A Metallographic Corrosion Method for Super Ferritic Stainless Steel

Abstract

A metallographic corrosion method for super ferritic stainless steel belongs to the field of heat treatment. The metallographic etchant used in the corrosion method is an oxalic acid aqueous solution or an oxalic acid-citric acid aqueous solution, and the corrosion method is electrolytic corrosion. By mass percentage, in the oxalic acid aqueous solution, oxalic acid is 8-12%, and the balance is water; part of the oxalic acid is replaced by citric acid to form an oxalic acid-citric acid aqueous solution. The specific corrosion method is as follows: After the metallographic specimen is conventionally ground and polished, it serves as the anode, and an austenitic stainless steel plate serves as the cathode. After being immersed in the metallographic etchant, it is electrically corroded. The raw materials of the metallographic etchant used are widely sourced, simple to prepare, and low in cost. The corrosion method is convenient to operate, precisely controllable, and has good reproducibility. The surface of the specimen is clean and tidy, and the corrosion effect is stable and reliable. It can quickly, uniformly, clearly, and completely display the metallographic structure characteristics of super ferritic stainless steel at room temperature, providing support for formulating the heat treatment system and guaranteeing the production, research and development, promotion and application of this type of steel.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat treatment, and particularly relates to a metallographic corrosion method for super ferritic stainless steel. Background Art

[0002] Due to its extremely excellent comprehensive properties such as resistance to chloride pitting corrosion and stress corrosion, and low cost, super ferritic stainless steel can be used as a substitute material for expensive alloys such as super austenitic stainless steel, titanium alloy, and Hastelloy alloy, and can be widely applied in harsh corrosion environments such as coastal power plant condensers, seawater desalination, and chlor-alkali industry, having broad application prospects and potential commercial value.

[0003] The mechanical properties and corrosion resistance of metal materials are often determined by their microstructures, and a reasonable heat treatment process system is an important means to ensure that the material obtains excellent microstructures. Therefore, the observation of microstructures and the accurate evaluation of grain sizes are particularly important. An appropriate corrosion method is the key to obtaining metallographic microstructures. Super ferritic stainless steel contains extremely high Cr (26 - 30 wt%) and Mo (1 - 4 wt%), and a dense and corrosion-resistant passivation film will form on the surface of the stainless steel, resulting in extremely excellent corrosion resistance. It is difficult to clearly and completely display the microstructures, and conventional corrosion agents have many disadvantages such as complex composition, high cost, cumbersome preparation process, easy deterioration, high safety hazards, and non-reusability.

[0004] Therefore, there is an urgent need to provide a corrosion method for super ferritic stainless steel with simple preparation of corrosion agent, convenient operation of corrosion method, stable and reliable corrosion effect, so as to provide technical support for formulating a reasonable heat treatment system, and further provide a solid technical guarantee for the production, research and development, popularization and application of this type of steel. Summary of the Invention

[0005] Aiming at the above deficiencies of the prior art, the present invention aims to provide a metallographic corrosion method for super ferritic stainless steel, which has wide sources of raw materials for metallographic corrosion agent, simple preparation, low cost, convenient operation, accurate control, good reproducibility, clean and tidy sample surface, stable and reliable corrosion effect, can quickly, uniformly, clearly and completely display the metallographic tissue characteristics of super ferritic stainless steel at room temperature, provides technical support for formulating a reasonable heat treatment system, and further provides a solid guarantee for the production, research and development, popularization and application of this type of steel, having good economic benefits and application and popularization value.

[0006] To achieve the above invention purpose, the present invention is realized through the following technical solutions:

[0007] A metallographic etching method for a super ferritic stainless steel of the present invention uses an oxalic acid aqueous solution as the metallographic etchant. By mass percentage, oxalic acid is 8-12%, and the balance is water; the etching method is electrolytic etching.

[0008] Part of the oxalic acid can also be replaced by citric acid. Preferably, the metallographic etchant is an oxalic acid-citric acid aqueous solution. By mass percentage, oxalic acid is 5-6%, citric acid is 3-6%, and the balance is water.

[0009] A metallographic etching method for a super ferritic stainless steel of the present invention specifically includes the following steps:

[0010] (1) Sample pretreatment

[0011] Cut a metallographic specimen from a hot-rolled sheet of super ferritic stainless steel, grind, polish, clean, and dry the surface to be measured of the specimen to obtain a specimen to be etched.

[0012] (2) Electrolytic etching

[0013] Use the surface to be etched of the specimen to be etched as the anode, connect it to the positive pole of the DC power supply, use an austenitic stainless steel plate as the cathode, connect it to the negative pole of the DC power supply, immerse the anode and cathode in the metallographic etchant of the super ferritic stainless steel, and keep them parallel and opposite; energize for etching, control the voltage at 2.5-4V, control the current at 0.12-0.18A, and the time at 35-60s. Cut off the power supply, take out the specimen, first rinse it with clean water, then rinse it with anhydrous ethanol and dry it with hot air to obtain the metallographic etching sample of the super ferritic stainless steel.

[0014] In the step (1) described above, the cutting is carried out by using a wire electrical discharge machining equipment.

[0015] In the step (1) described above, the size of the metallographic specimen of the super ferritic stainless steel is 10×8×4mm.

[0016] In the step (1) described above, the grinding is to roughly grind and finely grind the surface to be measured of the specimen with 240#, 400#, 600#, 800#, 1000#, and 2000# SiC sandpapers; the polishing is to polish it with 2.5μm polishing paste on a polishing cloth until the surface is bright and free of scratches; the cleaning is to rinse with clean water and anhydrous ethanol; the drying is to blow dry.

[0017] The beneficial effects of the present invention are:

[0018] A metallographic etching method for a super ferritic stainless steel provided by the present invention effectively solves the technical problem that it is difficult to etch out its microstructure due to its strong corrosion resistance. Due to the adoption of the above technical solution, the present invention has the following technical effects:

[0019] (1) The raw materials of the metallographic etchant are widely sourced, easy to prepare, and low in cost;

[0020] (2) The etching method is convenient to operate, safe, efficient, precise, and controllable;

[0021] (3) The etching effect is stable, reliable, reproducible, clear, and neat. Description of the Drawings

[0022] Figure 1 The metallographic photograph of the hot-rolled sample obtained in Example 1, with a magnification of 100 times.

[0023] Figure 2 The metallographic photograph of the annealed sample obtained in Example 2 by annealing at 975 °C for 3 min, with a magnification of 100 times.

[0024] Figure 3 The metallographic photograph of the annealed sample obtained in Example 3 by annealing at 975 °C for 5 min, with a magnification of 100 times.

[0025] Figure 4 The metallographic photograph of the annealed sample obtained in Example 4 by annealing at 975 °C for 5 min, with a magnification of 100 times.

[0026] Figure 5 The metallographic photograph of the annealed sample obtained in Comparative Example 1 by annealing at 975 °C for 5 min, with a magnification of 100 times.

[0027] Figure 6 The metallographic photograph of the annealed sample obtained in Comparative Example 2 by annealing at 975 °C for 5 min, with a magnification of 100 times.

[0028] Figure 7 The metallographic photograph of the annealed sample obtained in Comparative Example 3 by annealing at 975 °C for 5 min, with a magnification of 100 times. Detailed Embodiments

[0029] To make the technical solutions and advantages of the embodiments of the present invention clearer, the following will be described in detail and completely in combination with specific implementation cases and drawings.

[0030] The metallographic etching method provided by the present invention is applicable to super ferritic stainless steel with strong corrosion resistance, and its chemical components and mass percentages are: Cr: 26 - 30%, Mo: 1 - 4%, C + N ≤ 0.01%, S ≤ 0.006%, P ≤ 0.006%, and the balance is Fe. In the following examples, hot-rolled and different annealed super ferritic stainless steel samples are used to illustrate the metallographic etching method and etching effect provided by the present invention.

[0031] Example 1

[0032] In this embodiment, hot-rolled super ferritic stainless steel is used as a metallographic sample, and a metallographic corrosion method of super ferritic stainless steel provided by the present invention is adopted, and the specific steps are as follows:

[0033] (1) Sample pretreatment

[0034] The sample with the size of 10 mm in length × 8 mm in width × 4 mm in thickness was cut from the hot-rolled super ferritic stainless steel plate by using electric spark wire cutting equipment. The test surface of the sample was coarsely and finely ground by using 240#, 400#, 600#, 800#, 1000# and 2000# SiC sandpaper, and then polished by using 2.5 μm polishing paste on the polishing cloth until the surface was bright and scratch-free, and then rinsed with clean water and anhydrous ethanol and blown dry.

[0035] (2) Preparation of metallographic etchant

[0036] Mix according to the mass percentage, oxalic acid: deionized water = 10:90, add oxalic acid into deionized water, and stir continuously with a glass rod until the oxalic acid is completely dissolved to prepare a 10% oxalic acid aqueous solution;

[0037] (3) Electrolytic corrosion

[0038] The surface of the sample to be corroded is used as the anode, connected to the positive electrode of the DC power supply, and the austenitic stainless steel plate is used as the cathode, connected to the negative electrode of the DC power supply. The anode and cathode need to be immersed in the metallographic corrosive agent and kept parallel and opposite to each other; power on for corrosion, control the voltage at 3.6V, the current at 0.17A, and the time at 35s; cut off the power supply, take out the sample, rinse it with water first, then rinse it with anhydrous ethanol and blow it dry with hot air;

[0039] (4) Organizational Observation

[0040] The microstructure of the hot-rolled sample was observed using a Zeiss observer.Zlm Zeiss metallographic microscope. Figure 1 As shown, it can clearly and completely reflect the microstructure of the hot-rolled sample, which is composed of a large number of banded crystals and a small amount of equiaxed crystals, showing typical hot-rolled organizational characteristics.

[0041] From the test results of this embodiment, it can be seen that the corrosion method provided by the present invention is suitable for the preparation of hot-rolled super ferrite stainless steel metallographic specimens by corrosion.

[0042] Example 2

[0043] In this embodiment, super ferrite stainless steel annealed at 975°C for 3 minutes is used as a metallographic sample, and a metallographic corrosion method for super ferrite stainless steel provided by the present invention is adopted, and the specific steps are as follows:

[0044] (1) Sample pretreatment

[0045] Samples with dimensions of 10 mm in length, 8 mm in width and 4 mm in thickness were cut from annealed super ferritic stainless steel sheets using a wire electrical discharge machining equipment. The surfaces to be measured of the samples were coarsely and finely ground using 240#, 400#, 600#, 800#, 1000# and 2000# SiC sandpapers, and then polished using 2.5 μm polishing paste on a polishing cloth until the surface was bright and free of scratches. They were rinsed with clean water and anhydrous ethanol and dried with air;

[0046] (2) Preparation of metallographic etchant

[0047] Mixing by mass percentage, oxalic acid: deionized water = 10:90. Add oxalic acid to deionized water and continuously stir with a glass rod until the oxalic acid is completely dissolved to prepare a 10% oxalic acid aqueous solution;

[0048] (3) Electrolytic etching

[0049] Using the surface to be etched of the sample as the anode, connected to the positive pole of the DC power supply, and using an austenitic stainless steel plate as the cathode, connected to the negative pole of the DC power supply. The anode and cathode need to be immersed in the metallographic etchant and kept parallel and opposite; conduct etching by energizing, control the voltage at 3.1 V, the current at 0.12 A, and the time at 55 s; cut off the power supply, take out the sample, first rinse with clean water, then rinse with anhydrous ethanol and dry with hot air;

[0050] (4) Microstructure observation

[0051] The microstructure of the annealed sample was observed using a Zeiss observer.Zlm type metallographic microscope. As Figure 2 shown, it can clearly and completely reflect the microstructure of the annealed sample, which is composed of a large number of equiaxed grains and a small amount of banded grains, showing the characteristics of incomplete recrystallization.

[0052] From the test results of this example, the etching method provided by the present invention is applicable to the preparation of metallographic etched samples of incompletely recrystallized annealed super ferritic stainless steel.

[0053] Example 3

[0054] In this example, the annealed super ferritic stainless steel at 975 °C for 5 min was used as the metallographic sample, and a metallographic etching method for super ferritic stainless steel provided by the present invention was adopted. The specific steps are as follows:

[0055] (1) Sample pretreatment

[0056] Samples with dimensions of 10 mm in length, 8 mm in width, and 4 mm in thickness were cut from hot-rolled super ferritic stainless steel plates using a wire electrical discharge machining equipment. The surfaces to be measured of the samples were rough-ground and fine-ground using 240#, 400#, 600#, 800#, 1000#, and 2000# SiC sandpapers, and then polished using 2.5 μm polishing paste on a polishing cloth until the surfaces were bright and scratch-free. They were rinsed with clean water and anhydrous ethanol and dried with air;

[0057] (2) Preparation of metallographic etchant

[0058] Mixing by mass percentage, oxalic acid: deionized water = 10:90. Add oxalic acid to deionized water and continuously stir with a glass rod until the oxalic acid is completely dissolved to prepare a 10% oxalic acid aqueous solution;

[0059] (3) Electrolytic etching

[0060] Using the surface to be etched of the sample as the anode, connected to the positive pole of the DC power supply, and using an austenitic stainless steel plate as the cathode, connected to the negative pole of the DC power supply. The anode and cathode need to be immersed in the metallographic etchant and kept parallel and opposite to each other; conduct etching by applying electricity, control the voltage at 3.3 V, the current at 0.14 A, and the time at 45 s; cut off the power supply, take out the sample, first rinse it with clean water, then rinse it with anhydrous ethanol and dry it with hot air;

[0061] (4) Microstructure observation

[0062] The microstructure of the annealed sample was observed using a Zeiss observer.Zlm type metallographic microscope. As Figure 3 shown, it can clearly and completely reflect the microstructure of the annealed sample, which consists of equiaxed grains and exhibits the characteristics of complete recrystallization.

[0063] From the test results of this example, the etching method provided by the present invention is applicable to the preparation of metallographic etched samples of fully recrystallized annealed super ferritic stainless steel.

[0064] Example 4

[0065] In the example, the super ferritic stainless steel annealed at 975 °C for 5 min was used as the metallographic sample, and an oxalic acid-citric acid aqueous solution was used as the metallographic etchant. The specific steps are as follows:

[0066] (1) Sample pretreatment

[0067] A sample with dimensions of 10 mm in length, 8 mm in width, and 4 mm in thickness was cut from a hot-rolled super ferritic stainless steel sheet using a wire electrical discharge machining equipment. The surface to be measured of the sample was coarsely and finely ground using 240#, 400#, 600#, 800#, 1000#, and 2000# SiC sandpapers, and then polished using 2.5 μm polishing paste on a polishing cloth until the surface was bright and free of scratches. It was rinsed with clean water and anhydrous ethanol and dried with a blower;

[0068] (2) Preparation of metallographic etching agent

[0069] Mix according to mass percentage, oxalic acid: citric acid: deionized water = 5:5:90. Add oxalic acid and citric acid to deionized water and continuously stir with a glass rod until oxalic acid and citric acid are completely dissolved to prepare a mixed solution of oxalic acid, citric acid, and deionized water;

[0070] (3) Electrolytic etching

[0071] Using the surface to be etched of the sample as the anode, connect it to the positive pole of the DC power supply, use an austenitic stainless steel plate as the cathode, connect it to the negative pole of the DC power supply. The anode and cathode need to be immersed in the metallographic etching agent and kept parallel and opposite; conduct etching by energizing, control the voltage at 3.2 V, the current at 0.12 A, and the time at 45 s; cut off the power supply, take out the sample, first rinse it with clean water, then rinse it with anhydrous ethanol and dry it with hot air;

[0072] (4) Microstructure observation

[0073] The microstructure of the annealed sample was observed using a Zeiss observer.Zlm type metallographic microscope. As Figure 4 shown, it can clearly and completely reflect the microstructure of the annealed sample, which is composed of equiaxed grains and shows the characteristics of complete recrystallization.

[0074] From the test results of this comparative example, the metallographic etching method using citric acid to replace part of oxalic acid has the same effect as the metallographic etching method provided by the present invention and is also applicable to the preparation of super ferritic stainless steel metallographic etched samples.

[0075] Comparative Example 1

[0076] In this example, the super ferritic stainless steel annealed at 975 °C for 5 min was used as the metallographic sample, and aqua regia solution was used as the metallographic etching agent for chemical etching. The specific steps are as follows:

[0077] (1) Sample pretreatment

[0078] Samples with dimensions of 10 mm in length × 8 mm in width × 4 mm in thickness were cut from hot-rolled super ferritic stainless steel sheets using a wire electrical discharge machining equipment. The surfaces of the samples to be measured were rough-ground and fine-ground using 240#, 400#, 600#, 800#, 1000# and 2000# SiC sandpapers, and then polished using 2.5 μm polishing paste on a polishing cloth until the surfaces were bright and scratch-free. They were rinsed with clean water and anhydrous ethanol and dried with hot air;

[0079] (2) Preparation of metallographic etchant

[0080] Mixing by volume percentage, hydrochloric acid: nitric acid = 3:1. The nitric acid was slowly added to the hydrochloric acid through a glass rod and continuously stirred with the glass rod until evenly mixed to prepare aqua regia solution;

[0081] (3) Chemical etching

[0082] The samples were placed in the aqua regia solution for 2 minutes of immersion. The samples were taken out, first rinsed with clean water, then rinsed with anhydrous ethanol and dried with hot air;

[0083] (4) Microstructure observation

[0084] The microstructure of the annealed samples was observed using a Zeiss observer.Zlm type metallographic microscope. As Figure 5 shown, although a certain etching effect can be achieved using this etching method, the etched grain boundaries are not clear, showing the phenomena of uneven etching and over-etching, and there are also problems that the chemical etching time is not easy to control and the solution will become ineffective after long-term placement, which brings difficulties to the observation of the metallographic structure and the statistics of grain size.

[0085] From the test results of this comparative example, the effect of chemical etching using aqua regia solution is far inferior to that of the metallographic etching method provided by the present invention and is not suitable for the preparation of metallographic etched samples of super ferritic stainless steel.

[0086] Comparative Example 2

[0087] In this example, super ferritic stainless steel annealed at 975 °C for 5 minutes was used as the metallographic sample, and chemical etching was carried out using a copper sulfate-hydrochloric acid aqueous solution. The specific steps are as follows:

[0088] (1) Sample pretreatment

[0089] Samples with dimensions of 10 mm in length, 8 mm in width, and 4 mm in thickness were cut from hot-rolled super-ferritic stainless steel plates using a wire electrical discharge machining (EDM) device. The surfaces to be measured of the samples were coarsely and finely ground using 240#, 400#, 600#, 800#, 1000#, and 2000# SiC sandpapers, and then polished using a 2.5 μm polishing paste on a polishing cloth until the surface was bright and scratch-free. The samples were rinsed with clean water and anhydrous ethanol and dried with hot air;

[0090] (2) Preparation of metallographic etchant

[0091] 5 g of copper sulfate pentahydrate was added to 25 ml of deionized water and stirred with a glass rod until the copper sulfate pentahydrate was completely dissolved. Then, 25 ml of hydrochloric acid was added to the copper sulfate aqueous solution and stirred with a glass rod until evenly mixed to prepare a copper sulfate-hydrochloric acid aqueous solution;

[0092] (3) Chemical etching

[0093] The samples were placed in the copper sulfate-hydrochloric acid aqueous solution for 5 minutes of immersion. The samples were taken out, first rinsed with clean water, then rinsed with anhydrous ethanol and dried with hot air;

[0094] (4) Microstructure observation

[0095] The microstructure of the annealed samples was observed using a Zeiss observer.Zlm type metallurgical microscope. As Figure 6 shown, the grain boundaries of the super-ferritic stainless steel could not be etched using this etching method;

[0096] From the test results of this comparative example, the method of chemical etching using a copper sulfate-hydrochloric acid aqueous solution is not applicable to the preparation of metallographic-etched samples of super-ferritic stainless steel.

[0097] Comparative Example 3

[0098] In this example, super-ferritic stainless steel annealed at 975 °C for 5 minutes was used as the metallographic sample, and chemical etching was carried out using a ferric chloride-hydrochloric acid aqueous solution. The specific steps are as follows:

[0099] (1) Sample pretreatment

[0100] Samples with dimensions of 10 mm in length, 8 mm in width, and 4 mm in thickness were cut from hot-rolled super-ferritic stainless steel plates using a wire electrical discharge machining (EDM) device. The surfaces to be measured of the samples were coarsely and finely ground using 240#, 400#, 600#, 800#, 1000#, and 2000# SiC sandpapers, and then polished using a 2.5 μm polishing paste on a polishing cloth until the surface was bright and scratch-free. The samples were rinsed with clean water and anhydrous ethanol and dried with hot air;

[0101] (2) Preparation of metallographic etchant

[0102] Add 5 g of ferric chloride into 100 ml of deionized water, stir with a glass rod until the ferric chloride is completely dissolved, then add 50 ml of hydrochloric acid into the ferric chloride aqueous solution, and stir with a glass rod until evenly mixed to prepare an aqueous solution of ferric chloride and hydrochloric acid.

[0103] (3) Chemical etching

[0104] Put the specimen into the aqueous solution of ferric chloride and hydrochloric acid, soak for 5 min, take out the specimen, first rinse with clean water, then rinse with absolute ethanol and dry with hot air.

[0105] (4) Microstructure observation

[0106] Use a Zeiss observer.Zlm type Zeiss metallographic microscope to observe the microstructure of the annealed specimen. As Figure 7 shown, the grain boundaries of the super ferrite stainless steel could not be etched out by using this etching method.

[0107] From the test results of this comparative example, the method of chemical etching with an aqueous solution of ferric chloride and hydrochloric acid is not applicable to the preparation of metallographic etching specimens of super ferrite stainless steel.

[0108] The above examples illustrate that not all existing metallographic etchants can clearly and completely display the microstructure of super ferrite stainless steel. Through research, after etching with metallographic etchants (oxalic acid aqueous solution, oxalic acid-citric acid aqueous solution) with wide sources, simple preparation and low cost, the etching effect is stable and reliable, has good reproducibility, and is clear and neat.

[0109] It should be understood that the specific order or hierarchy of the steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of the steps in the process can be rearranged without departing from the protection scope of the present disclosure. The appended method claims present the elements of the various steps in an exemplary order and are not intended to be limited to the specific order or hierarchy described.

[0110] The above examples are only used to illustrate the technology provided by the present invention, so that those familiar with such technology can understand and apply the content of the present invention, and do not limit the technical solution. Any modification or equivalent replacement of the technical solution of the present invention, without departing from the scope and purpose of the present invention, should be covered within the scope of the claims required by the present invention.

Claims

1. A metallographic corrosion method for super ferritic stainless steel, characterized in that, The metallographic etching method for super ferritic stainless steel uses a metallographic etchant with the following mass percentages: oxalic acid is 5 - 6%, citric acid is 3 - 6%, and the balance is water. The etching method is electrolytic etching, including the following steps: (1) Sample pretreatment Cut a metallographic specimen from a hot-rolled sheet of super ferritic stainless steel. Grind, polish, clean, and dry the surface to be tested of the specimen to obtain the specimen to be etched. (2) Electrolytic etching Use the surface to be etched of the specimen to be etched as the anode, connected to the positive pole of the DC power supply. Use an austenitic stainless steel plate as the cathode, connected to the negative pole of the DC power supply. Immerse the anode and cathode in the metallographic etchant for super ferritic stainless steel and keep them parallel and opposite. Apply current for etching, control the voltage at 2.5 - 4V, the current at 0.12 - 0.18A, and the time at 35 - 60s. Cut off the power supply, take out the specimen, first rinse it with clean water, then rinse it with absolute ethanol and dry it with hot air to obtain the metallographic etched sample of super ferritic stainless steel.

2. The metallographic corrosion method for super ferritic stainless steel according to claim 1, characterized in that, In the step (1) described above, the cutting is carried out using a wire electrical discharge machining equipment.

3. The metallographic corrosion method for super ferritic stainless steel according to claim 1, characterized in that, In the step (1) described above, the size of the metallographic specimen of super ferritic stainless steel is 10×8×4mm.

4. The metallographic corrosion method for super ferritic stainless steel according to claim 1, characterized in that, In the step (1) described above, the grinding is to coarsely grind and finely grind the surface to be tested of the specimen using 240#, 400#, 600#, 800#, 1000#, and 2000# SiC sandpapers.

5. The metallographic corrosion method for super ferritic stainless steel according to claim 1, characterized in that, In the step (1) described above, the polishing is to polish it on a polishing cloth using 2.5μm polishing paste until the surface is bright and free of scratches.

6. The metallographic corrosion method for super ferritic stainless steel according to claim 1, characterized in that, In the step (1) described above, the cleaning is to rinse it with clean water and absolute ethanol.

7. The metallographic corrosion method for super ferritic stainless steel according to claim 1, characterized in that, In the step (1) described above, the drying is to dry it by blowing.

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