KR102030153B1 - Ferritic stainless steel excellent in corrosion resistance and the manufacturing method for improving pickling property - Google Patents

Abstract

Disclosed are a high Cr ferritic stainless steel excellent in corrosion resistance and a manufacturing method which can improve pickling problems.
Ferritic stainless steel excellent in corrosion resistance according to an embodiment of the present invention and a method for improving pickling thereof are Si: 0.01 to 1.0%, Cr: 17 to 18.5%, Nb: 0.01 to 0.6%, Cu: 0.1 to 0.3% , Sn: 0.01-0.1%, Si / Sn is 3.0 or more, and satisfy | fills Formula (1) and (2).
(1) 44.013-19.08 * Si-33.93 * Cu-40.616 * Sn ≤ 30
(2) 0.09 + 0.458 * Si + 0.145 * Nb-2.146 * Sn ≤ 0.32

Description

Ferritic stainless steel with excellent corrosion resistance and its pickling resistance improvement method {FERRITIC STAINLESS STEEL EXCELLENT IN CORROSION RESISTANCE AND THE MANUFACTURING METHOD FOR IMPROVING PICKLING PROPERTY}

The present invention relates to a ferritic stainless steel having excellent corrosion resistance and a method for improving pickling thereof, and more particularly, to a manufacturing method capable of improving the pickling resistance problem of scale caused by the improved oxidation resistance of high Cr ferritic stainless steel. It is about.

Selective Catalytic Reduction (SCR) for automobiles is made by ammonia (NH ₃ ), which is produced by decomposing aqueous urea, and converts NO _x gas into nitrogen (N ₂ ) and water (H ₂ O) through a catalyst. As an environmental technology that reduces and harms, it is mainly used for diesel large vehicles, but is also used for general passenger diesel vehicles due to the recent tightening of environmental regulations. In the process of decomposing the urea water under high temperature to form NH ₃ , a highly corrosive ammonium carbamate (NH ₂ COONH ₄ ) is formed.

Conventionally, ceramics have been mainly used for the SCR catalyst carrier, and ferritic stainless steel sheets are used for the SCR catalyst carrier case made of the cylindrical ceramic. For this reason, the inside of a ferritic stainless steel plate is calculated | required by the outstanding corrosion resistance.

In particular, the operating environment of the SCR is periodically repeated a high temperature oxidation environment and the corrosion environment due to the deposition of the stationary condensate while the vehicle is running. 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 . Typically, 17 wt% or more high Cr ferritic stainless steels are used, and in order to improve high temperature oxidation resistance, the Si content may be increased. In this case, during the annealing heat treatment, Si oxide is formed at the interface between the annealing scale and the base material, which makes it difficult to remove it in the neutral salt electrolytic pickling process.

Si oxide can be removed by deposition in a mixed acid solution containing nitric acid (HNO ₃ ) and hydrofluoric acid (HF) without being removed by a general electrolytic pickling process, and takes a long time even if it is deposited in a mixed acid solution containing nitric acid and hydrofluoric acid. In addition, it is necessary to increase the concentration of hydrofluoric acid or to raise the temperature before pickling. However, increasing the hydrofluoric acid concentration increases the acid cost, and increasing the temperature increases the amount of NO _x generated from nitric acid, which is an environmental problem.

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

Embodiments of the present invention provide a ferritic stainless steel having excellent corrosion resistance containing 17 to 18.5% by weight of Cr, and pickling resistance of Si oxide present in the annealing scale through control of alloy components affecting corrosion resistance and pickling resistance. To provide a way to improve.

Ferritic stainless steel excellent in corrosion resistance according to an embodiment of the present invention, in weight%, C: 0.003-0.1%, Si: 0.01-1.0%, Mn: 0.01-1.0%, P: 0.05% or less, S: 0.005% or less, Cr: 17.0-18.5%, Ti: 0.01-0.03%, Nb: 0.01-0.6%, Cu: 0.1-0.3%, Sn: 0.01-0.1%, N: 0.003-0.03%, remaining Fe and inevitable It contains impurities and the ratio of Si and Sn (Si / Sn) is 3.0 or more, and satisfies the following formula (1).

(1) 44.013-19.08 * Si-33.93 * Cu-40.616 * Sn ≤ 30

Here, Si, Cu, Sn means content (weight%) of each element.

In addition, 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, Sn means content (weight%) of each element.

The method for improving pickling of ferritic stainless steel having excellent corrosion resistance according to an embodiment of the present invention is, by weight, C: 0.003-0.1%, Si: 0.01-1.0%, Mn: 0.01-1.0%, P: 0.05% S: 0.005% or less, Cr: 17.0-18.5%, Ti: 0.01-0.03%, Nb: 0.01-0.6%, Cu: 0.1-0.3%, Sn: 0.01-0.1%, N: 0.003-0.03%, Neutral salt electrolytic pickling of the cold rolled annealing material containing the remaining Fe and unavoidable impurities and having a ratio of Si and Sn (Si / Sn) of 3.0 or more; And immersing in a mixed acid including nitric acid and hydrofluoric acid, wherein the cold rolled annealing material satisfies Equation 2 below.

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

Here, Si, Nb, Sn means content (weight%) of each element.

In addition, according to one embodiment of the present invention, the cold rolled annealing material may satisfy the following formula (1).

(1) 44.013-19.08 * Si-33.93 * Cu-40.616 * Sn ≤ 30

Here, Si, Cu, Sn means content (weight%) of each element.

In addition, according to an embodiment of the present invention, the applied current of the neutral salt electrolytic cell in the electrolytic pickling step is 8 to 12A / dm ² Can be.

Further, according to one embodiment of the present invention, the nitric acid concentration of the mixed acid bath in the step of immersing in the mixed acid may be 80 to 100g / L, the hydrofluoric acid concentration may be 10 to 15g / L.

Further, according to one embodiment of the present invention, the temperature of the mixed acid bath in the step of immersing in the mixed acid may be 40 to 45 ℃, immersion time may be 40 to 50 seconds.

Ferritic stainless steel according to an embodiment of the present invention is excellent in corrosion resistance to improve the durability in the SCR operating environment, it is possible to improve the pickling properties in the cold rolling process to improve productivity.

1 is a graph showing the results of Si analysis of GDS for pickling evaluation of the present invention.
2 is a graph showing the correlation between equation (1) and equation (2) of the present invention.
3 is a TEM photograph showing an annealing scale of the invention 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 examples are presented to fully convey the spirit of the present invention to those skilled in the art. The invention is not limited to the examples presented herein but may be embodied in other forms. The drawings may omit illustrations of parts not related to the description in order to clarify the present invention, and may be exaggerated to some extent in order to facilitate understanding.

In addition, when a part is said to "include" a certain component, which means that it may further include other components, except to exclude other components unless otherwise stated.

Singular expressions include plural expressions unless the context clearly indicates an exception.

The present invention proposes an alloy component system and parameters that facilitate electrolytic pickling of Si oxides in annealing scales in order to secure corrosion resistance and thus pickling properties in automobile exhaust system SCRs. In addition, the optimum conditions of electrolytic pickling and mixed acid immersion for productivity improvement are suggested.

As described above, the operating environment of the SCR is a high temperature oxidizing environment and a corrosion environment caused by condensate water repeatedly appear, so that Si and the like are added to the high Cr ferritic stainless steel to improve oxidation resistance. It is happening.

In order to solve the above problems, in order to solve the above problems, the effect of the alloying properties of the ferritic stainless steel containing 17 to 18.5% by weight of Cr on the corrosion resistance in the SCR simulation environment was evaluated, and also annealing scale to evaluate the pickling resistance The effect of the component system on the neutral salt electrolytic pickling was analyzed by analyzing the Si oxide present. As a result, the alloy component system for improving the corrosion resistance and pickling resistance in the SCR simulation environment can be derived as follows.

Ferritic stainless steel excellent in corrosion resistance according to an embodiment of the present invention, in weight%, C: 0.003-0.1%, Si: 0.01-1.0%, Mn: 0.01-1.0%, P: 0.05% or less, S: 0.005% or less, Cr: 17.0-18.5%, Ti: 0.01-0.03%, Nb: 0.01-0.6%, Cu: 0.1-0.3%, Sn: 0.01-0.1%, N: 0.003-0.03%, remaining Fe and inevitable It contains impurities and the ratio of Si and Sn (Si / Sn) is 3.0 or more, and satisfies the following formula (1).

(1) 44.013-19.08 * Si-33.93 * Cu-40.616 * Sn ≤ 30

Hereinafter, the reason for numerical limitation of the alloying element content in the embodiment of the present invention will be described. In the following, the unit is% by weight unless otherwise specified.

The content of C is 0.003 to 0.1%.

C is an element that greatly affects the strength of the steel, and when the content is excessive, the strength of the steel is excessively increased and the ductility is reduced, so it is limited to 0.1% or less. However, if the content is too low, the strength is excessively reduced, the lower limit can be limited to 0.003%.

The content of Si is 0.01 to 1.0%.

Si is an element added for deoxidation and ferrite stabilization of molten steel during steelmaking. In the present invention, Si is added at least 0.01%. In addition, it is an element that helps to improve high temperature oxidation resistance and corrosion resistance, but when the content is excessive, pickling resistance is lowered and limited to 1.0% or less.

The content of Mn is 0.01 to 1.0%.

Mn is an element effective for improving the oxidation resistance, and 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 weldability decreases due to the rapid increase of Mn-based fume during welding, and the ductility of the steel decreases due to excessive MnS precipitate formation.

The content of P is 0.05% or less.

P is an inevitable impurity contained in steel, and is an element that is a major cause of grain boundary corrosion or hot workability during pickling. 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 inevitable impurity contained in steel, and is an element that is the main cause of segregation at grain boundaries and impairs hot workability. Therefore, it is preferable to control the content as low as possible. In the present invention, the upper limit of the S content is managed 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 effective to reduce the amount of solid solution C and solid solution N in steel by fixing C and N and to improve the corrosion resistance of the steel. In the present invention, Ti is added at least 0.01%, more preferably at least 0.1%. However, if the content is excessive, not only the manufacturing cost increases rapidly, but also causes surface defects due to the formation of Ti-based inclusions, which is limited to 0.3% or less, and more preferably 0.25% or less.

The content of Nb is 0.01 to 0.6%.

Nb preferentially combines with C and N to form a precipitate that suppresses the deterioration of corrosion resistance.If the amount of Nb is less than 0.01%, there is a problem that the high temperature strength of the material decreases due to less Nb dissolved in the material, and exceeds 0.6%. When annealed, the oxide layer becomes thick at the interface, resulting in poor pickling.

The content of Cu is 0.1 to 0.3%.

Cu is a corrosion resistance improving element and improves corrosion resistance in an acidic atmosphere. However, when excessively added Cu, there is a risk of lowering the official potential in the chloride atmosphere is limited to 0.3% or less.

The content of Sn is 0.01 to 0.1%.

Sn is an element that suppresses the growth of Si oxide and improves the corrosion resistance in an acidic atmosphere. In the present invention, Sn is added at least 0.01%. However, if the content is excessive, it is limited to 0.1% or less as it inhibits hot workability.

The content of N is 0.003 to 0.03%.

N is an element that precipitates austenite during hot rolling and promotes recrystallization. In the present invention, N is added at least 0.003%. However, if the content is excessive, the ductility of the steel is reduced, so it is limited to 0.03% or less.

When Si, Cu, and Sn are added to satisfy Equation (1), excellent corrosion resistance may be exhibited in an SCR simulation environment in which urea water exposure at 600 ° C. or higher and condensate deposition at 80 ° C. are repeated.

However, when the content of Cu or Si among the corrosion resistance improving elements Si, Cu, and Sn is low, it may occur that the corrosion resistance requirements required in the SCR operating environment are not met. Therefore, in order to secure corrosion resistance in the SCR operating environment, the ratio of Si and Sn (Si / Sn) may satisfy 3.0 or more.

In addition, according to an embodiment of the present invention, the ferritic stainless steel excellent in corrosion resistance may satisfy the following formula (2).

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

Equation (2) is a component parameter for improving pickling properties in the cold rolling pickling process in the manufacturing process, and Si having the greatest influence on pickling properties, Nb related to oxide thickness during cold rolling annealing, and Si oxide growth are suppressed. The relationship of Sn is shown. When Si, Nb, and Sn are added so as to satisfy the above formula (2), the pickling improvement effect may be exhibited in the cold rolling pickling process described later.

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

The method for improving pickling of ferritic stainless steel having excellent corrosion resistance according to an embodiment of the present invention is, by weight, C: 0.003-0.1%, Si: 0.01-1.0%, Mn: 0.01-1.0%, P: 0.05% S: 0.005% or less, Cr: 17.0-18.5%, Ti: 0.01-0.03%, Nb: 0.01-0.6%, Cu: 0.1-0.3%, Sn: 0.01-0.1%, N: 0.003-0.03%, Neutral salt electrolytic pickling of the cold rolled annealing material containing the remaining Fe and unavoidable impurities and having a ratio of Si and Sn (Si / Sn) of 3.0 or more; And immersing in a mixed acid including nitric acid and hydrofluoric acid, wherein the cold rolled annealing material satisfies Equation 2 below.

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

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

As described above, Equation (2) is a component parameter for improving pickling properties in the cold rolling pickling process in the manufacturing process, Si having the greatest influence on pickling properties, Nb related to the oxide thickness during cold rolling annealing, and Si The relationship of Sn which suppresses oxide growth is shown. When Si, Nb, and Sn are added so that the cold rolled annealing material satisfies Equation (2), it is possible to reduce the thickness of the Si oxide in the annealing scale, thereby improving the pickling property.

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

The method for improving pickling of ferritic stainless steel having excellent corrosion resistance according to the present invention includes: neutral salt electrolytic pickling of a cold rolled annealing material; And immersing in a mixed acid including nitric acid and hydrofluoric acid.

The cold rolled annealing material may be, for example, a cold rolled steel sheet annealed at a temperature of 1,030 ° C or more and 1,050 ° C or less.

The cold rolled annealing material undergoes a neutral salt electrolytic pickling step to dissolve the scale. In the electrolytic pickling step, an applied current of the neutral salt electrolyzer is 8 to 12 A / dm ^2. Can be. If the applied current of the neutral salt electrolyzer is less than 8A / dm ^2, the surface potential that can dissolve the annealing scale is not formed, so that the pickling may occur, and if it is more than 12A / dm ² , the surface erosion may occur due to the superacid. The applied current is preferably adjusted to be 8 to 12 A / dm ² .

Since the Cr and Fe oxide layers are removed and only the Si oxide layer remains on the surface of the 17 to 18.5% Cr-containing ferritic stainless steel cold rolled steel subjected to the neutral salt electrolytic pickling, a mixed acid solution containing nitric acid and hydrofluoric acid after the neutral salt electrolytic pickling Perform the step of dipping in.

In the step of immersion in the mixed acid, the hydrofluoric acid concentration of the mixed acid tank may be 10 to 15g / L. The hydrofluoric acid dissolves the Si oxide and bonds it in the form of H ₂ SiF ₆ to remove the Si oxide from the steel plate surface. At this time, when the hydrofluoric acid concentration is less than 10g / L, there is a lack of dissolving power to the Si oxide layer may cause the problem of the acid pickling on the surface of the steel sheet. Can be rough.

On the other hand, in order to maintain the pickling force of hydrofluoric acid in the mixed acid solution for removing the Si oxide layer, the nitric acid concentration of the mixed acid bath is preferably adjusted in the range of 80 to 100 g / L.

Further, according to one embodiment of the present invention, the temperature of the mixed acid bath in the step of immersing in the mixed acid may be 40 to 45 ℃, immersion time may be 40 to 50 seconds.

Hereinafter will be described in more detail through a preferred embodiment of the present invention.

Example

The slabs having the composition shown in Table 1 below were prepared, and the produced slabs were hot rolled and hot rolled, followed by cold rolling and cold rolled annealing 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 Inventive Example 1 0.012 0.43 0.25 18.0 0.1 0.146 0.32 0.146 0.03 0.0073 Inventive Example 2 0.01 0.45 0.26 18.0 0.1 0.152 0.35 0.156 0.052 0.0073 Inventive Example 3 0.01 0.51 0.26 18.0 0.1 0.152 0.4 0.153 0.077 0.0073

1. Corrosion resistance and pickling evaluation

Table 2 below shows the corrosion resistance evaluation results and pickling evaluation results according to the elements affecting the corrosion resistance and pickling properties for the steels of the invention examples and comparative examples described in Table 1 above.

Corrosion resistance was measured by weighting 20 hours of 2 hours of urea water exposure at 600 ° C. and 0.5 hours of condensate at 80 ° C. to simulate the SCR environment. In the high temperature gas are O _2, NO _x gas, H ₂ O, SO _2, was made up of CO, N ₂ component, condensed water environment is ^{_{Cl -, NO 3 -, SO}} 4 2-, by adding a solution of NH ₄ ⁺ The pH was evaluated to be 3. As a result of corrosion resistance evaluation, when the weight loss was less than 30 mg / cm ² , it was judged as a pass.

In the evaluation of pickling property, the annealing scale of the cold rolled annealing steel sheet which was performed for about 157 seconds at the cold rolling annealing temperature of 1,040 ° C after cold rolling to 2.0 mm was analyzed by GDS and TEM. The pickling factor was shown to be the biggest factor affecting pickling in the annealing scale through Si component analysis. Neutral salt electrolytic pickling and mixed acid deposition were performed in parallel. Neutral salt electrolytic pickling and mixed acid deposition were performed for 40 to 60 seconds, and neutral salt electrolysis conditions were 80 ° C, Na ₂ SO ₄ 200 g / L, and applied current was 10 A / dm. ² , mixed acid deposition conditions are 45 ℃, HNO ₃ 100 g / L and HF 12 g / L. The pickling evaluation was judged as pass when there was no surface residual scale through optical microscopy after pickling, and the pass was marked as ○ and the fail was denoted as ×.

1 is a graph showing the results of GDS Si analysis for pickling evaluation of the present invention. The pickling property was determined by multiplying the peak value and the HMFW (Half Maximum Full Width) in the Si profile analyzed as shown in FIG. 1 to show pickling properties.

division Si Nb Cu Sn Corrosion Resistance Evaluation Pickling evaluation 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 Inventive Example 1 0.43 0.32 0.146 0.03 29 ○ 0.264 ○ 14.33 Inventive Example 2 0.45 0.35 0.156 0.052 27 ○ 0.225 ○ 8.65 Inventive Example 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 the corrosion resistance is improved when Si, Cu, Sn is added.

In Comparative Example 3, Cu was added but Sn was not added, which did not satisfy Equation (1), resulting in inferior corrosion resistance. In Comparative Examples 4 to 6, the corrosion resistance was improved by addition of Si and Cu, but it was found that pickling evaluation was failed because the pickling property was inferior. On the other hand, although the pickling property was excellent in Comparative Examples 2 and 3, it was confirmed that corrosion resistance was inferior.

Comparative Examples 7 and 8 are examples of the case where Cu is not added and only Sn is added, and pickling is improved, but the corrosion resistance is relatively inferior. This indicates that the pickling property is excellent due to the decrease of the Si content but the corrosion resistance is insufficient. In particular, the Si / Sn value did not satisfy 3.0 or more.

In Comparative Example 9, both Cu and Sn were added to provide excellent corrosion resistance and pickling resistance, but edge cracks occurred due to a decrease in hot workability during hot rolling during the manufacturing process. This indicates that the Sn content exceeds 0.1% and the hot workability is lowered, and the upper limit of Sn should be controlled to 0.1% or less.

2 is a graph showing the correlation between equation (1) and equation (2) of the present invention. Fig. 2 shows the invention examples region which satisfies the corrosion resistance required for SCR by displaying the values of the formulas (1) and (2) described in Table 2 above. Excellent.

3 is a TEM photograph showing an annealing scale of the invention example and comparative example according to the embodiment of the present invention. As a result of analyzing the thickness of the Si oxide layer in the annealing scale according to the actual addition of Sn by TEM photograph, the thickness of the Si oxide layer in the annealing scale (b) of Inventive Example 2 was compared with that of the annealing scale (a) of Comparative Example 6. Was confirmed to be thin.

2. Pickling condition

For the steel grades listed in Table 1 above, the pickling conditions were changed and the degree of pickling performance was improved as the actual alloy components were changed.

division Si Nb Cu Sn Neutral salt
Current applied
(A / dm ² ) Mixed acid concentration (g / L) Temperature
(℃) 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 Inventive Example 1 0.43 0.32 0.146 0.03 12 80 15 45 45 Inventive Example 2 0.45 0.35 0.156 0.052 8 90 10 45 40 Inventive Example 3 0.51 0.4 0.153 0.077 8 100 10 40 40

In 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 can be lowered, the concentration of hydrofluoric acid 10 ~ 15g / L, temperature 40 ~ 45 ℃, deposition time 40 ~ 45 seconds, it was found that the pickling is possible in the mixed acid deposition conditions relaxed than the comparative example.

As described above, the exemplary embodiments of the present invention have been described, but the present invention is not limited thereto, and a person of ordinary skill in the art may be within the scope and spirit of the following claims. It will be understood that various changes and modifications are possible.

Claims (7)

By weight, C: 0.003-0.1%, Si: 0.01-1.0%, Mn: 0.01-1.0%, P: 0.05% or less, S: 0.005% or less, Cr: 17.0-18.5%, Ti: 0.01-0.03% , Nb: 0.01-0.6%, Cu: 0.1-0.3%, Sn: 0.01-0.1%, N: 0.003-0.03%, remaining Fe and inevitable impurities,
The ratio of Si and Sn (Si / Sn) is 3.0 or more,
Ferritic stainless steel excellent in corrosion resistance satisfying the following formulas (1) and (2).
(1) 44.013-19.08 * Si-33.93 * Cu-40.616 * Sn ≤ 30
(2) 0.09 + 0.458 * Si + 0.145 * Nb-2.146 * Sn ≤ 0.32
(Si, Cu, Nb, Sn means the content (wt%) of each element) delete By weight, C: 0.003-0.1%, Si: 0.01-1.0%, Mn: 0.01-1.0%, P: 0.05% or less, S: 0.005% or less, Cr: 17.0-18.5%, Ti: 0.01-0.03% , Nb: 0.01 to 0.6%, Cu: 0.1 to 0.3%, Sn: 0.01 to 0.1%, N: 0.003 to 0.03%, remaining Fe and unavoidable impurities, and the ratio of Si and Sn (Si / Sn) is 3.0 Neutral salt electrolytic pickling of the above cold rolled annealing material; And
It comprises; immersing in a mixed acid containing nitric acid and hydrofluoric acid;
The cold-rolled annealing material is a method of improving pickling properties of ferritic stainless steel excellent in corrosion resistance satisfying the following formula (1) and formula (2).
(1) 44.013-19.08 * Si-33.93 * Cu-40.616 * Sn ≤ 30
(2) 0.09 + 0.458 * Si + 0.145 * Nb-2.146 * Sn ≤ 0.32
(Si, Cu, Nb, Sn means the content (wt%) of each element) delete The method of claim 3, wherein
In the electrolytic pickling step,
The applied current of the neutral salt electrolyzer is 8 to 12 A / dm ² A method for improving pickling of ferritic stainless steel with excellent phosphorus corrosion resistance. The method of claim 3, wherein
In the step of immersing in the mixed acid,
Nitric acid concentration of the mixed acid tank is 80 to 100g / L, the hydrofluoric acid concentration is 10 to 15g / L pickling improvement method of ferritic stainless steel excellent in corrosion resistance. The method of claim 3, wherein
In the step of immersing in the mixed acid,
A method for improving pickling of ferritic stainless steel having excellent corrosion resistance, wherein the temperature of the mixed acid bath is 40 to 45 ° C. and the immersion time is 40 to 50 seconds.

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