Ferrite metallographic specimen preparation method for removing surface corrosion black spots

Abstract

The invention relates to a preparation method of a ferrite metallographic specimen for removing surface corrosion black spots. The preparation method comprises the following steps: 1) grinding and polishing the specimen; 2) electrolytic polishing and electrolytic corrosion; 3) cleaning the sample; and 4) ultrasonic cleaning. According to the method, the pretreated sample is subjected to electrolytic polishing and electrolytic corrosion through an electrolytic polishing corrosion device, the surface of the sample is cleaned through ultrasonic waves after wiping and cleaning are conducted through ethyl alcohol, corrosion black spots on the surface of the ferrite metallographic sample can be effectively removed, and the problem that corrosion is difficult when the ferrite metallographic sample is prepared is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of metallographic inspection, and particularly relates to a method for preparing a ferrite metallographic specimen for removing surface corrosion black spots. Background Art

[0002] The current development trend in the automotive industry is to reduce its own weight and save energy and reduce emissions. In order to meet the requirements of automotive lightweighting, the research on high-strength automotive steels has become a hot topic. Refining the grain size is a method that can not only improve the strength of steel but also improve its formability. Fine-grained high-strength interstitial-free steel is favored because it has high strength and good deep-drawing properties. It is based on the composition of interstitial-free (IF) steel, adding solid solution strengthening elements such as Mn and Si to improve the strength of the steel plate, using unique fine precipitates to refine the grains, and producing a precipitation strengthening effect. This new type of fine-grained high-strength IF steel has become one of the steel grades that meet the requirements of automotive lightweighting due to its good deep-drawing properties, resistance to secondary processing brittleness, and coating surface quality.

[0003] IF steel has become the third-generation automotive stamping steel after rimmed steel and aluminum-killed steel due to its excellent deep-drawing properties, solving the forming problems of some difficult-to-stamp parts on automobiles. Some studies have shown that the excellent deep-drawing properties of IF steel are closely related to its strong {11l} recrystallization texture. The microstructure of conventional IF steel is ferrite. After adding high alloys to IF steel, its microstructure is still ferrite, but the ferrite grain size and texture will change. Therefore, its microstructure corrosion is different from conventional corrosion.

[0004] Conventional etchants cannot obtain the ferrite metallographic structure of high-alloy IF steel, and there are a large number of black corrosion spots on the surface of the specimen after electrolytic corrosion. Therefore, it is necessary to develop a new method for preparing δ-ferrite metallographic specimens starting from the etchant and corrosion method to solve the problem of difficult corrosion of δ-ferrite metallographic specimens. Summary of the Invention

[0005] The present invention provides a method for preparing a ferrite metallographic specimen for removing surface corrosion black spots. The pretreated specimen is subjected to electrolytic polishing and electrolytic corrosion using an electrolytic polishing and corrosion device. After wiping and cleaning with alcohol, the surface of the specimen is further cleaned by ultrasonic waves, which can effectively remove the corrosion black spots on the surface of the ferrite metallographic specimen and solve the problem of difficult corrosion during the preparation of the ferrite metallographic specimen.

[0006] To achieve the above object, the present invention is realized by adopting the following technical solutions:

[0007] A method for preparing a ferrite metallographic specimen for removing surface corrosion black spots, comprising the following steps:

[0008] 1) Grinding and polishing the specimen;

[0009] 2) Electropolishing and electrolytic etching: Use perchloric acid with a mass concentration of 10% - 15%, and perform electropolishing and electrolytic etching using an electropolishing and etching device; the voltage during electropolishing is 40 - 50 V, and the time is 5 - 10 s; the voltage during electrolytic etching is 20 - 25 V, and the time is 10 - 20 s;

[0010] 3) Clean the specimen: Wipe and clean the surface of the specimen after electrolytic etching to remove surface residues;

[0011] 4) Ultrasonic cleaning: Place the specimen in absolute ethanol for ultrasonic cleaning, wipe it, and then dry it.

[0012] In the said step 1), first coarsely grind the surface of the specimen with water sandpaper on a metallographic pre - grinding machine, and then polish the surface of the specimen using a mechanical polishing machine. The surface of the polished specimen is in a flat mirror state.

[0013] In the said step 2), the electropolishing and etching device is an electropolishing and etching instrument.

[0014] In the said step 3), wipe and clean the surface of the specimen after electrolytic etching with absorbent cotton under running water.

[0015] In the said step 4), hold the specimen with tweezers, perform ultrasonic cleaning in absolute ethanol to remove the residues after wiping with absorbent cotton, and finally take out the specimen and dry it.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] 1) Subject the pretreated specimen to electropolishing and electrolytic etching using an electropolishing and etching device, wipe and clean it with alcohol, and then perform ultrasonic cleaning on the surface of the specimen, which can effectively remove the corrosion black spots on the surface of the ferrite metallographic specimen and solve the problem of difficult corrosion during the preparation of ferrite metallographic specimens.

[0018] 2) Can quickly prepare a ferrite microstructure corrosion specimen with a clean surface, and then obtain a micro - microstructure morphology photo without black spot interference by taking pictures. Description of the Drawings

[0019] Figure 1 It is a metallographic structure photo of the comparative example of the present invention after being corroded with a nitric acid - alcohol etching solution with a mass concentration of 4% (the micro - structure of the specimen cannot be corroded out).

[0020] Figure 2 It is a metallographic structure photo of the ferrite metallographic specimen obtained after electrolytic etching with perchloric acid with a mass concentration of 10% in the comparative example of the present invention (there are a large number of corrosion black spots on the surface). Figure 3This is a metallographic structure photograph of a ferrite metallographic specimen prepared by the method described in the embodiments of the present invention (with a clean surface and clear grain boundaries). Detailed implementation manners

[0021] The method for preparing a ferrite metallographic specimen for removing surface corrosion black spots according to the present invention includes the following steps:

[0022] 1) Grinding and polishing the specimen;

[0023] 2) Electrochemical polishing and electrochemical etching: Using perchloric acid with a mass concentration of 10% - 15%, and performing electrochemical polishing and electrochemical etching by means of an electrochemical polishing and etching device; the voltage during electrochemical polishing is 40 - 50V, and the time is 5 - 10s; the voltage during electrochemical etching is 20 - 25V, and the time is 10 - 20s;

[0024] 3) Cleaning the specimen: Wiping and cleaning the surface of the specimen after electrochemical etching to remove surface residues;

[0025] 4) Ultrasonic cleaning: Placing the specimen in absolute ethanol for ultrasonic cleaning, wiping it, and then drying it.

[0026] In the step 1), first, coarsely grind the surface of the specimen with water sandpaper on a metallographic pre - grinding machine, and then polish the surface of the specimen with a mechanical polishing machine. The polished surface of the specimen is in a flat mirror state.

[0027] In the step 2), the electrochemical polishing and etching device is an electrochemical polishing and etching instrument.

[0028] In the step 3), wipe and clean the surface of the specimen after electrochemical etching with absorbent cotton under running water.

[0029] In the step 4), hold the specimen with tweezers, perform ultrasonic cleaning in absolute ethanol to remove the residues after wiping with absorbent cotton, and finally take out the specimen and dry it.

[0030] To more intuitively illustrate the present invention, the implementation manners of the present invention are further described in combination with embodiments. The following embodiments are only preferred specific implementation manners of the present invention, but the protection scope of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the technical scope disclosed by the present invention, including simple changes or equivalent replacements, are within the protection scope of the present invention.

[0031]

Embodiment

[0032] In this embodiment, a metallographic specimen of an aluminum - containing IF steel cold - rolled sheet is prepared by the method described in the present invention; in the comparative example, a metallographic specimen is prepared by a conventional electrochemical etching method.

[0033] Comparative example: The microscopic structure of the specimen could not be etched using a nitric acid alcohol etching solution with a mass concentration of 4% (as Figure 1 shown); when using perchloric acid with a mass concentration of 10%, the grain boundaries of the microscopic structure of the etched specimen were not clear, and there were a large number of black etching points on the surface of the specimen, as Figure 2 shown.

[0034] The preparation process of the metallographic specimen in this example is as follows:

[0035] 1. Grinding and polishing of the specimen: Using the method of mechanical grinding, first coarsely grind the surface of the specimen with water sandpaper on a metallographic pre-grinder, and then polish the surface of the specimen polished with sandpaper using a mechanical polishing machine. After polishing, uniformly remove the scratches left by the finest sandpaper to make the surface of the specimen reach a flat mirror state.

[0036] 2. Electropolishing and electrolytic etching: Using perchloric acid with a mass concentration of 12%, perform electropolishing and electrolytic etching on the surface of the specimen using an electropolishing and etching instrument; the voltage during electropolishing is 50V and the time is 5s; the voltage during electrolytic etching is 25V and the time is 15s.

[0037] 3. Cleaning the surface of the specimen: Wipe and clean the surface of the specimen after electrolytic etching with absorbent cotton under running water to wipe off the residues after etching.

[0038] 4. Ultrasonic cleaning: Clamp the specimen with tweezers and perform ultrasonic cleaning in anhydrous ethanol to remove the residues after wiping with absorbent cotton, and finally take out the specimen and dry it.

[0039] The metallographic specimen prepared in this example can observe a clean (almost no etching black spots) and clear grain boundary microscopic structure under the microscope, as Figure 3 shown.

[0040] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a ferritic metallographic specimen for removing surface corrosion black spots, characterized in that, It includes the following steps: 1) Grinding and polishing the specimen; 2) Electrochemical polishing and etching: Using perchloric acid with a mass concentration of 10% - 15%, and performing electrochemical polishing and etching with an electrochemical polishing and etching device; the voltage during electrochemical polishing is 40 - 50V, and the time is 5 - 10s; the voltage during electrochemical etching is 20 - 25V, and the time is 10 - 20s; 3) Cleaning the specimen: Wiping and cleaning the surface of the specimen after electrochemical etching to remove surface residues; 4) Ultrasonic cleaning: Placing the specimen in absolute ethanol for ultrasonic cleaning, wiping it, and then drying it.

2. The method for preparing a ferritic metallographic specimen for removing surface corrosion black spots according to claim 1, wherein, In step 1), first coarsely grind the surface of the specimen with water sandpaper on a metallographic pre - grinding machine, and then polish the surface of the specimen with a mechanical polishing machine. The surface of the polished specimen is in a flat mirror state.

3. A method for preparing a ferritic metallographic specimen for removing surface corrosion black spots according to claim 1, characterized in that, In step 2), the electrochemical polishing and etching device is an electrochemical polishing and etching instrument.

4. A method for preparing a ferritic metallographic specimen for removing surface corrosion black spots according to claim 1, characterized in that, In step 3), wipe and clean the surface of the specimen after electrochemical etching with absorbent cotton under running water.

5. A method for preparing a ferritic metallographic specimen for removing surface corrosion black spots according to claim 1, characterized in that, In step 4), hold the specimen with tweezers, perform ultrasonic cleaning in absolute ethanol to remove the residues after wiping with absorbent cotton, and finally take out the specimen and dry it.

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