KR102020512B1 - High chromium ferritic stainless steel excellent in pickling property and its pickling method - Google Patents

Abstract

Disclosed is a ferritic stainless steel and a pickling method thereof, by which the Mn oxide thickness and the internal Si oxide thickness of the surface layer scale of Si and Nb-added high Cr ferritic stainless steel can be adjusted to ensure easy pickling.
High Cr ferritic stainless steel having excellent pickling properties according to an embodiment of the present invention, in weight%, C: 0.02% or less, Si: 0.3 to 0.6%, Mn: 0.1 to 0.5%, P: 0.03% or less, S: 0.005% or less, Cr: 17.0-26.0%, Ni: 0.6% or less, Nb: 0.1-0.6%, Sn: 0.1% or less, N: 0.05% or less, remaining Fe and unavoidable impurities, and the following formula ( 1) is satisfied.
(1) 0.115 ≤ 0.123-0.0108 * Sn + 0.0151 * Si-0.0147 * Mn + 0.0089 * Ni-0.0105 * Sn * Si ≤ 0.130

Description

High Cr ferritic stainless steel with excellent pickling properties and pickling method {HIGH CHROMIUM FERRITIC STAINLESS STEEL EXCELLENT IN PICKLING PROPERTY AND ITS PICKLING METHOD}

The present invention relates to a ferritic stainless steel having excellent pickling properties and a method for pickling the same, and more particularly, to improve the electrolytic pickling and mixed acid immersion pickling of Si and Nb-added high Cr ferritic stainless steels. The present invention relates to a ferritic stainless steel and a pickling method thereof, by adjusting the thickness of an internal Si oxide to ensure scale thickness that is easy to pickle.

In general, ferritic stainless steel is classified into low Cr ferritic stainless steel and high Cr ferritic stainless steel according to Cr content. In general, the case of Cr content of 11 to 14% by weight is called low Cr ferritic stainless steel, and the case of Cr content of 17 to 26% by weight is called high Cr ferritic stainless steel.

Since the characteristics of the scale formed during the annealing heat treatment vary depending on the Cr content, the pickling method according to the Cr content should be performed differently. In general, in the case of low Cr ferritic stainless steel, the scale is thickly formed during annealing heat treatment, and in the case of high Cr ferritic stainless steel, the scale is thinner than the low Cr ferritic stainless steel.

In addition, there is a difference in the heat treatment temperature during annealing according to the characteristics of the steel type, the higher the annealing temperature, the thicker the scale is formed, the higher the content of Cr in the scale. This scale not only degrades the appearance quality of the product, but may also act as a factor of deteriorating corrosion resistance by starting corrosion from the oxidizing scale, and thus, it is necessary to remove the scale formed on the surface through the pickling process.

Si and Nb are elements that enhance high temperature oxidation resistance and high temperature strength, respectively, and are often added to ferritic stainless steels used in high temperature applications. However, when such an element is added, there is a problem that the pickling property is significantly lowered.

In order to improve the electrolytic pickling and mixed acid immersion pickling of Si and Nb-added high Cr ferritic stainless steels, the present invention can adjust the thickness of the Mn oxide and the internal Si oxide of the surface layer scale to secure a scale thickness that is easy to pickle. It is to provide a ferritic stainless steel and its pickling method.

High Cr ferritic stainless steel having excellent pickling properties according to an embodiment of the present invention, in weight%, C: 0.02% or less, Si: 0.3 to 0.6%, Mn: 0.1 to 0.5%, P: 0.03% or less, S: 0.005% or less, Cr: 17.0-26.0%, Ni: 0.6% or less, Nb: 0.1-0.6%, Sn: 0.1% or less, N: 0.05% or less, remaining Fe and unavoidable impurities, and the following formula ( 1) is satisfied.

(1) 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, Ni means the content (wt%) of each element.

In addition, according to an embodiment of the present invention, the stainless steel may further include Cu: 0.5% or less, Al: 0.01% or less.

Pickling method of high Cr ferritic stainless steel according to an embodiment of the present invention, in weight%, C: 0.02% or less, Si: 0.3 to 0.6%, Mn: 0.1 to 0.5%, P: 0.03% or less, S: Annealing heat treatment of the cold rolled steel sheet containing 0.005% or less, Cr: 17.0 to 26.0%, Ni: 0.6% or less, Nb: 0.1 to 0.6%, Sn: 0.1% or less, N: 0.05% or less, remaining Fe and unavoidable impurities step; Electrolytic pickling the cold rolled annealing material; And immersing in a mixed acid solution containing sulfuric acid and hydrofluoric acid, wherein the annealing heat treatment is performed at 1,030 to 1,070 ° C. within 3 minutes, and the scale thickness (μm) of the cold rolled annealing material is expressed by Equation 1 below. Satisfies.

(1) 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, Ni means the content (wt%) of each element.

In addition, according to one embodiment of the present invention, the electrolytic pickling includes neutral salt electrolytic pickling and sulfuric acid electrolytic pickling, and the applied current of the neutral salt electrolytic bath and the sulfuric acid electrolytic bath is 9 to 10 A / dm ² , and the current is applied. The time may be within 90 seconds.

Further, according to an embodiment of the present invention, the neutral salt electrolyzer may have a temperature of 70 to 80 ° C., and the sulfuric acid electrolyzer may have a temperature of 40 to 50 ° C.

Further, according to an embodiment of the present invention, 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.

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

In addition, according to an embodiment of the present invention, the temperature of the mixed acid solution may be 45 to 55 ℃.

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

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

In addition, it is possible to secure excellent surface quality after pickling by optimizing the electrolytic pickling and mixed pickling conditions.

1 is a graph showing the optimum scale thickness range according to the change of Mn content and Si content.
2 is a photograph showing a scale cross-sectional shape of Comparative Example 5.
3 is a graph illustrating an analysis of alloying components according to the scale depth d of FIG. 2.
4 is a photograph showing a scale cross-sectional shape of Comparative Example 6.
5 is a graph illustrating an analysis of alloying components according to the scale depth d of FIG. 4.
Figure 6 is a graph showing the current change with time after applying the cold rolled annealing steel sheet of Comparative Example 5 and Comparative Example 6 in comparison with the red electrode in 80g / L sulfuric acid solution.
7 and 8 are electron micrographs taken of the scale surface layer part after applying 1.5 V relative to the magenta electrode in a sulfuric acid solution of 50 ° C. and 80 g / L for 120 seconds for Comparative Examples 5 and 6. FIG.

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.

Typically, in manufacturing stainless steel cold rolled steel sheets, physical descaling, such as brush treatment or shotball blasting, sodium sulfate, sulfuric acid or the like, in order to obtain an excellent surface quality by removing the oxidized scale formed on the steel sheet and to improve the corrosion resistance of the steel sheet Various methods, such as electrolytic descaling using a nitric acid electrolyte and the like, chemical descaling by a salt bath or mixed acid, etc., have been performed. This process is referred to as a 'pickling process'.

In this pickling process, one-step electrolytic pickling such as electrolytic descaling and two-step mixed acid immersion processes such as chemical descaling are distinguished.

In the first stage electrolytic pickling process, when the Mn and Cr composite oxides in the scale surface layer are thick, the dissolution reaction is delayed in the electrolytic pickling process. On the contrary, when the Si oxide is thickly formed therein, the dissolution reaction is delayed in the two stage mixed acid immersion process. Therefore, the thickness of the surface layer Mn oxide and the thickness of the Si oxide should be adjusted to facilitate pickling.

As described above, the ferritic stainless steel requires high temperature oxidation resistance or high temperature strength depending on the intended use, and Si and Nb are added to improve the ferrite stainless steel. Occurs.

In the present invention, in order to improve the pickling properties of high Cr ferritic stainless steel containing 17 wt% or more of Cr, it was intended to optimize the scale thickness by controlling the content of Si, Mn, Ni, Sn.

As a result of analyzing the scale of cold rolled steel sheet subjected to cold rolling annealing using GDS (Glow Discharge Spectroscope), the effect of alloying elements on the scale thickness could be analyzed. Among the alloying elements, Si, Mn, Ni, and Sn influence the scale thickness, and Si and Sn interact with each other. Si and Ni increase the scale thickness and Mn and Sn reduce the scale thickness. In addition, Si and Sn interact with each other to reduce scale thickness.

By quantifying the alloying element influence on the scale thickness of the high Cr ferritic stainless steel through this, the scale thickness (μm) range can be expressed as in the following equation (1).

(1) 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 added with Si and Nb is present in the range of 0.115 to 0.130 μm, pickling properties may be improved.

High Cr ferritic stainless steel having excellent pickling properties according to an embodiment of the present invention, in weight%, C: 0.02% or less, Si: 0.3 to 0.6%, Mn: 0.1 to 0.5%, P: 0.03% or less, S: 0.005% or less, Cr: 17.0-26.0%, Ni: 0.6% or less, Nb: 0.1-0.6%, Sn: 0.1% or less, N: 0.05% or less, remaining Fe and inevitable impurities.

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 0.02% or less.

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 lowered, so it is limited to 0.02% or less.

The content of Si is 0.3 to 0.6%.

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

The content of Mn is 0.1 to 0.5%.

Mn is an element effective for improving the oxidation resistance, and 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, the pickling property is significantly lowered, so the upper limit thereof is limited to 0.5%.

The content of P is 0.03% 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 0.03% 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 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 present invention in the range of 17.0 to 26.0%.

The content of Ni is 0.6% or less.

Ni in ferritic stainless steel can be treated as an impurity, but is incorporated in part during scrap melting. The upper limit of Ni is limited to 0.6%, but the Ni content included in part controls the scale thickness by the above formula (1).

The content of Nb is 0.1 to 0.6%.

Nb preferentially combines with C and N to form precipitates that suppress the deterioration of corrosion resistance.If the amount of Nb is less than 0.1%, there is a problem that the high temperature strength of the material falls 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 Sn is 0.1% or less.

Sn inhibits the growth of Si oxide upon addition and improves the corrosion resistance in acidic atmosphere. However, if the content is excessive, it is limited to 0.1% or less as it inhibits hot workability.

The content of N is 0.05% or less.

N is an element that precipitates austenite during hot rolling and promotes recrystallization, but when the content is excessive, N decreases the ductility of the steel and is limited to 0.05% or less.

In addition, according to an embodiment of the present invention, Cu: 0.5% or less, Al: 0.01% or less may be further included.

The content of Cu is 0.5% or less.

Cu is a corrosion resistance improvement element, and can be added in order to improve corrosion resistance in an acidic atmosphere. However, when excessively added Cu, there is a risk of lowering the official potential in the chloride atmosphere, it is limited to 0.5% or less.

The content of Al is 0.01% or less.

Al is a strong deoxidizer and serves to lower the oxygen content in molten steel, but excessive addition causes lower ductility at room temperature, so the upper limit thereof is 0.01% and does not need to be contained.

1 is a graph showing the optimum scale thickness range according to the change of Mn content and Si content.

1 shows the optimum scale thickness range (white region) in which pickling property is improved according to Mn and Si contents after fixing Sn content to 0.06% and Ni content to 0.5%. In order to ensure excellent pickling properties in high Cr ferritic stainless steels containing Si and Nb, 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. A significant drop in pickling can be expected if the Mn content exceeds 0.5% in a Si content below 0.6%. This is related to the range limitation of Si and Mn in the alloying elements of the present invention.

When the optimum scale thickness range within the above-described alloy element component range satisfies Equation (1), it may exhibit excellent pickling properties in a pickling process of a cold rolled annealing steel sheet to be described later.

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

Pickling method of high Cr ferritic stainless steel according to an embodiment of the present invention, in weight%, C: 0.02% or less, Si: 0.3 to 0.6%, Mn: 0.1 to 0.5%, P: 0.03% or less, S: Annealing heat treatment cold rolled steel sheet containing 0.005% or less, Cr: 17.0-26.0%, Ni: 0.6% or less, Nb: 0.1-0.6%, Sn: 0.01-0.1%, N: 0.05% or less, remaining Fe and unavoidable impurities Doing; Electrolytic pickling the cold rolled annealing material; And immersing in a mixed acid solution containing sulfuric acid and hydrofluoric acid, wherein the annealing heat treatment is performed at 1,030 to 1,070 ° C. within 3 minutes, and the scale thickness (μm) of the cold rolled annealing material is expressed by Equation 1 below. Satisfies.

(1) 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 the numerical limitation of the alloy element content is as described above.

The cold rolled steel sheet satisfying the alloying element component system and formula (1) according to the present invention may be annealed for 3 minutes at 1,030 to 1,070 ° C. to form a scale having a thickness of 0.115 to 0.130 μm on the surface of the steel sheet to improve pickling.

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

The applied current of the neutral salt electrolyzer and sulfuric acid electrolyzer in the electrolytic pickling step is 9 to 10 A / dm ² , and the current application time may be within 90 seconds. If the applied current is less than 9A / dm ^2, the surface potential that can dissolve the annealing scale is not formed, so the pickling may occur. If the applied current is more than 10A / dm ² , the surface erosion may occur due to the over-pickling. It is preferable to adjust the ratio to 10 A / dm ² .

Further, the neutral salt concentration of 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. And it is preferable that neutral salt electrolytic cell temperature is 70-80 degreeC, and the temperature of a sulfuric acid electrolytic cell is 40-50 degreeC.

Since the Mn, Cr and Fe oxide layers are removed and only the Si oxide layer remains on the surface of the high-Cr ferrite cold rolled annealing material subjected to neutral salt electrolytic pickling and sulfuric acid electrolytic pickling, after electrolytic pickling, it is immersed in a mixed acid solution containing sulfuric acid and hydrofluoric acid. Follow the steps.

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 combines it in the form of H ₂ SiF ₆ to remove the Si oxide from the surface of the steel sheet. At this time, when the hydrofluoric acid concentration is less than 20g / 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. The sulfuric acid concentration is preferably adjusted in the range of 80 to 150 g / L in order to maintain the pickling force 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 temperature of the mixed acid solution is preferably maintained in the range of 45 to 55 ° C.

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, the manufactured slabs were hot rolled and hot rolled and then cold rolled and cold rolled at 1,050 ° C. for 2 minutes and 30 seconds to obtain 2.0 mm cold rolled annealing steel sheets. The scale thickness of the cold rolled annealing steel sheet was measured using a GDS (Glow Discharge Spectroscope), and evaluated as the depth up to the maximum concentration of Si oxide present inside. Thus, the actual scale thickness may be thicker than the thicknesses listed in Table 1.

division Composition (% by weight) scale
thickness
(Μm) 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 Inventive Example 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 Inventive Example 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 Inventive Example 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 Inventive Example 4 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 Inventive Example 5 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 steel grades outside the scale thickness range according to Formula (1) of the present invention, and Inventive Examples 1 to 5 are steel grades whose scale thickness corresponds to the range of the present invention.

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

3 is a graph illustrating an analysis of alloying components according to the scale depth d of FIG. 2. Referring to FIG. 3, it can be seen that the main component of the outer layer scale is Cr oxide, and Mn and Fe oxides are partially dissolved. Moreover, it turns out that Si oxide which is an inner layer scale developed more than an outer layer scale. In Table 1, it can be seen that Comparative Example 5 has a low Mn content of 0.18%. When the Mn content is low, the development of the composite oxide of Mn and Cr is delayed, but it can be seen that it promotes the development of internal Si oxide. As a result, the scale thickness was measured to be 0.1897 μm, and since the Si oxide thickness was thick, pickling was difficult in the mixed acid immersion step.

4 is a photograph showing a scale cross-sectional shape of Comparative Example 6. Referring to FIG. 4, Comparative Example 6 also includes an outer layer scale and an inner layer scale. Unlike Comparative Example 5, the thickness of the outer layer scale is thinner and the development of the inner layer scale is suppressed. It was also found that the scale thickness was reduced as a whole.

5 is a graph illustrating an analysis of alloying components according to the scale depth d of FIG. 4. Referring to FIG. 5, it can be seen that the main components of the outer layer skew are Cr and Mn oxides, and Fe oxides are also dissolved in considerable amounts. In addition, the inner layer scale was Si oxide. It was found that Mn oxide was developed at the surface layer, and growth of internal Si oxide was suppressed. In Table 1, Comparative Example 6 confirms that the Mn content is as high as 0.50%, and it can be seen that the overall scale thickness shows a tendency to decrease when the Mn content is high. As a result, the scale thickness was measured to be 0.1003 μm, and the development of Mn oxide was expected to cause difficulties in the electrolytic pickling step.

Subsequently, the cold rolled annealing specimens of Table 1 were subjected to one-step neutral salt electrolytic pickling, sulfuric acid electrolytic pickling, and two-step mixed acid immersion pickling. Neutral salt electrolytic pickling was applied at 0.1 A / cm 2 in a solution of Na ₂ SO ₄ at 75 ° C. and 200 g / L. Sulfuric acid electrolytic pickling was applied at 0.1 A / cm 2 in a solution of H ₂ SO ₄ at 50 ° C. and 100 g / L. Mixed acid immersion was immersed for 180 seconds in the solution which mixed 55 degreeC, sulfuric acid 100g / L, and hydrofluoric acid 28g / L.

FIG. 6 is a graph showing a change in current with time after cold rolled annealing steel sheets of Comparative Example 5 and Comparative Example 6 were applied with 1.5 V in 80 g / L sulfuric acid solution.

Referring to FIG. 6, the comparative example 5 having a low Mn content shows a high current density of 10,000 mA / cm 2. On the other hand, Comparative Example 6 having a high Mn content shows a very low current density. That is, when the Mn content is high, it can be seen that the oxides of the surface layer portions Mn and Cr are inhibited from dissolution.

7 and 8 are electron micrographs taken of the scale surface layer part after applying 1.5 V relative to the magenta electrode in a sulfuric acid solution of 50 ° C. and 80 g / L for 120 seconds for Comparative Examples 5 and 6. FIG.

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

As such, it was possible to confirm the change in the scale configuration according to the Mn content, and when the formula (1) was satisfied within the alloy element component range according to the present invention, the scale thickness was 0.115 to 0.130 μm, indicating that pickling of high Cr ferritic stainless steel It showed excellent pickling under the conditions.

As described above, 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 (9)

By weight%, C: 0.02% or less, Si: 0.3-0.6%, Mn: 0.1-0.5%, P: 0.03% or less, S: 0.005% or less, Cr: 17.0-26.0%, Ni: 0.6% or less, Nb : 0.1 to 0.6%, Sn: 0.1% or less, N: 0.05% or less, remaining Fe and inevitable impurities,
Cu: 0.5% or less, Al: 0.01% or less further,
High Cr ferritic stainless steel excellent in pickling properties satisfying 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
(Sn, Si, Mn, Ni refer to the content (wt%) of each element) delete By weight%, C: 0.02% or less, Si: 0.3-0.6%, Mn: 0.1-0.5%, P: 0.03% or less, S: 0.005% or less, Cr: 17.0-26.0%, Ni: 0.6% or less, Nb : Annealing heat treatment of the cold rolled steel sheet containing 0.1 to 0.6%, Sn: 0.1% or less, N: 0.05% or less, remaining Fe and unavoidable impurities;
Electrolytic pickling the cold rolled annealing material; And
It includes; immersing in a mixed acid solution containing sulfuric acid and hydrofluoric acid,
The annealing heat treatment is carried out within 3 minutes at 1,030 to 1,070 ℃,
The electrolytic pickling step,
It includes neutral salt electrolytic pickling and sulfuric acid electrolytic pickling, the applied current of the neutral salt electrolytic bath and sulfuric acid electrolytic bath is 9 to 10A / dm2, the current application time is within 90 seconds,
The temperature of the neutral salt electrolytic cell is 70 to 80 ° C, the temperature of the sulfuric acid electrolytic cell is 40 to 50 ° C, the neutral salt concentration of the neutral salt electrolytic pickling is 180 to 220 g / L, and the sulfuric acid of the sulfuric acid electrolytic pickling Concentration is 60-100 g / L,
The redox potential (ORP) of the mixed acid solution is 370 mV or more, the temperature of the mixed acid solution is 45 to 55 ° C, 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,
Scale thickness (μm) of the cold rolled annealing material is a high Cr ferritic stainless steel pickling method that 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
(Sn, Si, Mn, Ni refer to the content (wt%) of each element)


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