KR20190072279A - Ferritic stainless steel excellent in corrosion resistance and the manufacturing method for improving pickling property - Google Patents

Abstract

Disclosed are high Cr ferritic stainless steel with improved corrosion resistance and a manufacturing method for improving pickling. According to an embodiment of the present invention, the ferritic stainless steel with improved corrosion resistance comprises: 0.01-1.0 wt% of Si; 17-18.5 wt% of Cr; 0.01-0.6 wt% of Nb; 0.1-0.3 wt% of Cu; and 0.01-0.1 wt% of Sn. A ratio of Si to Sn is equal to or more than 3.0. Moreover, the ferritic stainless steel with improved corrosion resistance satisfies a formula (1) and a formula (2), wherein the formula (1) is 44.013 - 19.08*Si - 33.93*Cu - 40.616*Sn <= 30. Moreover, the formula (2) is represented by 0.09 + 0.458*Si + 0.145*Nb - 2.146*Sn <= 0.32.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a ferritic stainless steel having excellent corrosion resistance and a method for improving the pickling property of the ferritic stainless steel,

The present invention relates to a ferritic stainless steel excellent in corrosion resistance and a method for improving pickling resistance, and more particularly to a ferritic stainless steel which is capable of improving the pickling resistance of a scale caused by an increase in oxidation resistance of a high Cr ferritic stainless steel .

Automotive exhaust system SCR (SCR: Selective Catalytic Reduction) is a urea (aqueous urea) and ammonia (NH _3), NO _x gases to nitrogen (N ₂₎ and water (H ₂ O) through a catalyst by made by digesting It is used mainly for diesel heavy vehicles, but recently it is also used in general passenger diesel vehicles as environmental regulations are strengthened. In the process of decomposing the urea water at high temperature to produce NH ₃ , an ammonium carbamate (NH ₂ COONH ₄ ) having high corrosiveness is formed.

Conventionally, ceramics have been mainly used for the SCR catalyst carrier, and a ferritic stainless steel plate is used for the SCR catalyst carrier case made of the cylindrical ceramic. For this reason, the inside of the ferritic stainless steel sheet is required to have excellent corrosion resistance.

In particular, the operating environment of the SCR is periodically repeated in high temperature oxidizing environments and when the vehicle is in a running state, due to the deposition of condensed water in the stopped state. The hot working temperature is demanded a high-temperature oxidation properties of 600 ℃, the stationary included in the condensed water _{^{Cl -, NO 3 -, SO}} 4 2-, are both in the aqueous solution sex corrosion properties due to the NH ₄ ⁺ ions required . A high Cr ferritic stainless steel material of usually 17 wt% or more is used, and in order to improve the oxidation resistance at high temperature, the Si content may be increased. In this case, Si oxide is formed on the annealing scale and the base material interface during the annealing heat treatment, making it difficult to remove it in the neutral salt electrolytic pickling process.

Si oxide can be removed by immersion in a mixed acid solution containing nitric acid (HNO ₃ ) and hydrofluoric acid (HF) without being removed by a general electrolytic pickling process. Even if immersed in a mixed acid solution containing nitric acid and hydrofluoric acid, It is necessary to increase the concentration of hydrofluoric acid or increase the temperature to pick up the acid. However, when the concentration of hydrofluoric acid is increased, the cost of the acid increases, and when the temperature is increased, the amount of NO _x generated from the nitric acid increases, which is an environmental problem.

Therefore, there is a need for a ferritic stainless steel producing method which is easy to pick up in the neutral salt electrolytic pickling process while improving the corrosion resistance and oxidation resistance.

Embodiments of the present invention provide a ferritic stainless steel containing 17 to 18.5% by weight of Cr with excellent corrosion resistance, and also provide an acid pickling property of Si oxide present in the annealing scale through control of alloy components affecting corrosion resistance and acidity And to provide an improvement method.

A ferritic stainless steel excellent in corrosion resistance according to an embodiment of the present invention comprises 0.003 to 0.1% of C, 0.01 to 1.0% of Si, 0.01 to 1.0% of Mn, 0.05% or less of P, 0.05% or less of S, 0.005% or less of Cr, 17.0 to 18.5% of Cr, 0.01 to 0.03% of Ti, 0.01 to 0.6% of Nb, 0.1 to 0.3% of Cu, 0.01 to 0.1% of Sn, 0.003 to 0.03% of N, (Si / Sn) of 3.0 or more and satisfies the following formula (1).

(One) 44.013 - 19.08 * Si - 33.93 * Cu - 40.616 * Sn? 30

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

Further, according to an embodiment of the present invention, the stainless steel may satisfy the following formula (2).

(2) 0.09 + 0.458 * Si + 0.145 * Nb - 2.146 * Sn? 0.32

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

A method for improving pickling resistance of a ferritic stainless steel excellent in corrosion resistance according to an embodiment of the present invention is characterized by comprising 0.003 to 0.1% of C, 0.01 to 1.0% of Si, 0.01 to 1.0% of Mn, 0.05 to 1.0% of P, 0.003 to 0.03% of N, 0.01 to 0.1% of Sn, 0.01 to 0.1% of Sn, 0.01 to 0.03% of Nb, 0.01 to 0.6% of Nb, Neutralizing the cold-rolled annealed material containing the remaining Fe and unavoidable impurities and having a ratio of Si to Sn (Si / Sn) of 3.0 or more; And a mixed acid comprising nitric acid and hydrofluoric acid, wherein the cold-rolled annealed material satisfies the following formula (2).

(2) 0.09 + 0.458 * Si + 0.145 * Nb - 2.146 * Sn? 0.32

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

Further, according to an embodiment of the present invention, the cold-rolled annealed material can satisfy the following formula (1).

(One) 44.013 - 19.08 * Si - 33.93 * Cu - 40.616 * Sn? 30

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

According to an embodiment of the present invention, in the electrolytic pickling step, the applied current of the neutral salt electrolytic bath is 8 to 12 A / dm ² Lt; / RTI &gt;

According to an embodiment of the present invention, in the step of immersing in the mixed acid, the concentration of nitric acid in the mixing tank may be 80 to 100 g / L and the concentration of hydrofluoric acid may be 10 to 15 g / L.

According to an embodiment of the present invention, in the step of immersing in the mixed acid, the temperature of the mixing tank may be 40 to 45 ° C, and the immersion time may be 40 to 50 seconds.

The ferritic stainless steel according to the embodiment of the present invention is excellent in corrosion resistance and can improve the durability in the SCR operating environment and improve the pickling performance in the cold rolling process and improve the productivity.

1 is a graph showing the results of Si analysis of GDS for pickling property evaluation of the present invention.
2 is a graph showing the correlation between the equation (1) and the equation (2) of the present invention.
3 is a TEM photograph showing the annealing scale of the inventive example and comparative example according to the embodiment of the present invention.

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.

The present invention proposes an alloy composition and parameters that facilitate the electrolytic pickling of Si oxide in the annealing scale in order to secure the corrosion resistance in the SCR of an automobile exhaust system and hence the pickling problem. The optimum conditions for electrolytic pickling and mixed acid immersion for productivity improvement are also presented.

As described above, since the operating environment of the SCR is repeatedly shown by the high-temperature oxidizing environment and the corrosive environment caused by the condensed water, Si is added to the high Cr ferritic stainless steel in order to improve the oxidation resistance, .

In order to solve the above problems, in the present invention, various alloying elements of ferritic stainless steels containing 17 to 18.5% by weight of Cr were evaluated for their influence on corrosion resistance in a SCR simulation environment, and for evaluating pickling performance, The presence of Si oxide was analyzed and the influence of the component system on the neutral salt electrolytic pickling resistance was evaluated. As a result, the alloy composition for improving the corrosion resistance and acidity in the SCR simulation environment could be derived as follows.

A ferritic stainless steel excellent in corrosion resistance according to an embodiment of the present invention comprises 0.003 to 0.1% of C, 0.01 to 1.0% of Si, 0.01 to 1.0% of Mn, 0.05% or less of P, 0.05% or less of S, 0.005% or less of Cr, 17.0 to 18.5% of Cr, 0.01 to 0.03% of Ti, 0.01 to 0.6% of Nb, 0.1 to 0.3% of Cu, 0.01 to 0.1% of Sn, 0.003 to 0.03% of N, (Si / Sn) of 3.0 or more and satisfies the following formula (1).

(One) 44.013 - 19.08 * Si - 33.93 * Cu - 40.616 * Sn? 30

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 0.003 to 0.1%.

C is an element which 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 0.1% or less. However, if the content is too low, the strength is excessively lowered, and the lower limit may be limited to 0.003%.

The content of Si is 0.01 to 1.0%.

Si is an element added for deoxidation of molten steel during steelmaking and stabilization of ferrite. In the present invention, 0.01% or more Si is added. It is also an element that helps improve oxidation resistance and corrosion resistance at high temperatures. However, when the content is excessive, the acidity is deteriorated and is limited to 1.0% or less.

The content of Mn is 0.01 to 1.0%.

Mn is an element effective for improving oxidation resistance. In the present invention, 0.01% or more is added, and more preferably, 0.2% or more is added. However, if the content is excessive, the generation of Mn-based fumes is rapidly increased at the time of welding, and the weldability is deteriorated and the ductility of the steel is deteriorated due to the formation of excessive MnS precipitates.

The content of P is 0.05% 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 0.05% 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 18.5%.

Cr is an element effective for improving the corrosion resistance of steel and is limited to 17.0 to 18.5% Cr-containing ferritic stainless steel in the present invention.

The content of Ti is 0.01 to 0.3%.

Ti is an element that fixes C and N to reduce the amount of solid solution C and solid solution N in the steel and is effective in improving the corrosion resistance of steel. In the present invention, 0.01% or more is added, and more preferably 0.1% or more is added. However, if the content is excessive, not only the production cost increases but also surface defects are caused by the formation of Ti inclusions. The content is limited to 0.3% or less, more preferably 0.25% or less.

The content of Nb is 0.01 to 0.6%.

When the amount of Nb is less than 0.01%, there is a problem that the high temperature strength of the material is lowered because Nb is small in the material, and when the amount of Nb is less than 0.6% The oxide layer becomes thick at the interface when annealed, and the acidity is deteriorated.

The content of Cu is 0.1 to 0.3%.

Cu improves the corrosion resistance in an acidic atmosphere by improving the corrosion resistance. However, if Cu is added excessively, there is a risk of lowering the formal potential in the chloride atmosphere, which is limited to 0.3% or less.

The content of Sn is 0.01 to 0.1%.

Sn is an element which suppresses Si oxide growth and improves corrosion resistance in an acidic atmosphere. In the present invention, 0.01% or more Sn is added. 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 0.003 to 0.03%.

N is an element which plays a role of accelerating recrystallization by precipitation of austenite during hot rolling. In the present invention, 0.003% or more is added. However, if the content is excessive, the ductility of the steel is deteriorated, and it is limited to 0.03% or less.

When Si, Cu, and Sn are added so as to satisfy the above formula (1), excellent corrosion resistance can be exhibited in the SCR simulation environment where urea water exposure at 600 캜 or higher and condensed water deposition at 80 캜 are repeated.

However, when the content of Cu or Si among Si, Cu, and Sn, which are elements for improving corrosion resistance, is low, the corrosion resistance standard required in the SCR operating environment may not be satisfied. Therefore, the Si / Sn ratio (Si / Sn) of 3.0 or more can be satisfied in order to secure the corrosion resistance in the SCR operating environment.

Further, according to an embodiment of the present invention, a ferritic stainless steel excellent in corrosion resistance can satisfy the following formula (2).

(2) 0.09 + 0.458 * Si + 0.145 * Nb - 2.146 * Sn? 0.32

The above formula (2) is a component parameter for improving the pickling property in the cold rolling pickling process during the production process, and is a parameter that suppresses Si oxide which has the greatest influence on pickling performance, Nb which relates to oxide thickness during cold rolling annealing, Of Sn. When Si, Nb and Sn are added so as to satisfy the formula (2), the acid pickling property can be improved in the cold-rolling pickling step to be described later.

Next, a method for improving pickling performance of a ferritic stainless steel excellent in corrosion resistance according to an embodiment of the present invention will be described.

A method for improving pickling resistance of a ferritic stainless steel excellent in corrosion resistance according to an embodiment of the present invention is characterized by comprising 0.003 to 0.1% of C, 0.01 to 1.0% of Si, 0.01 to 1.0% of Mn, 0.05 to 1.0% of P, 0.003 to 0.03% of N, 0.01 to 0.1% of Sn, 0.01 to 0.1% of Sn, 0.01 to 0.03% of Nb, 0.01 to 0.6% of Nb, Neutralizing the cold-rolled annealed material containing the remaining Fe and unavoidable impurities and having a ratio of Si to Sn (Si / Sn) of 3.0 or more; And a mixed acid comprising nitric acid and hydrofluoric acid, wherein the cold-rolled annealed material satisfies the following formula (2).

(2) 0.09 + 0.458 * Si + 0.145 * Nb - 2.146 * Sn? 0.32

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

As described above, the formula (2) is a component parameter for improving the pickling property in the cold rolling pickling step during the production process, and includes Si which has the greatest influence on pickling performance, Nb relating to oxide thickness during cold rolling annealing, Si And Sn which inhibits oxide growth. When Si, Nb and Sn are added so as to satisfy the expression (2), the thickness of Si oxide in the annealing scale can be reduced and the pickling property can be improved.

However, when the content of Cu or Si, which is an element improving the corrosion resistance, is low, the pickling property may be improved but the corrosion resistance standard required in the SCR operating environment may not be satisfied. Therefore, the formula (1) and the Si / Sn ratio (Si / Sn) of 3.0 or more can be satisfied in order to secure the corrosion resistance in the SCR operating environment.

The method for improving the pickling property of a ferritic stainless steel excellent in corrosion resistance according to the present invention comprises the steps of: neutralizing a cold-rolled annealed material; And a mixed acid comprising nitric acid and hydrofluoric acid.

The cold-rolled annealed material may be, for example, a cold-rolled steel sheet annealed at 1,030 캜 or higher and 1,050 캜 or lower.

The cold-rolled annealed material is subjected to a neutral salt electrolytic pickling step to dissolve the scale, and in the electrolytic pickling step, the applied current of the neutral salt electrolytic bath is 8 to 12 A / dm ² Lt; / RTI &gt; When the applied electric current of the neutral salt electrolytic cell is less than 8 A / dm ^2, surface potential which can dissolve the annealing scale is not formed, and there is a risk of misplaced, and when the current is more than 12 A / dm ² , The applied current is preferably adjusted to be 8 to 12 A / dm ² .

Since the Cr and Fe oxide layers are removed on the surface of the 17 to 18.5% Cr-containing ferritic stainless steel cold-rolled steel sheet subjected to the neutral salt electrolytic pickling, only the Si oxide layer is left, and after the neutral salt electrolytic pickling, .

In the step of immersing in the mixed acid, the hydrofluoric acid concentration in the mixing tank may be 10 to 15 g / L. The hydrofluoric acid dissolves the Si oxide and binds it in the form of H ₂ SiF ₆ or the like, thereby removing the Si oxide from the surface of the steel sheet. If the concentration of hydrofluoric acid is less than 10 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 15 g / L, It can be rough.

On the other hand, in order to maintain the acidic force of hydrofluoric acid in the mixed acid solution for removing the Si oxide layer, it is preferable to adjust the nitric acid concentration in the mixing bath to a range of 80 to 100 g / L.

According to an embodiment of the present invention, in the step of immersing in the mixed acid, the temperature of the mixing tank may be 40 to 45 ° C, and the immersion time may be 40 to 50 seconds.

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

Example

The slabs having the compositions shown in Table 1 below were prepared, hot rolled and hot-rolled and annealed, and cold-rolled and cold-annealed to obtain 2.0 mm cold rolled steel sheets.

division Composition (% by weight) C Si Mn Cr Ni Ti Nb Cu Sn N Comparative Example 1 0.01 0.39 0.25 18.0 0.1 0.15 0.52 0 0 0.0077 Comparative Example 2 0.011 0.231 0.22 17.5 0.1 0.222 0.35 0 0 0.0069 Comparative Example 3 0.01 0.206 0.25 18.1 0.1 0.157 0.37 0.15 0 0.0074 Comparative Example 4 0.01 0.5 0.25 18.1 0.1 0.123 0.2 0.15 0 0.0087 Comparative Example 5 0.011 0.403 0.25 18.1 0.1 0.172 0.34 0.2 0 0.009 Comparative Example 6 0.01 0.39 0.24 18.3 0.1 0.124 0.37 0.3 0 0.0079 Comparative Example 7 0.01 0.21 0.25 18.1 0.1 0.15 0.37 0 0.09 0.0073 Comparative Example 8 0.01 0.2 0.25 18.0 0.1 0.15 0.37 0 0.072 0.0073 Comparative Example 9 0.01 0.55 0.25 18.0 0.1 0.123 0.45 0.17 0.11 0.0079 Inventory 1 0.012 0.43 0.25 18.0 0.1 0.146 0.32 0.146 0.03 0.0073 Inventory 2 0.01 0.45 0.26 18.0 0.1 0.152 0.35 0.156 0.052 0.0073 Inventory 3 0.01 0.51 0.26 18.0 0.1 0.152 0.4 0.153 0.077 0.0073

1. Evaluation of corrosion resistance and acidity

Table 2 shows the corrosion resistance evaluation results and the pickling resistance evaluation results according to the elements which affect the corrosion resistance and pickling performance of the inventive and comparative steels shown in Table 1 above.

The corrosion resistance evaluation was performed by repeating 20 times of exposure to urea water for 2 hours at 600 ° C and for 0.5 hour at 80 ° C condensate to simulate the SCR environment. At high temperature, the atmospheric gas was composed of O ₂ , NO _x gas, H ₂ O, SO ₂ , CO and N ₂ components and the condensed water environment was obtained by adding Cl ^- , NO ₃ ^- , SO ₄ ^2- and NH ₄ ⁺ and the pH was adjusted to 3. When the weight loss was less than 30 mg / cm ² , the test was judged to be acceptable. The acceptance was denoted by ○, and the rejection was denoted by ×.

The pickling resistance of the cold rolled annealed steel sheet was evaluated by GDS and TEM. The cold rolling annealed steel sheet was cold rolled at a temperature of 1,040 캜 for about 157 seconds after cold rolling. The highest acidity was observed in the annealing scale. Was combined with neutral salt electrolytic pickling with mixed acid deposition, electrolytic neutral salt pickling and mixed acid deposition, respectively was carried out for 40 ~ 60 seconds, electrolytic neutral salt conditions were _{80 ℃, Na 2 SO 4 200g} / L, the applied current is 10A / dm ² , mixed acid deposition conditions were 45 ° C, HNO ₃ 100 g / L and HF 12 g / L. The acidity evaluation was made by passing through the optical microscope after pickling, and when no surface residual scale was present, it was judged as passing. The acceptance was marked with ○, and the rejection was marked with ×.

1 is a graph showing the results of GDS Si analysis for pickling property evaluation of the present invention. As shown in FIG. 1, the acidity was evaluated by multiplying the peak value by the Half Maximum Full Width (HMFW) in the analyzed Si profile.

division Si Nb Cu Sn Corrosion resistance evaluation Assessment of pickling Si / Sn Equation (1):
Weight loss
(mg / cm ²⁾ Judgment Equation (2):
Si peak
Area Judgment Comparative Example 1 0.39 0.52 0 0 37.3 × 0.352 × - Comparative Example 2 0.231 0.35 0 0 39.5 × 0.254 ○ - Comparative Example 3 0.206 0.37 0.15 0 35 × 0.246 ○ - Comparative Example 4 0.5 0.2 0.15 0 29 ○ 0.360 × - Comparative Example 5 0.403 0.34 0.2 0 29.5 ○ 0.321 × - Comparative Example 6 0.39 0.37 0.3 0 27 ○ 0.322 × - Comparative Example 7 0.21 0.37 0 0.09 35.0 × 0.100 ○ 2.33 Comparative Example 8 0.2 0.37 0 0.072 36.0 × 0.150 ○ 2.92 Comparative Example 9 0.55 0.45 0.17 0.11 24 ○ 0.200 ○ 5.00 Inventory 1 0.43 0.32 0.146 0.03 29 ○ 0.264 ○ 14.33 Inventory 2 0.45 0.35 0.156 0.052 27 ○ 0.225 ○ 8.65 Inventory 3 0.51 0.4 0.153 0.077 26.5 ○ 0.230 ○ 6.62

As shown in Table 2, it can be seen that when Si, Cu, and Sn are added, the corrosion resistance is improved.

In Comparative Example 3, Cu was added, but Sn was not added to satisfy the formula (1), so that the corrosion resistance was poor. In Comparative Examples 4 to 6, corrosion resistance was improved by the addition of Si and Cu, but it was found that the pickling property evaluation was unsatisfactory in order to heat pickling. On the other hand, in the case of Comparative Examples 2 and 3, it was confirmed that the acid pickling property was excellent but the corrosion resistance was improved.

In Comparative Examples 7 and 8, it was confirmed that the acidity is improved but the corrosion resistance is relatively improved, as an example in which Cu is not added and only Sn is added. This indicates that the Si content is excellent due to the decrease of the Si content but the corrosion resistance is insufficient. In particular, the Si / Sn value is not more than 3.0.

In the case of Comparative Example 9, both Cu and Sn were added to provide excellent corrosion resistance and acidity, but edge cracking occurred due to deterioration of hot workability during hot rolling in the manufacturing process. It was confirmed that the content of Sn was more than 0.1% and the hot workability was lowered, and the upper limit of Sn was controlled to be 0.1% or less.

2 is a graph showing the correlation between the equation (1) and the equation (2) of the present invention. Fig. 2 shows the values of the formulas (1) and (2) shown in Table 2 and shows the inventive area satisfying the required corrosion resistance in SCR. The inventive area has corrosion resistance, .

3 is a TEM photograph showing the annealing scale of the inventive example and comparative example according to the embodiment of the present invention. The thickness of the Si oxide layer in the annealing scale (b) of Inventive Example 2 was smaller than that of the annealing scale (a) of Comparative Example 6, Was found to be thin.

2. Pickling conditions

Table 3 below shows the degree of improvement in pickling performance as the actual alloy component is changed by changing the pickling conditions with respect to the steel grades listed in Table 1 above.

division Si Nb Cu Sn Neutral salt
Applied current
(A / dm ² ) Concentration Concentration (g / L) Temperature
(° C) deposition
time
(sec) nitric acid Foshan Comparative Example 1 0.39 0.52 0 0 15 100 20 45 60 Comparative Example 5 0.403 0.34 0.2 0 15 120 15 50 60 Inventory 1 0.43 0.32 0.146 0.03 12 80 15 45 45 Inventory 2 0.45 0.35 0.156 0.052 8 90 10 45 40 Inventory 3 0.51 0.4 0.153 0.077 8 100 10 40 40

In the case of Comparative Examples 1 and 5, pickling was possible at a neutral salt applied current of 15 A / dm ² , a hydrofluoric acid concentration of 15 g / L or more, a temperature of 45 ° C or higher and a deposition time of 60 seconds. / dm ² , and it was found that acid pickling was possible under the conditions of mixed acid deposition which was lower than that of the comparative example, with a fluoric acid concentration of 10 to 15 g / L, a temperature of 40 to 45 ° C, and a deposition time of 40 to 45 seconds.

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 (7)

0.003 to 0.1% of Si, 0.01 to 1.0% of Mn, 0.01 to 1.0% of Mn, 0.05% or less of P, 0.005% or less of S, 17.0 to 18.5% of Cr, 0.01 to 0.03% 0.01 to 0.6% of Nb, 0.1 to 0.3% of Cu, 0.01 to 0.1% of Sn, 0.003 to 0.03% of N, Fe and unavoidable impurities,
The ratio of Si to Sn (Si / Sn) is 3.0 or more,
A ferritic stainless steel excellent in corrosion resistance satisfying the following formula (1).
(1) 44.013 - 19.08 * Si - 33.93 * Cu - 40.616 * Sn? 30
(Here, Si, Cu and Sn mean the content (% by weight) of each element) The method according to claim 1,
In the stainless steel,
A ferritic stainless steel excellent in corrosion resistance satisfying the following formula (2).
(2) 0.09 + 0.458 * Si + 0.145 * Nb - 2.146 * Sn? 0.32
(Where Si, Nb, and Sn mean the content (weight%) of each element) 0.003 to 0.1% of Si, 0.01 to 1.0% of Mn, 0.01 to 1.0% of Mn, 0.05% or less of P, 0.005% or less of S, 17.0 to 18.5% of Cr, 0.01 to 0.03% (Si / Sn) of from 3.0 to 3.0%, Nb: 0.01 to 0.6%, Cu: 0.1 to 0.3%, Sn: 0.01 to 0.1%, N: 0.003 to 0.03%, and balance Fe and unavoidable impurities. Or more of the cold rolled annealed sheet; And
Nitric acid, and hydrofluoric acid,
Wherein the cold-rolled annealed material satisfies the following formula (2): &quot; (1) &quot;
(2) 0.09 + 0.458 * Si + 0.145 * Nb - 2.146 * Sn? 0.32
(Where Si, Nb, and Sn mean the content (weight%) of each element) The method of claim 3,
The cold-
A method for improving pickling performance of a ferritic stainless steel excellent in corrosion resistance satisfying the following formula (1).
(1) 44.013 - 19.08 * Si - 33.93 * Cu - 40.616 * Sn? 30
(Here, Si, Cu and Sn mean the content (% by weight) of each element) The method of claim 3,
In the electrolytic pickling step,
The applied current of the neutral salt electrolytic cell is 8 to 12 A / dm ² A method for improving the pickling property of a ferritic stainless steel excellent in corrosion resistance. The method of claim 3,
In the step of immersing in the mixed acid,
Wherein the concentration of nitric acid in the mixing tank is 80 to 100 g / L, and the concentration of hydrofluoric acid is 10 to 15 g / L. The method of claim 3,
In the step of immersing in the mixed acid,
Wherein the temperature of the mixing tank is 40 to 45 占 폚 and the immersion time is 40 to 50 seconds.

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