KR101528052B1 - The Method for Pickling High Cromium Ferrite Stainless Cold Steel Strip using Mixed Acid - Google Patents

Abstract

The present invention relates to a pickling method using a mixed acid solution of 17 to 26% by weight of chromium and a high chromium ferritic stainless steel sheet containing silicon and molybdenum, wherein the annealing temperature (ORP) of the mixed acid solution used in the pickling process, and the concentration of free hydrofluoric acid contained in the mixed acid solution, depending on the kind of the steel component.
The present invention relates to a high chromium ferritic stainless steel sheet which is pickled at an optimum efficiency according to the use and the kind of a steel component so that there is no residual oxide scale on the surface of the stainless steel sheet and the surface gloss is excellent, This excellent stainless steel sheet can be obtained, and further, poor pickling such as pickling and pickling can be alleviated, so that the production cost of the steel sheet can be greatly reduced.

Description

[0001] The present invention relates to a method for pickling high chromium ferritic stainless steel sheets using a mixed acid solution,

According to the present invention, the temperature of the mixed acid solution used in the pickling process, the oxidation-reduction potential (ORP) and the concentration of free hydrofluoric acid contained therein are controlled and the pickling is carried out according to the annealing temperature and the steel species component for the high chromium ferritic stainless steel sheet ≪ / RTI >

Generally, ferritic stainless steels are classified into low-chromium ferritic stainless steels and high-chromium ferritic stainless steels depending on the content of chromium. The case where the chromium content is usually 11 to 14% is referred to as low chromium ferrite stainless steel and the case where the chrome content is 17 to 26% is referred to as high chromium ferrite type stainless steel.

In order to recover the mechanical properties of the ferritic stainless steel after the rolling process, the annealing is performed at a temperature of about 950 to 1100 ° C. When the annealing is carried out, the ferritic stainless steel is oxidized by the components of chromium, iron, Is formed on the outermost surface of the steel sheet and a chromium-depleted layer having a chromium content lower than the average is formed as the chromium is diffused to the outside together with the silicon dioxide oxidation scale as described below at the heat treatment process. Such oxidized scale and chrome-depleted layers deteriorate the appearance quality of the product, and further corrosion starts at the oxidized scale, thereby lowering the corrosion resistance. Therefore, a pickling process is indispensably required for the stainless steel sheet subjected to the annealing heat treatment.

However, the ferritic stainless steel sheet may contain elements such as chromium (Cr), silicon (Si), molybdenum (Mo), copper (Cu), manganese (Mn) The characteristics of the oxidation scale generated during the annealing heat treatment are changed according to the amount of the additive, and accordingly, different pickling methods must be performed depending on the content of the additive element.

That is, in the case of molybdenum (Mo), it is added together with chromium to increase the corrosion resistance of the stainless steel. However, as the content of molybdenum increases, the resistance of the base material and the oxide scale to the acid increases. It is necessary to carry out the pickling.

In addition, when silicon (Si) is added, the silicon dioxide scale is mainly formed at the interface of the base material together with chromium, manganese, and iron scales in annealing annealing of stainless steel. Since the amount and shape change and the silicon dioxide scale does not dissolve in other acids except hydrofluoric acid, it is preferable to conduct the pickling using an acid solution containing hydrofluoric acid.

On the other hand, the ferrite-based stainless steel sheet also has a different oxide scale depending on the content of chromium contained therein. Specifically, in the case of a low-chromium ferrite stainless steel sheet, the scale is thickened during the annealing heat treatment. In the case of a high-chromium ferrite stainless steel sheet And is formed relatively thin.

Further, in order to secure the material of the steel sheet desired by the customer, the annealing can be performed at a temperature higher or lower than the general annealing temperature, that is, the annealing temperature can be lowered in order to obtain a hard steel sheet. In order to obtain a soft steel sheet, The temperature can be increased.

Therefore, even if the same steel grade is used, it can be produced at different annealing temperatures depending on the application. The higher the annealing temperature, the thicker the scale becomes, and the higher the content of chromium and silicon in the scale becomes.

Therefore, the properties of the oxide scale may vary depending on the annealing temperature in addition to the steel species components as described above. Therefore, in order to efficiently conduct pickling, the method of pickling the ferritic stainless steel according to the annealing temperature .

On the other hand, ferritic stainless steel subjected to the annealing heat treatment is subjected to a conventional pickling process by physical descaling such as brush treatment or shot ball blasting, electrolytic descaling using sodium sulfate, sulfuric acid or nitric acid electrolyte, chemical Descaling, and the like, or a combination thereof.

Such a pickling process can be classified into a first stage pretreatment pickling process such as brushing process, shot ball blasting, salt bathing and electrolytic descaling, and a second stage pickling process such as mixed acid immersion. In the finish pickling process, an excellent surface quality is obtained, Conventionally, a mixed acid pickling process has been carried out using a mixed acid solution containing 80 to 180 g / L of nitric acid and 2 to 40 g / L of hydrofluoric acid to improve the corrosion resistance.

In the mixed acid solution, the pH in the silver nitrate pickling bath is lowered to increase the activity of the hydrofluoric acid and to triple oxidize the bivalent iron ions dissolved in the surface of the steel sheet to maintain the redox potential suitable for pickling. However, (NO ₃ -N) in wastewater and wash water. Due to the strengthening of domestic and overseas environmental regulations, the total nitrogen of the discharged effluent is limited and the concentration of NOx in the air discharge facility is limited. There arises a problem that costs are incurred due to the additional installation and operation of the pollution prevention facilities, and the production unit price is remarkably increased.

In order to solve this problem, conventionally, a nitric acid pickling method has been developed in which nitric acid is replaced with hydrochloric acid or sulfuric acid in a pickling process and nitric acid is replaced with insufficient oxidative power by injecting hydrogen peroxide, potassium permanganate, trivalent iron ion and air come.

In this connection, U.S. Patent No. 5908511 discloses that sulfuric acid, hydrofluoric acid, and iron salts are added to hydrogen peroxide regularly, and the composition of humectants, polishes, corrosion inhibitors, Discloses a technique of taking an automatic control scheme as an oxidation-reduction potential (ORP). Through this, CLEANOX352, a pickling solution, has been commercialized and widely used worldwide. Although this method is used for wire and hot-rolled products, the production cost of the product is more than 20% higher than that of existing products, and complex solution composition and management methods are adopted. In addition, it has a relatively slow pickling rate of about 1.5 to 3 g / m < 2 > / min, which is not suitable for the high-speed pickling line in which the pickling must be completed within 10 to 100 seconds.

In addition, EP-A-1040211 and US-A-2000-560982, which are improved patents of the above-mentioned US patents, have proposed a method of increasing the pickling speed by adding copper and chlorine ions to the pickling composition, If the open circuit potential (OCP) formed on the surface is lower than the oxidation-reduction potential of 0.1 V, copper particles may precipitate on the surface of the steel sheet during pickling, thereby discoloring the steel sheet. There is also a risk of pitting corrosion if the pickling solution contains chlorine ions above a certain concentration.

However, when a mixed acid solution of sulfuric acid and hydrofluoric acid is used, the dissolution rate to the scale is low due to the low oxidizing property, and it may cause a blackening phenomenon on the metal surface during the dissolution process. Therefore, an oxidizing agent is added so as to reach the surface potential of the strip having the best acidity, and hydrogen peroxide which does not burden the environment by decomposing the added oxidizing agent is usually used. However, it is not easy to find an appropriate amount of the oxidizing agent to be added. As a result, it is not possible to effectively and quantitatively cope with the problems such as the result of misalignment or over-acidification or the occurrence of blackening of the surface of the steel sheet .

As described above, techniques for securing a mixed acid solution having excellent acidity without containing nitric acid during pickling have been conventionally performed by various methods. However, there have been many problems as described above, and in particular, high chromium- It is more difficult to obtain a proper appearance quality because the difference in the scale of the scale and the dissolution rate of the chrome-depleted layer are relatively larger than those of the other stainless steels depending on the content and the annealing temperature.

An object of the present invention is to provide a pickling method using a mixed acid solution capable of efficiently removing an oxide scale and a chrome-depleted layer even if the characteristics and thickness of the oxide scale vary depending on the annealing temperature and the steel species composition of the high chromium ferritic stainless steel sheet.

According to an embodiment of the present invention, there is provided a pickling method using a mixed acid solution of 17 to 26 wt% chromium and a high chromium ferritic stainless steel sheet containing silicon and molybdenum,

When the contents of chromium, silicon and molybdenum contained in the stainless steel sheet are represented by Cr (wt%), Si (wt%) and Mo (wt%), respectively, the content and the annealing heat treatment temperature satisfy the following formula (1) If so,

The stainless steel sheet may be subjected to a pickling process using a mixed solution of a high chromium ferritic stainless steel sheet containing 80 to 150 g / l sulfuric acid and 5 to 19 g / l free hydrofluoric acid and immersing it in a mixed acid solution having an oxidation- ≪ / RTI >

[Formula (1)

(Annealing heat treatment temperature) > 0 < - > 0 < - >

The redox potential of the mixed acid solution can be maintained by adding hydrogen peroxide to the mixed acid solution.

The hydrogen peroxide remaining in the mixed acid solution can maintain a concentration of 1 to 30 g / l.

The temperature of the mixed acid solution may be 30 to 40 ° C.

The pickling process may be performed for 25 to 90 seconds.

According to another embodiment of the present invention, there is provided a pickling method using a mixed acid solution of 17 to 26 wt% chromium and a high chromium ferritic stainless steel sheet containing silicon and molybdenum,

When the contents of chromium, silicon and molybdenum contained in the stainless steel sheet are represented by Cr (wt%), Si (wt%) and Mo (wt%), respectively, the content and the annealing heat treatment temperature satisfy the following formula If so,

The stainless steel sheet comprises a sans-serif using a mixed solution of a high chromium ferritic stainless steel sheet containing 80 to 150 g / l sulfuric acid and 16 to 30 g / l free hydrofluoric acid and immersing it in a mixed acid solution having an oxidation-reduction potential of 320 mV or higher, ≪ / RTI >

[Expression (2)]

(Annealing heat treatment temperature) < 0 (annealing temperature) &lt; SEP &gt; 0 &lt; SEP &gt;

The redox potential of the mixed acid solution can be maintained by adding hydrogen peroxide to the mixed acid solution.

The temperature of the mixed acid solution may be 40 to 60 캜.

The pickling process may be performed for 25 to 90 seconds.

According to the present invention, by adjusting the temperature of the mixed acid solution used in the pickling process, the oxidation-reduction potential (ORP) and the concentration of hydrofluoric acid contained in the mixed acid solution according to the annealing temperature and the steel species component of the high chromium ferritic stainless steel sheet, It is possible to obtain a stainless steel sheet excellent in surface characteristics free of residual oxide scale on the surface of steel sheet, excellent in surface gloss and free from blackening phenomenon, Furthermore, the production cost of the steel sheet can be greatly reduced as the poor pickling of the pickle and the pickling of the pickle is reduced.

Further, the present invention does not include nitric acid in the mixed acid solution used in the pickling process, so that NOx and nitrate nitrogen are not discharged, air pollution problem does not occur, and burden on the installation of NOx removal facility and denitrification facility is alleviated .

Fig. 1 is an electron micrograph of the surface of a high chromium ferritic stainless steel sheet obtained after a pickling process in Example 1 and Comparative Examples 1 and 2. Fig.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below.

Generally, a high chromium ferritic stainless steel sheet containing 17 to 26% by weight of chromium based on the total weight of the steel sheet is prepared by adding an element such as silicon, molybdenum, or manganese in an amount different from that of the element such as corrosion resistance or deformation resistance do.

In order to recover mechanical properties after the rolling, the high chromium ferritic stainless steel sheet is annealed in a temperature range of approximately 950 to 1100 ° C. At this time, the chromium, iron and manganese contained in the steel sheet may be in the form of oxides And is formed on the outermost surface of the steel sheet, and an oxide layer of silicon dioxide and a chrome-depleted layer are developed directly below the surface.

Since the oxide scale and the chrome-depleted layer lower the surface quality of the steel sheet and significantly lower the corrosion resistance, the oxide scale and chromium depletion present in the high-chromium ferritic stainless steel sheet subjected to the annealing heat treatment Layer is efficiently pickled with a mixed acid solution.

However, the properties and thickness of the oxide scale vary depending on the steel component and the annealing temperature of the high-chromium ferritic stainless steel sheet. Therefore, in the present invention, the pickling process is performed by adjusting the conditions of the mixed acid solution according to the annealing temperature and the steel component , A stainless steel sheet excellent in surface characteristics free of residual oxide scale on the surface of the stainless steel sheet, excellent in surface gloss, and free from blackening, is obtained by carrying out pickling at optimum efficiency even when the use and the kind of the stainless steel sheet are different. can do.

In order to remove the oxide scale and the chrome-depleted layer, the present invention includes a pretreatment pickling step to remove the neutral salts of chromium oxide and iron oxide prior to pickling the high chromium ferritic stainless steel sheet using a mixed acid solution Neutral salt electrolysis, sulfuric acid electrolysis, shot blasting, brushing, and the like.

The neutral salt electrolytic acid may be an electrolytic solution containing sodium sulfate as an electrolyte at a concentration of 100 to 250 g / L, and after the cold-rolled steel sheet is immersed in an electrolytic solution at 50 to 90 ° C, -, and + in the order of at least one time, so that a current of 8 to 30 A / dm ² is applied for 24 to 100 seconds.

The sulfuric acid electrolytic acid may be a sulfuric acid of 50 to 150 g / l or a metal sulfate formed by electrochemically dissolving at least one metal selected from the group consisting of iron, chromium, nickel, copper, manganese, The electrolyte may be used as the electrolytic solution. The cold-rolled steel sheet may be immersed in an electrolytic solution at 30 to 60 ° C, and the surface potential of the steel sheet may be 0 to 30 A / dm &lt; ² &gt; density for 10 to 50 seconds.

In the present invention, most of the oxidized scale existing on the surface of the stainless steel sheet is removed by the pretreatment and pickling process, but a considerable portion remains in the silicon dioxide oxide and the chrome-depleted layer. Further, chromium, molybdenum, silicon, And chromium-depleted layers, and the higher the temperature of the annealing heat treatment performed on the steel sheet, the more silicon dioxide oxide and chrome-depleted layers are developed. Therefore, even if the pickling process by the mixed acid solution It can be difficult to completely remove.

Therefore, in the present invention, in order to effectively remove the oxide scale and the chrome-depleted layer remaining on the surface of the high chromium ferrite stainless steel sheet containing 17 to 26 wt% of chromium and silicon and molybdenum, the chromium, silicon and The content of chromium, silicon, and molybdenum contained in the steel sheet is set to be Cr (wt%), and the content of Cr, Si (wt%) and Mo (wt%), the above-mentioned content and annealing heat treatment temperature are substituted in the following formula. The pH of the mixed acid solution, the temperature of the mixed acid solution, and the oxidation-reduction potential (ORP) of the mixed acid solution are controlled according to the value of the acid solution.

Pickling No.

= 0.09 x Cr (w%) - 0.228 x Mo (w%) - 0.0173 x (Annealing heat treatment temperature)

That is, Is more than 0 and represents a positive value, the stainless steel sheet may be dipped in a mixed acid solution containing 80 to 150 g / l sulfuric acid and 5 to 19 g / l free hydrofluoric acid to conduct the pickling process.

On the other hand, when the content of silicon, chromium, and molybdenum contained in the stainless steel sheet of the present invention is high, the annealing heat treatment temperature is high, or both have high values, The stainless steel sheet may be immersed in a mixed acid solution containing 80 to 150 g / l sulfuric acid and 20 to 30 g / l free hydrofluoric acid to conduct the pickling process.

In the present invention, the hydrofluoric acid contained in the mixed acid solution is dissociated into hydrogen ions and fluoride ions in the solution as shown in the following reaction formula (3). The hydrofluoric acid contained in the mixed acid solution dissociates into hydrogen The equilibrium state is formed by the concentration of ions (H ⁺ ), that is, the acidity.

HF ↔ H ⁺ + F ^- (3)

H ₂ SO ₄ ↔ HSO ₄ ^- + H ⁺ ↔ SO ₄ ^{2 -} + 2H ⁺ (4)

At this time, in the case of hydrofluoric acid, the hydrofluoric acid has an acidity with respect to the oxidation scale in the state of Free HF which is not dissociated, and penetrates the interface between the silicon dioxide oxide and the base material to dissolve the silicon dioxide oxide and Fe, Si ions are combined with FeF _x ^(3-x) , H ₂ SiF ₆ or the like and removed from the surface of the steel sheet.

However, in the present invention, Shows a negative value of less than 0, a large amount of silicon dioxide oxide is present on the surface of the steel sheet or molybdenum is contained in a high content, so that the corrosion resistance of the chrome-depleted layer is increased and the resistance to the mixed acid solution is also greatly increased, In order to effectively remove the silicon dioxide oxide and the chrome-depleted layer, it is preferable to use a mixed acid solution containing a high concentration of free hydrofluoric acid of 20 to 30 g / l.

When the concentration of the free hydrofluoric acid contained in the mixed acid solution is less than 20 g / l under the above-mentioned conditions, the concentration present in the free hydrofluoric acid (HF) is small and the solubility to the silicon dioxide oxide and the chromium- If it exceeds 30 g / l, the erosion speed of the base material is accelerated and the surface of the steel sheet after the acid treatment process may become rough.

On the other hand, in the present invention, The oxide scale existing on the surface of the steel sheet is largely removed by the pre-treatment pickling step, so that only a small amount of residual silicon dioxide oxide is removed, and molybdenum is also contained in a low content, It is preferable to use a mixed acid solution containing 5 to 19 g / l of free hydrofluoric acid since the chrome-depleted layer is not so highly resistant to the mixed acid solution.

In this case, when the concentration of free hydrofluoric acid in the mixed acid solution is less than 5 g / l, the concentration present in the free hydrofluoric acid is too small and the solubility of the remaining silicon dioxide oxide is insufficient, If the amount exceeds 19 g / l, erosion of the base material may occur excessively and the surface of the steel sheet after the pickling process may become rough.

In the present invention, In the case where hydrofluoric acid can remove the silicon dioxide oxide layer on the surface of the steel sheet as described above, the mixed acid solution maintains a certain acidity or higher and the effective free hydrofluoric acid concentration also becomes a certain level or more It needs to be maintained. Therefore, sulfuric acid which provides H ⁺ in a form of free hydrofluoric acid as well as hydrofluoric acid dissociates not only hydrofluoric acid but also dissociated hydrofluoric acid is required at a certain concentration or more. In the present invention, the mixed acid containing sulfuric acid at a concentration of 80 to 150 g / It is preferable to use a solution.

On the other hand, the silicon dioxide oxide present on the surface of the ferritic stainless steel sheet is present both on the grain surface of the ferrite-based crystal and in the grain boundary between grain and grain, and the silicon dioxide oxide of the grain boundary exists deep into the inside of the base material.

Therefore, when treated with a mixed acid solution containing free hydrofluoric acid as described above in order to remove such silicon dioxide, the austenitic stainless steel sheet is high in corrosion resistance of crystals, and is preferentially eroded from grain boundaries, Since the corrosion resistance of the steel is low, there is no difference in the erosion rate between the inside of the crystal and the crystal grains, and therefore, the grain surface and the grain boundary are completely dissolved without selectivity, so dissolution of a substantial part of the base material is inevitable in order to remove all of the silicon dioxide .

When dissolution occurs in the base material, Fe ^{2 +} is eluted from the base material. The eluted Fe ^{2 +} reacts with hydrogen peroxide and is oxidized to Fe ^{3 +} , and then combined with HF to form a complex with FeF _x ^(3-x) And is removed from the steel sheet surface. These series of reactions can be expressed as the following reaction formulas (5) to (8), and the process can smoothly proceed to increase the pickling speed.

Fe ^{0 -} &gt; Fe ^{2 +} + 2e ^- (5)

Fe ^{2 +} + H ₂ O _{2 -} > Fe ^{3 +} +? H + OH ^- (6)

Fe ^{3 +} + 3HF? FeF ₃ + 3H ⁺ (7)

Cu ^{2 +} + 2e ^- ? Cu ⁰ (8)

However, when the insufficient concentration of hydrogen peroxide in the mixed acid solution, and do not support the reaction of the reaction formula (6) made of a Fe ^{2 +} concentration in the surface of the steel sheet increases locally is in the left direction reaction of the reaction formula (5) it is predominantly . In this case, as in the reaction formula (8), Cu or the like present as an additive or an impurity in Fe and stainless steel is re-precipitated on the surface of the steel sheet, causing a black phenomenon in which the surface of the steel sheet is changed to black. Therefore, in the present invention, it is preferable that the reaction of the reaction formula (6) can be carried out by keeping the oxidation-reduction potential of the solution at a constant level by always putting a certain amount of hydrogen peroxide.

Therefore, in the present invention, Has a negative value of less than 0, the content of chromium, molybdenum, and silicon contained in the stainless steel sheet is high, so that the silicon dioxide oxide layer develops when the annealing temperature is high even when the resistance to the acid is high or the corrosion resistance is low, It is sufficient to add hydrogen peroxide to the mixed acid solution so that the redox potential of the solution is maintained at 320 mV or more because the amount of the ferrous ions eluted from the base material to the mixed acid solution is not so large.

However, in the present invention, Is a positive value exceeding 0, it is preferable to add hydrogen peroxide to the mixed acid solution and maintain the oxidation-reduction potential at 550 mV or higher, since the amount of the ferrous ion eluted from the base material to the mixed acid solution is equivalent, It is preferable that the hydrogen peroxide is added in such a manner that the concentration of residual hydrogen peroxide in the solution is maintained in the range of 1 to 30 g / l after the three kinds of ferrous ions eluted from the mixed acid solution are all oxidized.

Further, in the present invention, the higher the content of chromium, molybdenum, and silicon, the higher the annealing temperature, and the more severe the pickling conditions, the more desirable is Pickling. Has a negative value of less than 0, it is preferable to increase the pickling rate using a mixed acid solution at 40 to 60 ° C in the pickling step. Is a positive value exceeding 0, a mixed acid solution having a temperature of 30 to 40 占 폚 in the pickling step is sufficient to remove trace amounts of residual silicon dioxide and chrome-depleted layers.

In the present invention, the time for performing the pickling process, that is, the time for immersing the stainless steel plate in the mixed acid solution is not particularly limited and may be varied depending on the operating conditions. However, for 25 to 90 seconds, It is preferable to sufficiently remove the layer.

Example

Hereinafter, the present invention will be described more specifically by way of specific examples. The following examples are provided to aid understanding of the present invention, and the scope of the present invention is not limited thereto.

[Examples 1 to 8 and Comparative Examples 1 to 14]

The high chromium ferritic stainless steel sheet having the composition shown in the following Table 1 was annealed at the annealing heat treatment temperature shown in the following Table 1 for 1 minute and then subjected to a heat treatment at a current density of 15 A / dm ² in a 150 g / L solution of sodium sulfate at 90 캜 (+), (-), and (+) for 30 seconds on the surface of the steel sheet and then electricity of 15 A / dm ² in 70 g / L solution of sulfuric acid at 50 ° C., ) Was applied to the surface of the steel sheet for 30 seconds in order, and the pretreatment and pickling process was carried out. Then, the contents of chromium, silicon and molybdenum contained in the steel sheet were respectively expressed by Cr (wt%), Si (wt%) and Si The results are shown in Table 1 below. When the value is a negative value, Method 1 includes immersing in a mixed acid solution of 55 占 폚 for 30 seconds, the solution containing 150 g / L of sulfuric acid and 30 g / L of free hydrofluoric acid, maintaining the ORP at 320 mV or more without residual hydrogen peroxide, Were performed. When the value is a positive value, Method 2 contains 80 g / L of sulfuric acid and 7 g / L of free hydrofluoric acid, the concentration of residual hydrogen peroxide is 3 g / L, the ORP is maintained at 550 mV or more, For 30 seconds to conduct a pickling process.

The state of the finally obtained steel sheet after the pickling process is shown in Table 1 below. An electron microscope photograph of the surface of the steel sheet of Example 1 and Comparative Examples 1 and 2 is shown in Figs. 1 (a) to 1 ).

Pickling No.

(Annealing heat treatment temperature) = 19.5 - 0.510 x Si (w%) - 0.069 x Cr (w%) - 0.228 x Mo (w%) - 0.0173 x

Cr (w%) Si (w%) Mo (w%) Annealing heat treatment
Temperature (℃) Pickling
No. Mixed mountain
Way Pickle
surface Example 1 17.0 0.16 0.01 1020 0.60 Method 2 normal Example 2 17.0 0.16 0.01 1040 0.25 Method 2 normal Comparative Example 1 17.0 0.16 0.01 1060 -0.09 Method 2 Misanthus tax Comparative Example 2 17.0 0.16 0.01 1020 0.60 Method 1 And pickles Example 3 18.5 0.18 1.95 1050 -0.48 Method 1 normal Comparative Example 3 18.5 0.18 1.95 1010 0.21 Method 1 And pickles Comparative Example 4 18.5 0.18 1.95 1050 -0.48 Method 2 Misanthus tax Example 4 19.5 0.4 0.15 1070 -0.59 Method 1 normal Comparative Example 5 19.5 0.4 0.15 1020 0.27 Method 1 And pickles Comparative Example 6 19.5 0.4 0.15 1070 -0.59 Method 2 Misanthus tax Example 5 18.0 0.32 0.02 1055 -0.16 Method 1 normal Comparative Example 7 18.0 0.32 0.02 1020 0.44 Method 1 And pickles Comparative Example 8 18.0 0.32 0.02 1055 -0.16 Method 2 Misanthus tax Example 6 18.0 0.1 1.06 1045 -0.11 Method 1 normal Comparative Example 9 18.0 0.1 1.06 1010 0.49 Method 1 And pickles Comparative Example 10 18.0 0.1 1.06 1045 -0.11 Method 2 Misanthus tax Example 7 17.5 0.1 0.45 1040 0.15 Method 2 normal Comparative Example 11 17.5 0.1 0.45 1040 0.15 Method 1 And pickles Comparative Example 12 17.5 0.1 0.45 1070 -0.37 Method 2 Misanthus tax Example 8 21.0 0.14 0.01 1010 0.50 Method 2 normal Comparative Example 13 21.0 0.14 0.01 1010 0.50 Method 1 And pickles Comparative Example 14 21.0 0.14 0.01 1050 -0.19 Method 2 Misanthus tax

As shown in Table 1, in the case of Examples 1, 2, 7 and 8, Is larger than 0, and when the pickling process is carried out by the method 2, it can be seen that the normal pickling is carried out. Particularly in FIG. 1 (a), the shape of the normal pickling surface can be seen in accordance with the embodiment 1 .

On the other hand, annealing was performed under the same conditions as in Examples 1, 7 and 8, but in Comparative Examples 2, 11 and 13 in which the pickling method was performed differently, over-picking occurred. Particularly in FIG. 1 (c) It can be seen that over-pickling occurs according to Comparative Example 2 and surface erosion occurs.

In addition, the steel composition was the same as those of Examples 1, 7 and 8, but the annealing heat treatment temperature was higher. Comparative Example 1, Comparative Example 1, Comparative Example 1, Comparative Example 1, Comparative Example 1, Comparative Example 1, Comparative Example 1, Comparative Example 1, Comparative Example 1, Comparative Example 1, and Comparative Example 2 were conducted in the same manner as in Examples 1, It can be seen that there is a miscarriage on the surface.

In Examples 3 to 6, Was calculated to be smaller than 0, and when the pickling process was carried out using the method 1, the normal surface appeared on the steel sheet, but the annealing was carried out under the same conditions. However, in Comparative Examples 4, 6, 8 and 10 Is a miscarriage.

On the other hand, in Comparative Examples 3, 5, 7 and 9 in which the steel compositions were the same as those of Examples 3 to 6 but the annealing heat treatment temperature was lower and Pickling No. was larger than 0, As a result of pickling process, over - picking occurred.

That is, when the content of chromium, silicon and molybdenum contained in the high-chromium ferritic stainless steel sheet and the annealing heat treatment temperature were substituted in the above equation, In the case where the pickling process is carried out by using the method 2 in the case of showing a positive value and when the pickling process is carried out by using the method 2 in the case of showing a negative value, the remaining oxidized scale and the chrome-depleted layer are all removed, Pickling No. 1, And the method 1 is applied when a positive value is indicated, it can be seen that there is a misrecognition or overpayment.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be obvious to those of ordinary skill in the art.

Claims (8)

In a pickling method using a mixed acid solution of 17 to 26 wt% chromium and a high chromium ferritic stainless steel sheet containing silicon and molybdenum,
When the contents of chromium, silicon and molybdenum contained in the stainless steel sheet are represented by Cr (wt%), Si (wt%) and Mo (wt%), respectively, the content and the annealing heat treatment temperature satisfy the following formula (1) If so,
The stainless steel sheet is sansilized with a mixed solution of a high chromium ferritic stainless steel sheet containing 80 to 150 g / l of sulfuric acid and 5 to 19 g / l of free hydrofluoric acid and immersing it in a mixed acid solution having an oxidation-reduction potential of 550 mV or more, Way.
[Formula (1)
(Annealing heat treatment temperature) > 0 &lt; - &gt; 0 &lt; - &gt;
In a pickling method using a mixed acid solution of 17 to 26 wt% chromium and a high chromium ferritic stainless steel sheet containing silicon and molybdenum,
When the contents of chromium, silicon and molybdenum contained in the stainless steel sheet are represented by Cr (wt%), Si (wt%) and Mo (wt%), respectively, the content and the annealing heat treatment temperature satisfy the following formula If so,
The stainless steel sheet comprises a sans-serif using a mixed solution of a high chromium ferritic stainless steel sheet containing 80 to 150 g / l sulfuric acid and 16 to 30 g / l free hydrofluoric acid and immersing it in a mixed acid solution having an oxidation-reduction potential of 320 mV or higher, Way.
[Expression (2)]
(Annealing heat treatment temperature) < 0 (annealing temperature) &lt; SEP &gt; 0 &lt; SEP &gt;
The pickling method according to claim 1, wherein the redox potential of the mixed acid solution is maintained by adding hydrogen peroxide to the mixed acid solution.
4. The pickling method according to claim 3, wherein the hydrogen peroxide remaining in the mixed acid solution is maintained at a concentration of 1 to 30 g / l by using a mixed acid solution of a high-chromium ferritic stainless steel plate.
3. The pickling method according to claim 2, wherein the redox potential of the mixed acid solution is maintained by adding hydrogen peroxide to the mixed acid solution.
The pickling method according to claim 1, wherein the mixed acid solution has a temperature of 30 to 40 ° C.
3. The pickling method according to claim 2, wherein the mixed acid solution has a temperature of 40 to 60 DEG C, using a mixed acid solution of a high chromium ferritic stainless steel sheet.
The pickling method according to claim 1 or 2, wherein the pickling step is carried out for 25 to 90 seconds using a mixed acid solution of a high chromium ferritic stainless steel sheet.

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