KR20190072278A - High chromium ferritic stainless steel excellent in pickling property and its pickling method - Google Patents

Abstract

Disclosed are a ferritic stainless steel and a pickling method thereof, which can obtain a scale thickness convenient for pickling by adjusting the thickness of Mn oxides of a surface layer scale and the thickness of Si oxides of the inside of a high Cr ferritic stainless steel having Si and Nb. The high Cr ferritic stainless steel with a superior pickling property according to an embodiment of the present invention comprises, by wt%: 0.02% or less of C; 0.3-0.6% of Si; 0.1-0.5% of Mn; 0.03% or less of P; 0.005% or less of S; 17.0-26.0% of Cr; 0.6% or less of Ni; 0.1-0.6% of Nb; 0.1% or less of Sn; 0.05% or less of N; and the remaining consisting of Fe and inevitable impurities, and satisfies the following formula (1). (1) 0.115 <= 0.123 - 0.0108*Sn + 0.0151*Si - 0.0147*Mn + 0.0089*Ni - 0.0105*Sn*Si <= 0.130

Description

FIELD OF THE INVENTION [0001] The present invention relates to a high Cr ferritic stainless steel having excellent acid pickling properties and a pickling method therefor. BACKGROUND ART [0002] HIGH CHROMIUM FERRITIC STAINLESS STEEL EXCELLENT IN PICKLING PROPERTY AND ITS PICKLING METHOD [

The present invention relates to a ferritic stainless steel excellent in acidity and a method for pickling the ferritic stainless steel. More particularly, the present invention relates to a ferritic stainless steel excellent in acidity, The present invention relates to a ferritic stainless steel and a method for pickling the ferritic stainless steel, which can ensure a scale thickness with ease of pickling by adjusting the inner Si oxide thickness.

Generally, ferritic stainless steels are classified into low Cr ferritic stainless steels and high Cr ferritic stainless steels depending on the Cr content. A case where the Cr content is in the range of 11 to 14 wt% is called low Cr ferritic stainless steel, and a case where the Cr content is 17 to 26 wt% is called high Cr ferritic stainless steel.

Since the scale characteristics formed during the annealing heat treatment vary depending on the Cr content, the pickling method according to the Cr content must be performed differently. Generally, in the case of low-Cr ferritic stainless steel, the scale is thickened during the annealing heat treatment, and in the case of high Cr ferritic stainless steel, the scale thickness is relatively thinner than that of the low-Cr ferritic stainless steel during the annealing heat treatment.

In addition, there is a difference in the heat treatment temperature at the time of annealing depending on the characteristics of each steel type. The higher the annealing temperature, the larger the scale is formed, and the Cr content is also increased. Such a scale not only deteriorates the appearance quality of the product but also may cause corrosion from the oxidation scale to deteriorate the corrosion resistance. Therefore, it is necessary to remove the scale formed on the surface through the pickling process.

Si and Nb are elements added to ferritic stainless steels for exhaust systems used in high-temperature applications as elements that increase the high-temperature oxidation characteristics and high-temperature strength, respectively. However, when such an element is added, there is a problem that the acidity is remarkably lowered.

In order to improve electrolytic pickling ability and acid precipitation pickling resistance of a high-Cr ferritic stainless steel added with Si and Nb, it is necessary to adjust the Mn oxide thickness and the inner Si oxide thickness of the surface layer scale, Ferritic stainless steel and a pickling method thereof.

The high Cr ferritic stainless steel according to one embodiment of the present invention is characterized by containing 0.02% or less of C, 0.3 to 0.6% of Si, 0.1 to 0.5% of Mn, 0.03% or less of P, And a balance of Fe and unavoidable impurities, wherein the S content is 0.005% or less, Cr is 17.0 to 26.0%, Ni is 0.6% or less, Nb is 0.1 to 0.6%, Sn is 0.1% 1).

(One) 0.115? 0.123 - 0.0108 * Sn + 0.0151 * Si - 0.0147 * Mn + 0.0089 * Ni - 0.0105 * Sn * Si? 0.130

Here, Sn, Si, Mn, and Ni mean the content (weight%) of each element.

According to an embodiment of the present invention, the stainless steel may further include 0.5% or less of Cu and 0.01% or less of Al.

A pickling method for a high-Cr ferritic stainless steel according to an embodiment of the present invention is a pickling method for a high-Cr ferritic stainless steel which comprises 0.02% or less of C, 0.3 to 0.6% of Si, 0.1 to 0.5% of Mn, 0.03% or less of P, The cold-rolled steel sheet containing 0.005% or less of Cr, 17.0 to 26.0% of Cr, 0.6% or less of Ni, 0.1 to 0.6% of Nb, 0.1% or less of Sn and 0.05% or less of N and the remaining Fe and unavoidable impurities step; Electrolytically pickling the cold-rolled annealed material; And a mixed solution containing sulfuric acid and hydrofluoric acid, wherein the annealing heat treatment is performed at a temperature of 1,030 to 1,070 ° C. within 3 minutes, and a scale thickness (μm) of the cold-rolled annealed material is expressed by the following formula Satisfies.

(One) 0.115? 0.123 - 0.0108 * Sn + 0.0151 * Si - 0.0147 * Mn + 0.0089 * Ni - 0.0105 * Sn * Si? 0.130

Here, Sn, Si, Mn, and Ni mean the content (weight%) of each element.

According to an embodiment of the present invention, the step of electrolytic pickling comprises neutral salt electrolytic pickling and sulfuric acid electrolytic pickling, wherein the applied current of the neutral salt electrolytic bath and the sulfuric electrolytic bath is 9 to 10 A / dm ² , The time can be within 90 seconds.

According to an embodiment of the present invention, the temperature of the neutral salt electrolyzer may be 70 to 80 ° C, and the temperature of the sulfate bath may be 40 to 50 ° C.

According to an embodiment of the present invention, the neutral salt concentration of the neutral salt electrolytic acid is 180 to 220 g / L, and the sulfuric acid concentration of the sulfuric acid electrolytic acid may be 60 to 100 g / L.

According to an embodiment of the present invention, the redox potential (ORP) of the mixed acid solution may be 370 mV or more.

Also, according to an embodiment of the present invention, the temperature of the mixed acid solution may be 45 to 55 ° C.

According to an embodiment of the present invention, the sulfuric acid concentration of the mixed acid solution may be 80 to 150 g / L, and the hydrofluoric acid concentration of the mixed acid solution may be 20 to 30 g / L.

According to the embodiment of the present invention, the scale thickness can be adjusted to a thickness that facilitates pickling by adjusting the content of Mn, Si, Ni, and Sn alloy components.

Further, by optimizing electrolytic pickling and conic pickling conditions, excellent surface quality can be ensured after pickling.

FIG. 1 is a graph showing an optimum scale thickness range according to changes in Mn content and Si content.
2 is a photograph showing a scale sectional shape of Comparative Example 5. Fig.
3 is a graph showing an analysis of the alloy component according to the scale depth d in FIG.
4 is a photograph showing a scale sectional shape of Comparative Example 6. Fig.
FIG. 5 is a graph showing an analysis of alloy components according to the scale depth (d) in FIG.
6 is a graph showing changes in current with time after application of 1.5 V to a gamma electrode in an 80 g / L sulfuric acid solution of a cold-rolled annealed steel sheet of Comparative Example 5 and Comparative Example 6. Fig.
FIGS. 7 and 8 are electron micrographs of a scale surface layer portion of Comparative Example 5 and Comparative Example 6 after application of 1.5 V to a gamma-ray electrode in a sulfuric acid solution of 80 g / L at 50 ° C for 120 seconds.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided to fully convey the spirit of the present invention to a person having ordinary skill in the art to which the present invention belongs. The present invention is not limited to the embodiments shown herein but may be embodied in other forms. For the sake of clarity, the drawings are not drawn to scale, and the size of the elements may be slightly exaggerated to facilitate understanding.

Also, when an element is referred to as "comprising ", it means that it can include other elements as well, without departing from the other elements unless specifically stated otherwise.

The singular forms &quot; a &quot; include plural referents unless the context clearly dictates otherwise.

Generally, in producing a stainless steel cold-rolled steel sheet, in order to obtain an excellent surface quality by removing an oxide scale formed on a steel sheet and to improve the corrosion resistance of the steel sheet, physical descaling such as brushing or short ball blasting, Electrolytic descaling using nitric acid electrolytes, and chemical descaling by salt bathing or mixed acid treatment. Such processes are collectively referred to as a "pickling process".

In this pickling process, a two-step mixed impregnation process such as electrolytic descaling and chemical descaling such as electrolysis descaling is distinguished.

In the first step electrolytic pickling process, the dissolution reaction is delayed in the electrolytic pickling process when the thickness of the Mn and Cr composite oxide in the surface layer is large. On the contrary, if the Si oxide is formed thickly in the electrolytic pickling process, the dissolution reaction is delayed in the second step mixed pickling process. Therefore, it is necessary to control the thickness of the surface layer Mn oxide and the thickness of the Si oxide to facilitate the pickling.

As described above, ferritic stainless steels are required to have high-temperature oxidation resistance or high-temperature strength depending on the application, and Si and Nb are added in order to improve them. The pickling problem of the cold- Occurs.

In the present invention, in order to improve the acidity of high Cr ferritic stainless steels containing 17 wt% or more of Cr, the contents of Si, Mn, Ni and Sn were controlled to optimize the scale thickness.

As a result of analyzing the scale of GDS (Glow Discharge Spectroscope) on the cold - rolled steel sheet subjected to the cold annealing annealing, the effect of alloying elements on the scale thickness could be analyzed. Of the alloying elements, Si, Mn, Ni, and Sn have an effect on the scale thickness, and Si and Sn have an interplay effect. Si and Ni increase the scale thickness, and Mn and Sn decrease the scale thickness. Also, Si and Sn interact to reduce the scale thickness.

When the influence of the alloying element which influences the scale thickness of the high Cr ferritic stainless steel is quantified, the range of the scale thickness (탆) can be expressed by the following equation (1).

(One) 0.115? 0.123 - 0.0108 * Sn + 0.0151 * Si - 0.0147 * Mn + 0.0089 * Ni - 0.0105 * Sn * Si? 0.130

When the scale thickness of the high Cr ferritic stainless steel to which Si and Nb are added is in the range of 0.115 to 0.130 mu m, the pickling performance can be improved.

The high Cr ferritic stainless steel according to one embodiment of the present invention is characterized by containing 0.02% or less of C, 0.3 to 0.6% of Si, 0.1 to 0.5% of Mn, 0.03% or less of P, S: 0.005% or less, Cr: 17.0 to 26.0%, Ni: 0.6% or less, Nb: 0.1-0.6%, Sn: 0.1% or less, N: 0.05% or less and Fe and unavoidable impurities.

Hereinafter, the reasons for limiting the numerical values of the alloy element content in the examples of the present invention will be described. Unless otherwise stated, the unit is wt%.

The content of C is 0.02% or less.

C is an element that greatly affects the strength of the steel. When the content is excessive, the strength of the steel is excessively increased to deteriorate the ductility, which is limited to 0.02% or less.

The content of Si is 0.3 to 0.6%.

Si is an element added for deoxidation of molten steel during steelmaking and stabilization of ferrite. In the present invention, at least 0.3% of Si is added to improve oxidation resistance and corrosion resistance at high temperature. However, in order to improve pickling performance, it is preferable to limit the effect to 0.6% or less in consideration of the effect on the scale thickness derived above.

The content of Mn is 0.1 to 0.5%.

Mn is an element effective for improving oxidation resistance. In the present invention, 0.1% or more is added, and more preferably, 0.2% or more is added. However, when the Mn content exceeds 0.5% in the Si content of 0.6% or less, pickling resistance is significantly lowered, so the upper limit is limited to 0.5%.

The content of P is 0.03% or less.

P is an impurity inevitably contained in the steel, and is an element that causes intergranular corrosion at the time of pickling or hinders hot workability. Therefore, it is preferable to control the content as low as possible. In the present invention, the upper limit of the P content is controlled to 0.03% or less.

The content of S is 0.005% or less.

S is an impurity inevitably contained in steel, and is an element that is segregated in grain boundaries and is a main cause of inhibiting hot workability. Therefore, it is preferable to control the content to be as low as possible. In the present invention, the upper limit of the S content is controlled to 0.005% or less.

The content of Cr is 17.0 to 26.0%.

Cr is an element effective for improving the corrosion resistance of steel, and is limited to high Cr ferritic stainless steel in the range of 17.0 to 26.0% in the present invention.

The content of Ni is 0.6% or less.

In ferritic stainless steels, Ni can be treated as an impurity, but is partially incorporated in the scrap melting process. The Ni upper limit is limited to 0.6%, and the Ni content partially contained therein controls the scale thickness according to the above formula (1).

The content of Nb is 0.1 to 0.6%.

Nb is preferentially combined with C and N to form a precipitate which suppresses deterioration of corrosion resistance. When the amount of Nb is less than 0.1%, there is a problem that the high temperature strength of the material is lowered because Nb is small in the material, The oxide layer becomes thick at the interface when annealed, and the acidity is deteriorated.

The content of Sn is 0.1% or less.

Sn suppresses Si oxide growth when added and improves corrosion resistance in an acidic atmosphere. However, if the content is excessive, the hot workability is deteriorated and the content is limited to 0.1% or less.

The content of N is 0.05% or less.

N is an element that accelerates recrystallization by precipitation of austenite during hot rolling. However, when the content is excessive, the ductility of steel is deteriorated, and it is limited to 0.05% or less.

In addition, according to an embodiment of the present invention, it may further include not more than 0.5% of Cu and not more than 0.01% of Al.

The content of Cu is 0.5% or less.

Cu can be added as an element for improving corrosion resistance in order to improve corrosion resistance in an acidic atmosphere. However, when Cu is added excessively, there is a risk of lowering the formal potential in the chloride atmosphere, which is limited to 0.5% or less.

The content of Al is 0.01% or less.

Al is a strong deoxidizer, which serves to lower the content of oxygen in the molten steel, but excessive addition causes a decrease in ductility at room temperature, so the upper limit is set to 0.01%, and it may not be contained.

FIG. 1 is a graph showing an optimum scale thickness range according to changes in Mn content and Si content.

FIG. 1 shows an optimum scale thickness range (white area) in which acidity is improved depending on the content of Mn and Si after fixing the Sn content to 0.06% and the Ni content to 0.5%. In order to secure good acidity in high-Cr ferritic stainless steels with Si and Nb added, the Mn content should be low when the Si content is low, and the Mn content should be high when the Si content is high. If the Mn content exceeds 0.5% in the Si content of 0.6% or less, a remarkable decrease in pickling resistance can be expected. This is related to the range limitation of Si and Mn among the alloying elements of the present invention.

When the optimum scale thickness range within the range of the above-described alloy element component satisfies the above formula (1), excellent pickling performance can be exhibited in the pickling process of the cold-rolled and annealed steel sheet to be described later.

Next, a pickling method of a high Cr ferritic stainless steel according to an embodiment of the present invention will be described.

A pickling method for a high-Cr ferritic stainless steel according to an embodiment of the present invention is a pickling method for a high-Cr ferritic stainless steel which comprises 0.02% or less of C, 0.3 to 0.6% of Si, 0.1 to 0.5% of Mn, 0.03% or less of P, , The Fe and the unavoidable impurities are contained in an amount of 0.005 to 0.005%, 17.0 to 26.0% of Cr, 0.6% or less of Ni, 0.1 to 0.6% of Nb, 0.01 to 0.1% ; Electrolytically pickling the cold-rolled annealed material; And a mixed solution containing sulfuric acid and hydrofluoric acid, wherein the annealing heat treatment is performed at a temperature of 1,030 to 1,070 ° C. within 3 minutes, and a scale thickness (μm) of the cold-rolled annealed material is expressed by the following formula Satisfies.

(One) 0.115? 0.123 - 0.0108 * Sn + 0.0151 * Si - 0.0147 * Mn + 0.0089 * Ni - 0.0105 * Sn * Si? 0.130

The reason for limiting the numerical value of the alloy element content is as described above.

The alloying element component according to the present invention and the cold-rolled steel sheet satisfying the formula (1) can be heat treated at a temperature of 1,030 to 1,070 ° C for 3 minutes or less to form a scale having a thickness of 0.115 to 0.130 μm on the surface of the steel sheet.

The cold-rolled annealed material is subjected to a pickling process in an electrolytic pickling step and a mixed pickling step, and the electrolytic pickling step may include neutral salt electrolytic pickling and sulfuric acid electrolytic pickling.

The applied current of the neutral salt electrolytic cell and the sulfuric acid electrolytic cell in the electrolytic pickling step is 9 to 10 A / dm ² , and the current application time can be 90 seconds or less. When the applied electric current is less than 9 A / dm ^2, surface potential capable of dissolving the annealing scale is not formed, so that miscarriage can occur. When the applied current exceeds 10 A / dm ² , surface erosion due to pickling may occur. To 10 A / dm &lt; ^{2 &} gt ;.

The neutral salt concentration of the neutral salt electrolytic pickling may be 180 to 220 g / L, and the sulfuric acid concentration of the sulfuric acid electrolytic pickling may be 60 to 100 g / L. The neutral salt electrolytic bath temperature is preferably 70 to 80 ° C, and the sulfuric acid electrolytic bath temperature is preferably 40 to 50 ° C.

Since the Mn, Cr and Fe oxide layers are removed and only the Si oxide layer is left on the surface of the high Cr ferrite cold-rolled annealed sheet subjected to neutral salt electrolytic pickling and sulfuric acid electrolytic pickling, after the electrolytic pickling, the mixed acid solution containing sulfuric acid and hydrofluoric acid is immersed .

The sulfuric acid concentration in the mixed acid solution may be 80 to 150 g / L and the hydrofluoric acid concentration may be 20 to 30 g / L. The hydrofluoric acid dissolves the Si oxide and bonds it in the form of H ₂ SiF ₆ or the like to remove the Si oxide from the surface of the steel sheet. If the concentration of hydrofluoric acid is less than 20 g / L, the dissolution of the Si oxide layer may be insufficient, which may cause problems on the surface of the steel sheet. If the hydrofluoric acid concentration exceeds 30 g / L, It can be rough. The sulfuric acid concentration is preferably adjusted to a range of 80 to 150 g / L in order to maintain the acidity of hydrofluoric acid in the mixed acid solution for removing the Si oxide layer.

In addition, the redox potential (ORP) of the mixed acid solution is preferably 370 mV or more, and the mixed acid solution is preferably maintained at 45 to 55 ° C.

Hereinafter, preferred embodiments of the present invention will be described in detail.

Example

The slabs having the compositions shown in the following Table 1 were produced, hot rolled and hot-rolled and annealed in the slabs, cold-rolled, and cold-annealed at 1,050 ° C for 2 minutes and 30 seconds to obtain 2.0 mm cold rolled annealed steel sheets. The scale thickness of the cold-rolled annealed steel sheet was measured by GDS (Glow Discharge Spectroscope) and the depth to the maximum concentration of Si oxide existing therein. Therefore, the actual scale thickness may be thicker than the thickness shown in Table 1. [

division Composition (% by weight) scale
thickness
(탆) Sn Si Mn Ni C P S Cr Cu Al Nb N Comparative Example 1 0.061 0.35 0.19 0.098 0.009 0.023 <0.003 19.3 0.44 0.003 0.43 0.0098 0.1025 Comparative Example 2 0.059 0.37 0.50 0.110 0.010 0.024 <0.003 19.2 0.46 0.004 0.47 0.0094 0.0846 Comparative Example 3 0.061 0.36 0.49 0.51 0.010 0.025 <0.003 19.3 0.46 0.005 0.43 0.0096 0.0979 Comparative Example 4 0 0.35 0.49 0.098 0.008 0.023 <0.003 19.3 0.45 0.004 0.46 0.0100 0.0856 Comparative Example 5 0 0.56 0.18 0.100 0.008 0.021 <0.003 19.5 0.45 0.005 0.42 0.0110 0.1897 Comparative Example 6 0.059 0.61 0.50 0.107 0.010 0.025 <0.003 19.2 0.46 0.004 0.43 0.0098 0.1003 Comparative Example 7 0 0.58 0.49 0.101 0.010 0.024 <0.003 19.4 0.46 0.004 0.46 0.0092 0.1113 Comparative Example 8 0 0.57 0.48 0.50 0.009 0.022 <0.003 19.2 0.45 0.005 0.48 0.011 0.1506 Comparative Example 9 0 0.59 0.18 0.51 0.010 0.021 <0.003 19.4 0.45 0.004 0.45 0.012 0.186 Comparative Example 10 0.059 0.36 0.19 0.48 0.009 0.023 <0.003 19.4 0.45 0.004 0.45 0.011 0.1454 Inventory 1 0 0.35 0.17 0.49 0.009 0.022 <0.003 19.3 0.44 0.004 0.44 0.0100 0.1161 Inventory 2 0.056 0.56 0.18 0.12 0.011 0.021 <0.003 19.4 0.46 0.005 0.46 0.011 0.115 Inventory 3 0 0.36 0.19 0.098 0.008 0.021 <0.003 19.5 0.44 0.004 0.43 0.010 0.124 Honorable 4 0 0.36 0.50 0.48 0.009 0.021 <0.003 19.4 0.46 0.004 0.47 0.011 0.1071 Inventory 5 0.060 0.58 0.17 0.50 0.010 0.023 <0.003 19.4 0.45 0.003 0.47 0.012 0.1226 Inventory 6 0.058 0.57 0.50 0.51 0.009 0.023 <0.003 19.3 0.45 0.005 0.45 0.011 0.1289

In Table 1, Comparative Examples 1 to 10 are grades out of the scale thickness range according to the formula (1) of the present invention, and Examples 1 to 6 are grades in which the scale thickness corresponds to the range of the present invention.

2 is a photograph showing a scale sectional shape of Comparative Example 5. Fig. Referring to FIG. 2, it can be seen that the outer layer scale and the inner layer scale are formed in the direction of the scale depth (d). Unlike the shape of the outer layer scale, the inner layer scale has a spherical shape.

3 is a graph showing an analysis of the alloy component according to the scale depth d in FIG. Referring to FIG. 3, it can be seen that the main component of the outer layer scale is Cr oxide, and Mn and Fe oxide are partially used. It can also be seen that the Si oxide as the inner layer scale is developed as compared with the outer layer scale. In Table 1, it can be seen that the Mn content is as low as 0.18% in Table 1. When the Mn content is low, the development of the composite oxides of Mn and Cr is delayed in the surface layer, but the development of the inner Si oxide is promoted. As a result, the scale thickness was measured to be 0.1897 ㎛, and it could be expected that pickling in the step of mixed impregnation with thick Si oxide was difficult.

4 is a photograph showing a scale sectional shape of Comparative Example 6. Fig. Referring to FIG. 4, Comparative Example 6 is composed of outer layer scale and inner layer scale, but unlike Comparative Example 5, the thickness of the outer layer scale is thinned and the inner layer scale is inhibited from development. Also, it was found that the scale thickness was decreased as a whole.

FIG. 5 is a graph showing an analysis of alloy components according to the scale depth (d) in FIG. Referring to Fig. 5, it can be seen that the major components of the outer layer scale are Cr and Mn oxides, and Fe oxide is also substantially solved. The inner layer scale was made of Si oxide. Mn oxide was developed in the surface layer, and growth of internal Si oxide was suppressed. In Table 1, it can be seen that the Mn content of Comparative Example 6 is as high as 0.50%, and when the Mn content is high, the overall scale thickness tends to decrease. The scale thickness was measured to be 0.1003 ㎛ and the development of Mn oxides could predict the difficulty in electrolytic pickling.

Then, the cold-rolled annealed specimens shown in Table 1 were subjected to one-step neutral salt electrolytic pickling, sulfuric acid electrolytic pickling, and two-step mixed acid pickling pickling. The neutral salt electrolytic acid was applied at a rate of 0.1 A / cm _{2 in} a Na ₂ SO ₄ solution of 200 g / L at 75 ° C. Sulfuric acid electrolytic acid was applied at a rate of 0.1 A / cm _{2 in} a H ₂ SO ₄ solution of 100 g / L at 50 ° C. The mixed acid immersion was carried out at 55 캜 for 180 seconds in a mixed solution of 100 g / L of sulfuric acid and 28 g / L of hydrofluoric acid.

6 is a graph showing changes in current with time after application of 1.5 V to a calomel electrode in an 80 g / L sulfuric acid solution of a cold-rolled annealed steel sheet of Comparative Example 5 and Comparative Example 6. Fig.

Referring to FIG. 6, Comparative Example 5 having a low Mn content shows a high current density of 10,000 μA / cm 2. On the other hand, Comparative Example 6, which has a high Mn content, shows a very low current density. That is, when the Mn content is high, it is found that the oxides of Mn and Cr in the surface layer are inhibited from dissolving.

FIGS. 7 and 8 are electron micrographs of a scale surface layer portion of Comparative Example 5 and Comparative Example 6 after application of 1.5 V to a gamma-ray electrode in a sulfuric acid solution of 80 g / L at 50 ° C for 120 seconds.

Referring to FIG. 7 showing the surface layer portion of Comparative Example 5, it was seen that the dissolution of the surface layer scale progressed considerably due to the high current density identified above. On the other hand, in FIG. 8, it was confirmed that dissolution of the surface layer scale of Comparative Example 6 having a high Mn content was inhibited.

When the formula (1) is satisfied within the range of the alloying element component range according to the present invention, the scale thickness is 0.115 to 0.130 占 퐉, and the high-Cr ferritic stainless steel pickle Showed good pickling ability under the condition.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited thereto. Those skilled in the art will recognize that other embodiments may occur to those skilled in the art without departing from the scope and spirit of the following claims. It will be understood that various changes and modifications may be made.

Claims (9)

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.02% or less of C, 0.3 to 0.6% of Si, 0.1 to 0.5% of Mn, 0.03% or less of P, 0.005% or less of S, 17.0 to 26.0% : 0.1 to 0.6%, Sn: not more than 0.1%, N: not more than 0.05%, the balance Fe and unavoidable impurities,
A high-Cr ferritic stainless steel satisfying the following formula (1) and excellent in pickling performance.
(1) 0.115? 0.123 - 0.0108 * Sn + 0.0151 * Si - 0.0147 * Mn + 0.0089 * Ni - 0.0105 * Sn * Si? 0.130
(Where Sn, Si, Mn, and Ni mean the content (weight%) of each element) The method according to claim 1,
In the stainless steel,
Cu: not more than 0.5%, and Al: not more than 0.01%. The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.02% or less of C, 0.3 to 0.6% of Si, 0.1 to 0.5% of Mn, 0.03% or less of P, 0.005% or less of S, 17.0 to 26.0% : 0.1 to 0.6%, Sn: not more than 0.1%, N: not more than 0.05%, the remaining Fe and unavoidable impurities;
Electrolytically pickling the cold-rolled annealed material; And
Sulfuric acid, and hydrofluoric acid,
The annealing heat treatment is performed at a temperature of 1,030 to 1,070 캜 within 3 minutes,
Wherein the scale thickness (占 퐉) of the cold-rolled annealed material satisfies the following formula (1).
(1) 0.115? 0.123 - 0.0108 * Sn + 0.0151 * Si - 0.0147 * Mn + 0.0089 * Ni - 0.0105 * Sn * Si? 0.130
(Where Sn, Si, Mn, and Ni mean the content (weight%) of each element) The method of claim 3,
Wherein the electrolytic pickling step comprises:
Neutral salt electrolytic acid pickling and sulfuric acid electrolytic pickling,
Wherein the neutral salt electrolytic bath and the sulfuric acid electrolytic bath have an applied current of 9 to 10 A / dm ² and a current application time of 90 seconds or less. 5. The method of claim 4,
Wherein the neutral salt electrolytic bath has a temperature of 70 to 80 캜 and the sulfuric acid electrolytic bath has a temperature of 40 to 50 캜. 5. The method of claim 4,
Wherein the neutral salt concentration of the neutral salt electrolytic acid is 180 to 220 g / L,
Wherein the sulfuric acid concentration of the sulfuric acid electrolytic pickling is 60 to 100 g / L. The method of claim 3,
And the redox potential (ORP) of the mixed acid solution is not less than 370 mV. The method of claim 3,
Wherein the mixed acid solution has a temperature of 45 to 55 占 폚. The method of claim 3,
The sulfuric acid concentration of the mixed acid solution is 80 to 150 g / L,
And the hydrofluoric acid concentration of the mixed acid solution is 20 to 30 g / L.

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