KR20180107422A - Stainless steel with excellent surface gloss and corrosion resistance, method of method for treating surface the same - Google Patents

Abstract

The present invention relates to stainless steel with excellent surface gloss and corrosion resistance and a method for treating surface thereof that are capable of removing metals causing corrosion through simple processes to thus improve an amount of chrome among the metals exposed to the surface thereof, so that chromium oxide can be thicker and tighter in a passivation process, thereby having excellent surface gloss and corrosion resistance and being utilized in more various industrial fields. According to the present invention, the method for treating a surface of stainless steel with excellent surface gloss and corrosion resistance includes the steps of: (1) selectively etching a second component among a first component and the second component contained on the surface of a stainless base metal; (2) applying electro polishing liquid to the selectively etched stainless base metal to perform electro polishing; and (3) applying a passivation liquid to the electro polished stainless base metal to form an oxidation film.

Description

TECHNICAL FIELD The present invention relates to a stainless steel having excellent surface gloss and corrosion resistance and a surface treatment method of the stainless steel,

More particularly, the present invention relates to a stainless steel which is improved in corrosion resistance, discoloration resistance and luster through selective etching of stainless steel base material, electrolytic polishing and passivation treatment, And a surface treatment method.

Stainless steel is used as a component in various industries requiring corrosion resistance such as automobile members, construction members, high-temperature piping, and kitchen appliances. Stainless steels generally can be classified as austenitic stainless steels, ferritic stainless steels, austenite-ferritic stainless steels and martensitic stainless steels, and in particular, austenitic steels such as SUS304 and SUS301 Stainless steel is widely used in various industries because of its excellent processability.

Stainless steel uses various alloying elements such as copper (Cu) and manganese (Mn) for the main materials such as iron (Fe), chrome (Cr) and nickel However, corrosion and discoloration may occur over time in a high temperature and acidic hybrid environment. In particular, in a high-temperature oxidative atmosphere such as a muffler for an automobile, red rust corrosion or yellow feel may occur, which may result in deterioration of the mechanical properties of the material and further deterioration of functional or appearance sensibility.

In order to improve this, a method of applying austenitic stainless steel to a steel sheet by brilliant annealing and temper rolling has been introduced. However, such a brass annealing and temper rolling is not limited to a steel sheet which can be used only for gloss- .

In addition, techniques for improving corrosion resistance and surface luster by using a stainless alloy material, modifying the surface of a stainless steel, and changing the structure at an atomic unit have been introduced, It is difficult to realize a stainless steel having improved corrosion resistance and surface gloss, and there is no report on a technique that is chemically stable and does not deteriorate inherent glossiness in a high temperature and oxidizing atmosphere such as automobile muffler.

Accordingly, corrosion of stainless steel does not occur even in a high-temperature and oxidizing atmosphere, and inherent glossiness is prevented from deteriorating, and further processing and additives are not required, which contributes to economical efficiency and process simplification, It is urgent to develop a technique for stainless steel having excellent luster.

Japanese Patent Application Laid-Open No. 10-2011-0104631

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a method of selectively etching a material causing corrosive corrosion on a stainless steel surface to form more chromium oxide on the surface of stainless steel, And stainless steel showing high discoloration resistance at high temperatures.

The present invention also provides a method of selectively removing a corrosion-inducing substance such as iron, chromium, nickel, copper, and manganese present in an alloy component of stainless steel to expose a chromium component having excellent corrosion resistance to the surface, It is another object of the present invention to provide a manufacturing method for stainless steel which is capable of reducing the unevenness and densely forming the chromium oxide layer to further strengthen the corrosion resistance.

In order to solve the above-described problems, the present invention provides a method of manufacturing a stainless steel substrate, comprising the steps of: (1) selectively etching a first component and a second component contained in a surface portion of a stainless steel base material; (2) (3) treating the electrolytically polished stainless base material with a passive processing solution to form an oxide film; The present invention also provides a surface treatment method of stainless steel excellent in corrosion resistance and gloss.

According to an embodiment of the present invention, the step (1) may be a step of treating the stainless steel base material with a selective etching solution to remove the second component.

In addition, the second component may be more susceptible to oxidation than the first component.

In addition, the first component may include chromium, and the second component may include at least one of iron, nickel, and copper.

The selective etchant may further contain 25 to 200 parts by weight of a perchloric acid, 50 to 200 parts by weight of hydrogen peroxide, 25 to 200 parts by weight of gluconic acid, 15 to 100 parts by weight of oxalic acid, and 5 to 50 parts by weight of a surfactant based on 100 parts by weight of nitric acid. .

Also, the stainless base material may be treated with the selective etching solution at a temperature of 30 ° C to 100 ° C for 2 to 60 minutes.

The weight percentage of the first component included in the surface of the stainless steel base material subjected to the step (1) may be greater than the weight percentage of the first component contained in the stainless base metal.

The electrolytic polishing solution may contain 200 to 350 parts by weight of phosphoric acid and 0.5 to 25 parts by weight of a surfactant based on 100 parts by weight of sulfuric acid.

Further, the stainless base material can be treated in the electrolytic polishing solution at a temperature of 30 ° C to 120 ° C and a current density of 30 to 90 A / dm ² for 10 to 500 seconds.

The passive solution may contain 30 to 200 parts by weight of hydrogen peroxide, 15 to 100 parts by weight of citric acid, 100 to 250 parts by weight of water, and 0.3 to 25 surfactants per 100 parts by weight of nitric acid.

The present invention also provides a stainless steel including an oxide film for the first component formed on the surface of the stainless steel base material and having a surface roughness (Ra) of 0.07 탆 or less.

According to an embodiment of the present invention, the stainless steel may have a corrosion potential (Ecorr) of 360 mV or more.

In addition, the stainless steel has a gloss of more than 1000 GU at 20 DEG, more than 600 GU at 60 DEG, and a gloss of more than 100 GU at 85 DEG.

According to the present invention, by removing the metals causing corrosion of the stainless steel through a simple process, the content of chrome in the metal exposed to the stainless steel surface is increased, so that the chromium oxide is formed thicker and denser in the passivation process, It is possible to realize a stainless steel having excellent gloss and it can be utilized for various industries.

1 is a flowchart showing a method of manufacturing stainless steel according to the present invention,
FIGS. 2A and 2B are schematic views showing a state where a second component is removed from stainless steel through selective etching;
FIG. 3 is a schematic view showing a state in which surface irregularities of stainless steel are removed through an electrolytic polishing step,
4 is a schematic view showing a passivation step of forming an oxide film on the surface of electrolytically polished stainless steel,
5 is a graph showing a polarization curve according to each step of a stainless steel, and
6A is a view showing the surface gloss of stainless steel, FIG. 6B is a view showing the surface gloss of stainless steel after the selective etching and electrolytic polishing step, and FIG. 6C is a view showing surface gloss after passivation.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same reference numerals are assigned to the same or similar components throughout the specification.

Generally, stainless steel is used as a material for various industries ranging from aerospace industry to electronic components and building materials because of its excellent corrosion resistance and gloss. Such stainless steel contains a main material such as iron (Fe), chromium (Cr), and nickel (Ni) as a base metal and various metals such as copper (Cu) and manganese With the development of the industry, it has been modified and manufactured for various purposes.

On the other hand, the stainless steel described above exhibits high corrosion resistance in a normal atmosphere, but corrosion and discoloration specific to the metal under high temperature or acidic conditions may occur, which may cause mechanical property deterioration of the stainless steel itself, There is a fear that the quality of sensibility due to appearance discoloration is lowered. Particularly, when the stainless steel is used as a vehicle material such as a muffler or a tail trim, the muffler or the tail trim is corroded by the oxidizing gas such as NOx, SOx or the like, which is generated in the vehicle, and the target mechanical and / Problems may arise, and further, as the appearance is discolored, the gloss is degraded, which limits the use as a vehicle material.

Recently, as a solution to this problem, research is being conducted on a technique for protecting the outer surface of a stainless steel with an oxide film by passivating the stainless steel. That is, a method of protecting an outer surface of a stainless steel by oxidizing chromium (Cr) having relatively high corrosion resistance existing in stainless steel to form an oxide film, thereby improving the luster of stainless steel and preventing discoloration have.

However, the amount of chromium existing in general stainless steel is not sufficient to form an oxide film through the above-described method, and even if the oxidation film of chromium is formed so as to cover the entire outer surface, the content of chromium is insufficient, The uniformity may be lowered. As a result, the muffler or tail trim using stainless steel as a material may cause partial discoloration and corrosion, so that it is difficult to achieve the intended mechanical and / or functional performance and improve the sensibility.

In addition, when the content of chromium in the stainless steel itself is increased so that the oxide film can be formed uniformly, there arises a problem depending on the brittleness and the workability can be significantly lowered. Therefore, only the passivation treatment for forming the oxide film has a limitation in solving the above- have.

Accordingly, the present invention provides a method for surface treatment of stainless steel, wherein the chromium oxide film is uniformly formed on the surface without increasing the content of chromium by further adding to the stainless steel itself, thereby simultaneously exhibiting excellent corrosion resistance and gloss.

For this, a surface treatment method of stainless steel according to the present invention (1) a step of selectively etching a first component and a second component contained in a surface portion of a stainless steel base material, (2) a step of selectively etching the selectively etched stainless- And (3) treating the electrolytically polished stainless base material with a passivation solution to form an oxide film.

In step (1), the step of selectively etching the first and second components included in the surface portion of the stainless steel base material is performed.

The first component and the second component are both metal components included in stainless steel, and in particular, the first component includes a metal component that is more difficult to oxidize than the second component. According to one example, when the stainless steel according to the present invention comprises iron (Fe), chromium (Cr), nickel (Ni), copper (Cu), the first component may include chromium, The component may comprise at least one or more of iron, nickel or copper.

On the other hand, selective etching means that a stainless steel base material is oxidized by oxidizing metal which is easily oxidized among metal components. According to one example, when the first component contains chromium and the second component comprises at least one of iron, nickel, and copper, iron, nickel, and copper are metals that are more likely to be oxidized than chromium. Selective etching can remove iron and nickel or copper that can cause corrosion by pitting at the surface of the base material, and can lead to exposure of unremoved chrome. That is, as shown in FIGS. 2A and 2B, the surface portion A of the stainless steel can be etched through selective etching to form irregularities (A '). At this time, the valleys between the concavities and convexities may be formed by removing the second component, and the first component may be exposed to the outer surface in the form of concave and convex portions.

The step (1) may be carried out by immersing the stainless base material in a selective etching solution at a temperature of 30 ° C to 100 ° C for 2 to 60 minutes to selectively etch the surface of the stainless base material, more preferably at a temperature of 70 ° C to 80 ° C It may be selectively etched by immersing in the selective etching solution for 20 to 40 minutes. If the temperature at which the step (1) is performed is less than 30 ° C. or the immersion time is less than 2 minutes, it takes a long time for the reaction to take place and the chemical reaction for forming an oxide film on chromium may not proceed sufficiently, If the temperature exceeds 100 DEG C or the immersion time is 60 minutes, non-uniformity of the solution due to evaporation of water may be caused and the surface of the oxide film may be uneven.

The selective etchant may be selected from the group consisting of 25 to 200 parts by weight of polycarboxylic acid, 50 to 200 parts by weight of hydrogen peroxide, 25 to 200 parts by weight of gluconic acid, 15 to 100 parts by weight of oxalic acid, 5 to 50 parts by weight of a surfactant and water. More preferably, 40 to 160 parts by weight of a perchloric acid, 70 to 160 parts by weight of hydrogen peroxide, 50 to 150 parts by weight of gluconic acid, 30 to 80 parts by weight of oxalic acid and 10 to 25 parts by weight of a surfactant and water are added to 100 parts by weight of nitric acid, .

The nitric acid serves to oxidize corrosion-causing metals such as iron, nickel, or copper on the surface of the stainless steel base material, and may be included in an amount of 10 to 20% by weight based on the total weight of the selective etching solution. If nitric acid is contained in an amount of less than 10% by weight of the total weight of the selective etching solution, iron or nickel or other metals which cause corrosion on the surface of the stainless steel base material are not sufficiently ionized, so that the content of chromium on the surface of the stainless steel base material is relatively reduced, An oxide film may not be formed as much as desired. Also, if the acid contains more than 20% by weight of the total weight of the selective etching solution, the content of the composition of the selective etching solution such as Piclal may be reduced and the selective etching efficiency may be deteriorated. Further, There may arise a problem that an oxide film of chromium can not be sufficiently formed.

The Picallal is a mixture of picric acid and alcohol and dissolves ions of metal such as iron, nickel, or copper oxidized by the nitric acid. If the content of the above-mentioned polycarboxylic acid is less than 25 parts by weight with respect to 100 parts by weight of nitric acid, dissolution of the metal ions oxidized by nitric acid does not occur sufficiently, and the surface of the stainless steel base material remains impurities, have. If the content of the above-mentioned polycarboxylic acid exceeds 200 parts by weight with respect to 100 parts by weight of nitric acid, the polycarboxylic acid floats as an impurity after accelerating the dissolution of metal ions, and the uniformity and glossiness of the surface of the stainless- There may be a problem of degradation.

In addition, the hydrogen peroxide functions as a catalyst for oxidizing metal ions and serves to buffer decomposition. If the hydrogen peroxide is contained in an amount of less than 25 parts by weight based on 100 parts by weight of the nitric acid, oxidation of the metal ions does not sufficiently take place, and even if oxidation is carried out, the uniformity is lowered so that impurities are left on the surface of the stainless steel base material . In addition, if the hydrogen peroxide exceeds 200 parts by weight based on 100 parts by weight of the nitric acid, the content of the other composition of the selective etching solution may be relatively decreased, and the removal of the target metal may not be easy.

Also, the gluconic acid accelerates the erosion of chromium grain boundaries to facilitate the activity of the oxide film on the surface, and the oxalic acid plays a role of accelerating the oxidation of two carboxyl groups. If the gluconic acid, oxalic acid, When the weight of the activator has a weight part other than the above-mentioned range, oxidation is not sufficiently carried out and there is a limitation in forming a uniform oxide film, and the electrode potential value after the surface treatment may be lowered.

Through the selective etching of step (1), the stainless steel base material can remove the second component that may cause corrosion by pitting on the surface of the base metal, and can induce exposure of the first component that has not been removed. That is, the weight percentage of the first component included in the surface of the stainless steel base material subjected to the step (1) may be greater than the weight percentage of the first component contained in the stainless base metal. At this time, the surface portion of the stainless steel base material refers to the regions A and A 'shown in FIGS. 2A and 2 and may be a region within 0.01 μm from the surface layer. For example, as in the following embodiments, the weight percentage of chromium, which is the first component of all the metal components included in the surface portion of the stainless steel base material through the selective etching of the step (1), of the entire metal components contained in the stainless base metal It may have a value larger than the weight% of chromium which is one component. This makes it possible to form the chromium oxide film more uniformly and thickly in passivation treatment to be described later, so that the corrosion resistance and gloss of the stainless steel can be greatly improved.

Next, in the step (2) of the present invention, the step of electrolytically polishing the selectively etched stainless base material by treating the electrolytic polishing liquid is performed. The electrolytic polishing step is a step of removing the surface irregularities by anodic oxidation and imparting luster. More specifically, since the current is concentrated on the convex portions of the irregularities of the selectively etched stainless steel base material, the surface roughness is lowered, Can be improved. (See A 'in FIG. 2B and A' 'in FIG. 3)

For this purpose, the stainless steel base material may be immersed in an electrolytic polishing solution at a temperature of 30 ° C. to 120 ° C. and a current density of 5 to 90 ASD (A / dm ² ) for 10 to 500 seconds, It is possible to perform electrolytic polishing by immersing in an electrolytic polishing solution for 120 to 210 seconds at a current density of 10 to 20 ASD (A / dm ² ).

If the electrolytic polishing temperature is less than 30 ° C, a fringing phenomenon may occur due to oxygen gas generated during electrolysis. When the electrolytic polishing temperature exceeds 120 ° C, excellent luster can be obtained. However, There are restrictions that can not be controlled.

If the current density is less than 5 A / dm ² , there is a possibility that the appearance gloss of the surface of the stainless steel base material is lowered, and the gloss and blurring phenomenon repeatedly appear at the corners and center portions of the surface of the stainless steel base material, The uniformity may also be lowered.

If the immersion time is less than 10 seconds, the surface irregularities may not be sufficiently reduced and the surface roughness may not be lowered as desired. If the immersion time exceeds 500 seconds, There is a disadvantage that it is not economical compared to the effect obtained by the increase of the cost.

The electrolytic polishing solution may contain 200 to 350 parts by weight of phosphoric acid, 0.5 to 25 parts by weight of a surfactant and water per 100 parts by weight of sulfuric acid, more preferably 260 to 300 parts by weight per 100 parts by weight of sulfuric acid. Parts by weight of phosphoric acid, and 2 to 20 parts by weight of a surfactant.

The sulfuric acid serves to lower the surface roughness by removing metal irregularities on the surface of the stainless steel base material in addition to phosphoric acid. The sulfuric acid may be contained in an amount of 40 to 50% by weight based on the total weight of the electrolytic polishing solution. If sulfuric acid is contained in the electrolytic polishing solution in an amount of less than 40% by weight or phosphoric acid is contained in an amount of less than 200 parts by weight based on 100 parts by weight of sulfuric acid, surface irregularities are not sufficiently removed, It can be difficult to lower. If the sulfuric acid is contained in the electrolytic polishing solution in an amount exceeding 50% by weight, local corrosion may occur and the appearance of the surface of the stainless steel base material may become coarse. If the amount of phosphoric acid exceeds 350 parts by weight based on 100 parts by weight of sulfuric acid , It may be advantageous from the viewpoint of surface unevenness removal, but there may be a problem that the surface of the stainless steel base material is inferior in glossiness.

The irregularities of the first component can be flattened on the surface of the stainless steel base material through the electrolytic polishing step of the step (2) to lower the surface roughness, and the uniformity of the formation of the oxide film in the step (3) You can contribute.

Next, as step (3) of the present invention, a step of treating the passive corrosion treatment liquid on the electrolytically polished stainless base material to form an oxide film is carried out. (Figure 4)

The step of forming the oxide film (A '' ') is a step of forming an oxide for the first component of the stainless steel base material so that an oxide film is densely formed on the surface of the stainless base material. As a result, the corrosion resistance on the surface of the stainless steel base material becomes strong, so that the corrosion resistance is remarkably improved, and the resistance to thermal discoloration becomes strong, so that the gloss of the surface can be improved. For example, when the first component is chromium, a chromium oxide coating may be formed on the surface of the stainless steel base material. That is, when the exposure of the chromium component to the surface of the stainless steel base material is maximized through the selective etching and electrolytic polishing steps of the above steps (1) and (2), the passivation solution of step (3) is treated to form a dense chromium oxide film Can be formed.

For this purpose, the stainless base material can be immersed in the passive processing solution for 5 to 40 minutes at a temperature of 30 ° C to 90 ° C. If the immersion time for the passivation solution is less than 5 minutes, the oxidation film may not be formed densely. If the immersion time exceeds 40 minutes, it may be easy to form a dense oxidation film, but it may be disadvantageous for making the oxidation film thinner .

The passivation solution may contain 30 to 200 parts by weight of hydrogen peroxide, 15 to 100 parts by weight of citric acid, 100 to 250 parts by weight of water, and 0.3 to 25 surfactants per 100 parts by weight of nitric acid, Per 100 parts by weight of water, 50 to 160 parts by weight of hydrogen peroxide, 25 to 85 parts by weight of citric acid, 120 to 200 parts by weight of water and 1 to 15 surfactants.

The nitric acid serves to oxidize chromium and can be contained in an amount of 20 to 30% by weight based on the total weight of the passive treatment liquid. If the nitric acid is contained in an amount of less than 20% by weight based on the total weight of the passive processing solution, non-uniform oxidation to chromium exposed on the surface of the stainless base material proceeds, which may be disadvantageous for forming a dense oxide film. , The chromium may be completely oxidized and the surface of the stainless steel base material may be damaged due to the remaining nitric acid.

The hydrogen peroxide serves to provide oxygen in the oxidation reaction of chromium due to intrinsic self-decomposition reaction. If the hydrogen peroxide is contained in the passive treatment solution in an amount of less than 25 parts by weight based on 100 parts by weight of nitric acid, the electrode potential lowers, The thickness may be lowered, and the corrosion resistance may be deteriorated.

As described above, the surface treatment method of stainless steel according to the present invention is a method for selectively removing the corrosion-causing substance on the surface of the stainless steel base material through the steps (1) to (3) It is possible to obtain a stainless steel exhibiting excellent surface luster, corrosion resistance and high temperature discoloration resistance.

Further, the present invention provides a stainless steel including an oxide film for the first component formed on the surface of the stainless steel base material, and having a surface roughness (Ra) of 0.07 탆 or less.

The stainless steel may have an Ra of less than 0.7 m, an Rq of less than 0.09 m and an Rz value of less than 0.51 m through the above-described selective etching step, electrolytic polishing step and passivation step, . For example, the stainless steel may have a gloss of more than 1000 GU (Gloss Unit) at 20 °, more than 600 GU at 60 °, and a gloss of more than 100 GU at 85 °.

In addition, the stainless steel exhibits excellent corrosion resistance due to a dense oxide film formed on the surface, and may have a corrosion potential (Ecorr) of 360 mV or more, for example.

Hereinafter, the present invention will be described in more detail with reference to the following examples. The following examples are provided to illustrate the present invention, but the scope of the present invention is not limited by the following examples.

[ Example  One]

Austenic stainless steel base material having 0.1% carbon, 14.8% nickel, 16.9% chromium, 0.9% manganese, 0.4% silicon and 66.9% iron was mixed with 20 wt% nitric acid, 15 wt% , 5% by weight of sodium gluconate, 5% by weight of oxalic acid, and 2% by weight of a surfactant was immersed in a selective etching solution at a temperature of 70 캜 for 20 minutes to selectively etch the resultant.

Next, the selectively etched stainless steel base material was immersed in an electrolytic polishing solution containing 45 wt% sulfuric acid, 45 wt% phosphoric acid, 7 wt% water, and 3 wt% of surfactant at a current density of 20 A / dm ² And 75 Lt; 0 > C for about 150 seconds to perform electrolytic polishing.

Thereafter, the electrolytically polished stainless base material was immersed in a passivation solution containing 25 wt% of nitric acid, 25 wt% of hydrogen peroxide, 10 wt% of citric acid, 39 wt% of water and 1 wt% of a surfactant, For 10 minutes to perform passivation treatment.

[ Example  2 to 10]

The composition of the selective etching solution was changed as shown in Table 1, and the same procedure as in Example 1 was carried out.

[ Comparative Example  One]

The same process as in Example 1 was carried out except that selective etching was not performed.

division Selective etching solution composition (% by weight) nitric acid Pechral Hydrogen peroxide Gluconic acid Oxalic acid Surfactants water Example 1 18 18 18 18 5 2 21 Example 2 9 17 17 17 8 4 28 Example 3 23 15 15 15 5 2 25 Example 4 18 8 18 18 5 2 31 Example 5 12 26 12 12 5 2 31 Example 6 18 18 8 18 5 2 31 Example 7 12 12 26 12 5 2 31 Example 8 18 18 18 8 5 2 31 Example 9 12 12 12 26 5 2 31 Example 10 18 18 18 18 2 2 24 Example 11 12 12 12 12 15 2 35

Example 1
To
Example 11 Selective Etching Content (wt.%) carbon nickel chrome manganese silicon iron 0.1 14.8 16.9 0.9 0.4 66.9 division Content after selective etching (% by weight) carbon nickel chrome manganese silicon iron Example 1 0.14 11.2 32.5 0.76 0.9 54.5 Example 2 0.15 12.3 26.6 0.77 0.78 59.4 Example 3 0.18 13.2 25.4 0.74 0.88 59.6 Example 4 0.19 12.8 27.2 0.71 0.78 58.32 Example 5 0.21 12.1 27.4 0.74 0.79 58.76 Example 6 0.21 12.8 26.8 0.75 0.78 58.66 Example 7 0.19 13.1 26.7 0.76 0.8 58.45 Example 8 0.18 13.1 25.1 0.77 0.82 60.03 Example 9 0.19 12.5 26.1 0.74 0.83 59.64 Example 10 0.22 11.8 24.8 0.73 0.84 61.61 Example 11 0.23 13.5 24.1 0.77 0.85 60.55 * Stainless steel surface based on 15nm

Referring to Tables 1 and 2, in the case of Example 1 in which the selective etching solution according to the step (1) satisfies the numerical ranges of the present invention, any one of the compositions of the selective etching solutions does not satisfy the numerical range of the present invention It can be seen that the content of chromium is up to 35% at the 15 nm of the comparative stainless steel surface of Examples 2 to 11 which can not be obtained. That is, when a selective etching solution satisfying the numerical range of the present invention is used, the corrosion-causing substances such as iron and nickel are removed, and at the same time, the content of chromium on the surface of the stainless steel is increased so that more chromium oxide is densely It is possible to provide stainless steel exhibiting excellent surface luster, corrosion resistance and high temperature discoloration resistance.

[ Experimental Example  1] gloss evaluation

The gloss of the stainless steel base material prepared in Examples 1 to 11 and Comparative Example 1 was measured at incidence angles of 20 °, 60 ° and 85 ° using a measuring instrument (NIPPON DENSHOKU / PG-1M).

division 20 ° 60 ° 85 ° Example 1 1059 652 113.1 Example 2 898.2 514.3 101.5 Example 3 842.3 489.4 99.4 Example 4 746.4 433.6 97.7 Example 5 812.3 470.6 98.3 Example 6 784.5 452.7 97.9 Example 7 847.4 490.5 99.6 Example 8 792.6 456.4 98.1 Example 9 724.6 415.8 96.5 Example 10 759.4 440.2 96.8 Example 11 811.3 469.4 98.3 Comparative Example 1 112.9 132.9 94.5

Referring to Table 3, in the case of Example 1 in which the selective etching solution according to the step (1) satisfies all the numerical ranges of the present invention, in the case where any of the compositions of the selective etching solutions does not satisfy the numerical range of the present invention 2 to 11 shows excellent glossiness. That is, when a selective etching solution satisfying the numerical range of the present invention is used, it can have a gloss of more than 1000 GU (Gloss Unit) at 20 °, a gloss of 600 GU or more at 60 °, Or more. Furthermore, it exhibits a glossiness of 900% or more higher than that of Comparative Example 1 in which the selective etching step is not performed. Thus, it is possible to greatly improve the utilization in an industrial group in which the quality of the sensibility of the appearance is important, such as a muffler for motor vehicles or a tail trim.

[ Experimental Example  2] Surface roughness evaluation

Surface roughness was measured before performing each of the selective etching step, the electrolytic polishing step and the passivation step of Example 1 and Comparative Example 1, and is shown in Table 4 below.

Example 1 Surface roughness Early Selective Etching + Electrolytic Polishing Passive processing Ra 0.888 0.072 0.066 Rq 0.119 0.093 0.087 Rz 0.784 0.511 0.5 Comparative Example 1 Surface roughness Early Electrolytic polishing Passive processing Ra 0.888 0.113 0.105 Rq 0.119 0.175 0.164 Rz 0.784 0.603 0.619

Referring to Table 4, in the case of Example 1 in which the selective etching step was performed before the electrolytic polishing step, the surface roughness value was significantly lower than that of Comparative Example 1 in which the electrolytic polishing step was performed without performing the selective etching step . That is, by performing the selective etching step, the degree of polishing is increased by concentrating the electric current on the surface irregularities of the stainless steel base material, so that it can be seen that the surface roughness is greatly reduced even after the passivation step. As a result, it is possible to easily control defects such as lightness and blurring appearing repeatedly at the corners and center portions of the stainless steel base material surface, high gloss due to low surface roughness and gloss uniformity can be improved .

[ Experimental Example  3] Corrosion potential and corrosion current measurement

The corrosion potential and corrosion current of the stainless steel base material prepared in Examples 1 to 11 and Comparative Example 1 were measured using an AMETEK / VersaStudio V4 measuring device and are shown in Table 5 below.

division Corrosion potential (mV) Corrosion current (mA) Example 1 363.493 -85.332 Example 2 248.95 -184.75 Example 3 210.48 -194.24 Example 4 194.85 -228.65 Example 5 208.47 -190.87 Example 6 199.49 -213.15 Example 7 204.38 -197.52 Example 8 242.54 -182.46 Example 9 192.45 -214.91 Example 10 219.48 -194.28 Example 11 234.31 -189.40 Comparative Example 1 -67.465 -410.21 * Measuring conditions (potentio dynamic mode)
Step height: 2 mV
Step time: 0.2 sec
Scan rate (mV / sec): 10

Further, referring to Table 5, in the case of Example 1 in which the selective etching solution according to the step (1) satisfies the numerical range of the present invention, any one of the compositions of the selective etching solution does not satisfy the numerical range of the present invention It shows corrosion potentials up to 190% higher than those of Examples 2 to 11 and corrosion currents up to about 100 mA higher than those of Examples 2 to 11, showing remarkably excellent corrosion resistance. In particular, Example 1, which performed the selective etching step compared to Comparative Example 1 in which the selective etching step was not performed, exhibited a higher corrosion potential of about 430 mV and a corrosion current of about 325 mA, , It can be seen that the corrosion resistance can be remarkably improved by removing the weak iron and nickel from the surface of the stainless steel base material and increasing the content of chromium having a relatively high corrosion resistance.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (13)

(1) selectively etching the first component and the second component contained in the surface portion of the stainless steel base material;
(2) electrolytically polishing the selectively etched stainless base material by treating the electrolytic polishing solution; And
(3) treating the electrolytically polished stainless base material with a passivation solution to form an oxide film; Wherein the surface of the stainless steel is excellent in corrosion resistance and gloss. The method of claim 1, wherein the step (1)
And treating the stainless steel base material with a selective etching solution to remove the second component. The method according to claim 1,
Wherein the second component is more susceptible to oxidation than the first component. The method according to claim 1,
Wherein the first component comprises chromium,
Wherein the second component comprises at least one of iron, nickel, and copper. 3. The method of claim 2,
Wherein the selective etchant comprises 25 to 200 parts by weight of a perchloric acid, 50 to 200 parts by weight of hydrogen peroxide, 25 to 200 parts by weight of gluconic acid, 15 to 100 parts by weight of oxalic acid, and 5 to 50 parts by weight of a surfactant, based on 100 parts by weight of nitric acid Method of surface treatment of stainless steel. The method of claim 2, wherein the step (1)
Wherein the stainless steel base material is treated with the selective etching solution at a temperature of 30 DEG C to 100 DEG C for 2 to 60 minutes. The method according to claim 1,
Wherein the weight percentage of the first component included in the surface of the stainless steel base material subjected to the step (1) is greater than the weight percentage of the first component contained in the stainless base metal. The method according to claim 1,
Wherein the electrolytic polishing liquid contains 200 to 350 parts by weight of phosphoric acid and 0.5 to 25 parts by weight of a surfactant based on 100 parts by weight of sulfuric acid. 9. The method of claim 8,
Wherein said stainless base material is treated with said electrolytic polishing solution for 10 to 500 seconds at a temperature of 30 ° C to 120 ° C and a current density of 5 to 90 A / dm ² . The method according to claim 1,
Wherein the passive treatment liquid comprises 30 to 200 parts by weight of hydrogen peroxide, 15 to 100 parts by weight of citric acid, 100 to 250 parts by weight of water and 0.3 to 25 surfactants per 100 parts by weight of nitric acid. A stainless steel comprising an oxide film for a first component formed on a surface of a stainless steel base material and having a surface roughness (Ra) of 0.07 탆 or less. 12. The method of claim 11,
Wherein the stainless steel has a corrosion potential (Ecorr) of 360 mV or more. 12. The method of claim 11,
The stainless steel has a gloss of more than 1000 GU at 20 °, a gloss of more than 600 GU at 60 °, and a gloss of more than 100 GU at 85 °.

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