is too long, the improvement of the descaling speed tends not to be obtained so much.
t / vol% or less, more preferably 10 to 2%.
More preferably, it is 5 wt / vol%.

Water-insoluble carboxylic acid Water-insoluble carboxylic acid reacts with a surfactant to make it water-soluble, thereby forming a chelate with a dissolved metal ion, thereby forming a metal ion in the vicinity of the surface of the substrate. Since it is an agent that contributes to preventing the occurrence of rough skin and pitting due to the concentration of the acid, it is added to the pickling solution in an appropriate amount.

Such a water-insoluble carboxylic acid is selected from the first group (having a benzene nucleus) and the second group (having a straight chain) as exemplified in Table 1. You can choose to use.

[0018]

[Table 1]

In this case, if the amount of the water-insoluble carboxylic acid is small, the effect of preventing skin roughness and pitting due to the concentration of metal ions near the surface of the base material is not sufficient, so that 0.01 wt / vol% or more. More preferably, the content is more preferably 0.1 wt / vol% or more. However, since foaming increases when blended more than necessary, the content is more preferably 1.0 wt / vol% or less. More preferably, the content is 0.2 wt / vol% or less.

Surfactant Since the surfactant is a component that contributes to the water-solubility of the water-insoluble carboxylic acid, it is appropriately added to the pickling solution.

And, as such a surfactant,
It can be appropriately selected and blended from anionic or nonionic compounds as exemplified in Table 2.

[0022]

[Table 2]

In this case, the amount of the surfactant is desirably equal to or more than the concentration necessary for making the water-insoluble carboxylic acid soluble, that is, the concentration of the water-insoluble carboxylic acid. Since the foaming increases when blended as described above, it is more preferable to set the concentration of the water-insoluble carboxylic acid to about three times or less.

◎ Hydrofluoric acid It is possible to use a pickling solution in which hydrofluoric acid is added to a mixed acid containing hydrochloric acid or sulfuric acid or a mixture of both as a main component and at least a water-insoluble carboxylic acid and a surfactant. The hydrofluoric acid contributes to the dissolution of hydrofluoric acid-soluble components such as SiO ₂ in the scale and the improvement of the permeability of the mixed acid.

Accordingly, in some cases, this hydrofluoric acid can be mixed in an appropriate amount in the mixed acid. However, if the mixing amount is too large, the effect cannot be improved so much.
1% or less (that is, in the range of 0 to 10 wt / vol%)
It is preferable to set the weight to 5 wt / vo from the viewpoint of economy.
1% or less (that is, in the range of 0 to 5 wt / vol%).

◎ A small amount of nitric acid or nitric acid compound In a mixed acid containing hydrochloric acid or sulfuric acid or a mixture of both as a main component and at least a water-insoluble carboxylic acid and a surfactant, and optionally hydrofluoric acid as described above. It is also possible to prepare a pickling solution containing a small amount of nitric acid or a nitric acid compound in a mixed acid containing
It is effective in controlling the oxidation-reduction potential (ORP) and contributes to keeping the oxidation-reduction potential in the active dissolution potential region.

The nitric acid or nitric acid compound can be appropriately selected from those exemplified in Table 3 and blended.

[0028]

[Table 3]

In this case, if the compounding amount of nitric acid or a nitric acid compound is too large, nitrogen oxides (NOx gas) are generated at the time of pickling, or a waste liquid having a high concentration of dissolved nitrogen cannot be obtained to satisfy the waste liquid treatment standard. Therefore, it is necessary to take a countermeasure against dissolved nitrogen. Therefore, 1 w which is smaller than the generation level of nitrogen oxides (NOx gas) as nitrate is small.
t / vol% or less (that is, in the range of 0 to 1 wt / vol%), more preferably 0.1 to 0.2 wt%.
/ Vol% is more desirable.

Water-soluble carboxylic acid In a mixed acid containing hydrochloric acid or sulfuric acid or a mixture of both as a main component and at least a water-insoluble carboxylic acid and a surfactant, and in some cases, hydrofluoric acid and / or Alternatively, a pickling solution containing a water-soluble carboxylic acid in a mixed acid also containing nitric acid or a nitric acid compound can be used, but the water-soluble carboxylic acid is formed by forming a complex salt with a dissolved metal ion. This contributes to improving the life of the pickling solution.

Such a water-soluble carboxylic acid can be suitably selected from those exemplified in Table 4 and blended.

[0032]

[Table 4]

In this case, even if the amount of the water-soluble carboxylic acid is too large, the effect is not so much improved, and considering the economical efficiency, 10 wt / vol% or less (that is, 0 to 0%).
More preferably, it is set to 10 wt / vol%.

3. In the descaling method according to the present invention,
The above 1. The treatment with an alkaline permanganate solution described in 2) and However, when the treatment weight increases, as shown in FIG. 1, the oxidation-reduction potential (ORP value) of the alkaline permanganate liquid bath gradually decreases.

The decrease in the oxidation-reduction potential is due to the deterioration of the alkaline permanganate solution. If the oxidation-reduction potential is lower than 350 mV, the descaling property is reduced, and the descaling becomes difficult. That and pitching may occur.

Therefore, it is desirable to maintain the oxidation-reduction potential of the alkaline permanganate liquid bath at 350 mV or more.

On the other hand, when the relationship between the oxidation-reduction potential and the component ratio of Mn ⁶⁺ and Mn ⁷⁺ in the alkaline permanganate solution bath was examined, it was confirmed that the relationship was as shown in FIG.

Therefore, if the proportion of Mn ⁷⁺ is 75% or more in the component ratio of Mn ⁶⁺ and Mn ⁷⁺ , the oxidation-reduction potential can be maintained at 350 mV or more, so that the deteriorated alkaline excess It is desirable to perform a regeneration treatment (electrolytic treatment) on the manganic acid solution.

Here, the principle of descaling and the deterioration of the alkaline permanganate solution due to the descaling (Mn
(Change from ⁷⁺ to Mn ⁶⁺ ) is shown in equation 1, and the regeneration principle (electrolytic oxidation) of the alkaline permanganate solution bath is shown in equation 2.
Shown in

[0040]

(Equation 1)

[0041]

(Equation 2)

In the regeneration treatment (electrolysis treatment) of the deteriorated alkaline permanganate solution bath, for example, a voltage of 10 to 20 is applied between a plurality of parallel electrodes installed in the bathtub.
V, current density: 300 to 1200 A / m ² , desirably, about 500 to 800 A / m ² can be applied by applying a direct current, and the alkaline permanganate solution is recycled and used by a closed system. This eliminates the need for waste liquid treatment and allows for economical descaling.

[0043]

In the descaling method according to the present invention, the descaling material is first immersed in, for example, an alkaline permanganate solution heated to, for example, 50.degree. Object (Cr
₂ O ₃ ) or the like is oxidized and reformed into a substance having good solubility (see the above formula 1), and thereafter, an interface is formed with a water-insoluble carboxylic acid mainly containing hydrochloric acid or sulfuric acid or a mixture of both. For example, 30 to 8 containing an activator and optionally further containing hydrofluoric acid, a small amount of nitric acid or a nitric acid compound or a water-soluble carboxylic acid.
By immersion treatment in a mixed acid heated to 0 ° C., for example, steel types and scales of heat history that are difficult to remove with inorganic acids alone are completely removed, and the finished surface is free from defects such as rough skin and pitching due to uniform dissolution. A descaling with considerably improved quality will be performed.

[0044]

EXAMPLE In this example, an example of descaling in which a treatment with an alkaline permanganate solution and a treatment with a mixed acid solution containing a water-insoluble carboxylic acid are performed, and the salt treatment is omitted will be described.

That is, the austenitic stainless steels SUS XM7, SUS 316, ferritic stainless steel SUS 430, and martensitic stainless steel SUS 403 as shown in Table 5 were used as target steels, and the history shown in Table 5 (that is, the thermal history) (Steel rolling, solution heat treatment, annealing), an immersion treatment was performed under the alkaline permanganate treatment conditions also shown in Table 5, using an alkaline permanganate solution having the bath composition shown in Table 5. .

As shown in Table 5, the permanganic acid decomposition treatment with a 13% HCl solution is performed because, when the alkaline permanganic acid treatment is performed, the surface reacts with permanganic acid to generate permanganic acid. Oxide (Mn
⁶⁺ , Mn ⁴⁺ ) and the like, which are still oxidizing. Therefore, if they are immersed in a pickling solution, they may oxidize organic acids and the like in the mixed acid. This is for decomposing (reducing to Mn ²⁺ ) permanganic acid and the like.

Next, using a mixed acid having the composition shown in Table 6,
The immersion treatment was performed under the mixed acid treatment conditions shown in FIG.

When the descaling state after the descaling treatment was examined in this way, Table 7
The results are shown in FIG.

As shown in Table 7, when descaling was carried out according to the descaling method of the present invention, descaling of the hardly descalable stainless steel could be carried out well without salt treatment. .

Before the oxidation-reduction potential of the alkaline permanganate liquid bath does not fall below 350 mV, a voltage of 12 V and an average current density of 700 A / m ² are applied between the plate electrodes spaced apart in the electrolytic cell. By increasing the ratio of Mn ^{7+ in} the liquid bath by performing the electrolytic oxidation by supplying a direct current, the oxidation-reduction potential could be restored to the initial level, and the device could be reused.

[0051]

[Table 5]

[0052]

[Table 6]

[0053]

[Table 7]

[0054]

According to the descaling method of the present invention, as described in claim 1, the descaling material is treated with an alkaline permanganate solution, and then hydrochloric acid or sulfuric acid or a mixture thereof is used as a main component. And treated with a mixed acid containing a water-insoluble carboxylic acid and a surfactant, so that the work environment deteriorates and sludge containing hexavalent chromium is generated, as in the case of conventional salt treatment. It is possible to solve the environmental problems such as the problem of the occurrence of nitrogen oxides (NOx gas) during descaling, as in the case of using a mixed acid of nitric acid and hydrofluoric acid. Without deteriorating the working environment and without increasing the concentration of dissolved nitrogen in the waste liquid, it is difficult to scale
It is extremely easy to descaling the surface of heat-resistant steel, high-speed tool steel, high-alloy steel, etc., and it is possible to prevent the occurrence of surface quality, especially surface roughness and pitting, and to use a descaling material with good surface quality. A very good effect is obtained that it can be obtained.

And, as described in claim 2,
By treating the mixed acid according to claim 1 with a mixed acid containing hydrofluoric acid, it becomes possible to dissolve a hydrofluoric acid-soluble component such as SiO _{2 in} the scale and to further improve the permeability of the mixed acid. This is a remarkably excellent effect.

Further, as described in claim 3, the oxidation-reduction potential can be controlled by treating the mixed acid according to claim 1 or 2 with a mixed acid containing a small amount of nitric acid or a nitric acid compound. At the same time, a remarkably excellent effect that the oxidation-reduction potential can be maintained in the active dissolution potential region is provided.

Further, as described in claim 4, by treating the mixed acid according to claim 1, 2, or 3 with a mixed acid containing a water-soluble carboxylic acid, the dissolved metal ion and the complex salt can be converted. By forming, an extremely excellent effect that it is possible to further improve the life of the pickling liquid is brought about.

Further, as set forth in claim 5, the oxidation-reduction potential of the alkaline permanganate solution bath is set to 35.
By maintaining the voltage at 0 mV or more, it is possible to maintain good descaling property, and it is extremely excellent that it is possible to prevent rough skin and pitting due to deterioration of the alkaline permanganate solution bath. The effect is brought about.

Further, as described in claim 6, Mn ⁶⁺ and Mn ⁶ in an alkaline permanganate solution bath are used.
^By setting the ratio of Mn ⁷⁺ to 75% or more in the component ratio with ⁷⁺ and maintaining the oxidation-reduction potential of the alkaline permanganate liquid bath at 350 mV or more,
A remarkably excellent effect that the descaling property can be maintained satisfactorily and the occurrence of rough skin and pitting due to deterioration of the alkaline permanganate solution bath can be prevented is brought about.

[0060] Furthermore, as described in claim 7, by reproducing processing alkaline permanganate solution bath (electrolytic treatment), with Mn ^{6 +} and Mn ⁷⁺ alkaline permanganate acid solution bath By maintaining the ratio of Mn ⁷⁺ at 75% or more in the component ratio,
It is possible to maintain good descaling properties, prevent the occurrence of rough skin and pitting due to the deterioration of the alkaline permanganate solution bath, and recycle the alkaline permanganate solution to recycle. It is possible to achieve a remarkably excellent effect that it is possible to reduce the processing cost and the waste liquid processing.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of a tendency of a reduction in an oxidation-reduction potential (ORP value) of an alkaline permanganate liquid bath depending on a treatment weight of a descalable material.

FIG. 2 Mn in an alkaline permanganate solution bath
Component Ratio of ⁶⁺ and Mn ⁷⁺ and Redox Potential (ORP)
FIG. 4 is an explanatory diagram showing an example of the relationship with the following.

Claims (7)

[Claims] 1. A method for treating a descalable material with an alkaline permanganate solution, followed by a treatment with a mixed acid mainly containing hydrochloric acid or sulfuric acid or a mixture of both and containing a water-insoluble carboxylic acid and a surfactant. A descaling method characterized by the following. 2. A descaling method comprising treating the mixed acid according to claim 1 with a mixed acid containing hydrofluoric acid. 3. A descaling method comprising treating the mixed acid according to claim 1 or 2 with a mixed acid containing a small amount of nitric acid or a nitric acid compound. 4. A descaling method comprising treating the mixed acid according to claim 1, 2, or 3 with a mixed acid containing a water-soluble carboxylic acid. 5. The descaling method according to claim 1, wherein the oxidation-reduction potential of the alkaline permanganate liquid bath is maintained at 350 mV or more. 6. Mn in an alkaline permanganate liquid bath
^{The descaling} method according to claim 5, wherein in the component ratio of ⁶⁺ and Mn ⁷⁺ , the ratio of Mn ⁷⁺ is 75% or more, and the oxidation-reduction potential of the alkaline permanganate liquid bath is maintained at 350 mV or more. . 7. The alkaline permanganate solution bath is subjected to a regeneration treatment (electrolysis treatment), whereby Mn ⁶⁺ and Mn ⁷⁺ in the alkaline permanganate solution bath have a composition ratio of Mn ⁶⁺ and Mn ^7+.
The ^descaling method according to claim 6, wherein the ratio of ^{n7 +} is maintained at 75% or more.