KR20090058603A

KR20090058603A - Electrolyting method of carbon carburizing steel specimen for electron back scattered diffraction

Info

Publication number: KR20090058603A
Application number: KR1020070125222A
Authority: KR
Inventors: 이승현
Original assignee: 현대자동차주식회사
Priority date: 2007-12-05
Filing date: 2007-12-05
Publication date: 2009-06-10

Abstract

The present invention relates to an electropolishing method for carburizing steel specimens for EBSD measurement, comprising electrolytic polishing for electrolytic polishing of the surface portion of the carburizing steel specimen by adding methanol, propanol and acetic acid having excellent polishing properties, and optimal electropolishing temperature. And presenting by setting the time, and relates to the electropolishing method of the carburized steel specimens that can obtain a cleaner and superior surface quality than in the prior art. According to the electropolishing method of the present invention, it is possible to obtain a clean, deformation-free surface quality, which was impossible when using a conventional electrolytic solution for carburized steel, thereby obtaining more accurate EBSD measurement results.

Description

Electrolytic Polishing Method of Carbon Carburizing Steel Specimen for Electron Back Scattered Diffraction

The present invention relates to an electropolishing method for a carburized steel specimen for electrospheric diffraction (EBSD) analysis, and more particularly to methanol, propanol, and acetic acid having excellent polishing properties as an electrolytic solution for electropolishing the surface of the carburized steel specimen. The present invention relates to an electropolishing method of carburized steel specimens, which can be further prepared, and by setting and presenting an optimum electropolishing temperature and time.

In general, carburizing steel for automobile transmission is subjected to carburizing heat treatment at high temperature for high wear resistance and high strength such as fitting and torsional fatigue in durability and mass production.

Carburization is a heat treatment that allows carbon to diffuse into the surface layer of the steel by exposing the steel to a carbon atmosphere for 4 hours in a 900 ° C high temperature furnace, whereby hardness can rise above the Hv 780, which is a durable requirement. have.

After carburizing, quenching in oil or salt bath and tempering again at 180 ° C. for 2 hours.

Therefore, the microstructure of the carburized part is composed of plate-like martensite + residual austenite, and since the residual austenite has a great influence on the hardness and fitting of the shaft, and the torsional properties, it is important to accurately evaluate the amount. .

As one of the methods for evaluating the amount of retained austenite, the measurement method using EBSD (Electron Back Scattered Diffraction) measures the fraction of each phase in the whole area through mapping (mapping) to the area to be analyzed. Accurate measurement allows you to quantitatively determine the amount of phase you want in the area you want.

This EBSD measurement method is more accurate than any other equipment in that the resolution is several to several tens of mm.

In the measurement method using the EBSD, the surface portion of the specimen should be made strain or strain free, and for this purpose, the surface portion of the specimen is electroly polished to remove deformation of the surface portion.

Since electrolytic polishing can obtain excellent surface quality, not only the characteristics of the raw material state can be observed as it is, but the desired surface properties of the material can be grasped by obtaining a surface with less deformation.

1 is a cross-sectional view showing the residual stress after cutting the carburized steel specimen. For accurate EBSD measurement, the surface residual stress must be removed by electropolishing on the surface of the specimen.

The surface part of the carburized steel for transmission is usually about 0.8 wt%, and is very sensitive to corrosion by acid and the like, so that it is easily corroded even with a solution such as general nital.

Similarly, when electropolishing in carburized steel is highly sensitive to the electrolyte in the carburized portion, it is very difficult to determine the polishing conditions.

FIG. 2 is a photograph of the surface of the specimen subjected to electropolishing under the conventional electrolytic solution conditions most commonly used in steel materials, and Table 1 shows the amount of retained austenite (%) due to electrolytic solution and polishing conditions and EBS as a conventional measurement example. Measurement error is shown.

As shown in FIG. 2, the electropolished surface was very dirty and nonuniform, and the result could produce a very large error for determining the percentage by measuring EBSD.

Therefore, the present invention was invented to solve the above problems, and was prepared by adding methanol, propanol and acetic acid having excellent polishing properties as an electrolytic solution for electropolishing the surface portion of the carburized steel specimens. It is an object of the present invention to provide a method for electropolishing carburized steel specimens which can obtain a cleaner and superior surface quality compared to the conventional method.

In order to achieve the above object, the present invention, in the electrolytic polishing method of the carburized steel specimen to take the carburized steel specimen for EBSD measurement and to put it in the electrolytic solution and electropolishing the surface of the specimen, the surface portion of the carburized steel specimen An electrolytic solution for electropolishing was used as an electrolytic solution comprising vol% of perchloric acid 40%, methanol 5%, butoxyethanol 10%, propanol 10%, acetic acid 15% and distilled water 20%. To provide an electropolishing method of a carburized steel specimen.

Preferably, the electrolytic cell filled with the electrolytic solution is installed in a cooling tank, and then the electrolyte of the electrolytic cell is cooled by using a refrigerant circulating between the cooling tank and the cooler by a pump to maintain the temperature of the electrolyte.

Also preferably, the electrolytic polishing is performed for 25 seconds while maintaining the temperature of the electrolyte at -30 ° C.

The electropolishing method of the present invention is to improve the electropolishing quality required for the EBSD measurement, and it is possible to obtain a clean and strain-free surface quality which was impossible in the case of the conventional electrolytic solution in the carburized steel for the transmission. .

In addition, the electropolishing conditions of the present invention can accurately assess the amount of residual austenite at high and low magnifications, and can provide quantitative evaluation criteria for misleading sensitive issues and drawing regulations (usually measured up to 10,000 times). Is possible).

The electropolishing method of the present invention can be applied to all transmission parts subjected to carburization as well as shafts, and thus the scope of application is very wide, and can be usefully applied to EBSD measurement of carburized steel materials and parts.

In addition, the present invention has great significance in that it presents more accurate information from conventional inaccurate information in consideration of the significant effect of the amount of retained austenite on the physical properties of the transmission. Accurate predictions can be made and contribute effectively to quality improvement.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The present invention relates to an electropolishing method for a carburized steel specimen for electrolytic back scattered diffraction (EBSD) analysis, in order to improve non-uniform surface quality of the carburized steel specimen under conventional conditions during EBSD measurement. Electrolytic polishing conditions for the surface portion of the carburized steel (eg, carburized steel for transmission) specimens such as temperature are improved.

In order to measure EBSD, the surface of the specimen must be removed in the absence of residual stress, which is solved by electrolytic polishing.

Electropolishing cleans the surface of the specimen and reveals the physical properties of the raw material, making the image of the pattern distinct in EBSD.

However, because the carbon content of the carburized part is very high (more than 0.8 wt%), the specimens are very easily corroded and the electropolishing conditions are very demanding.

Thus, the present invention proposes a new electropolishing condition as shown in Table 2 below, and in this new electropolishing condition, it is possible to obtain a very clean and easy to measure surface quality when measuring EBSD.

First, the electrolyte solution of the present invention is composed of methanol, propanol and acetic acid having excellent polishing properties in order to increase the polishing effect, and in the preferred embodiment, the composition of the electrolyte solution is vol% 40% perchloric acid, methanol 5%, Butoxyethanol 10%, propanol 10%, acetic acid 15%, may be composed of distilled water 20%.

At the time of electropolishing, the electrolytic solution is kept at -30 ° C and the electropolishing time is performed at 25 seconds.

FIG. 3 is a flowchart showing the electropolishing process of the carburized steel specimen according to the present invention, and the specimen 2 is cut and taken from the carburized steel material or the carburized steel component 1 to be measured.

At this time, preferably, the specimen (2) is taken by cutting an end portion from a bar or a rectangular carburized steel material or a component (shaft) 1, and the cut surface of the once-collected specimen is sandpaper (# 2000). Grinding).

Thereafter, the electrolytic solution 4 is prepared in the electrolytic cell 3, the electrolytic cell 3 filled with the electrolytic solution 4 is placed in the cooling bath 5 filled with the refrigerant 6, and then the refrigerant in the cooling bath 5 is installed. Maintain and adjust the temperature to the set temperature.

In order to maintain the coolant temperature, the coolant 6 in the cooling bath 5 is circulated by the pump 8 between the cooler 7, cooled in the cooler 7, and then supplied into the cooling bath 5. The electrolytic cell 3 and the electrolyte solution 4 filled therein by the refrigerant 6 are cooled and maintained at a set temperature.

Subsequently, the specimen 1 is immersed in the electrolytic solution 4 in the electrolytic cell 3, and then electrolytic polishing is started by applying a voltage, and electropolishing is performed for a predetermined time.

The electropolishing finished specimen 2 is immersed and washed in a washing solution 9 such as ethanol, and the electropolishing and washed specimen 2 is used as a specimen for EBSD measurement.

In the electropolishing process as described above, an electrolyte solution composed of 40% perchloric acid, 5% methanol, 10% butoxyethanol, 10% propanol, 15% acetic acid, and 20% distilled water is used as a vol%, and the electrolyte temperature is a cooling system. It is maintained at -30 ° C by the refrigerant 6 circulated by (10), and electrolytic polishing is performed for 25 seconds in the cooling state of the electrolyte.

In the cooling system 10, 90% of methanol and 10% of ethanol are mixed with vol% as the refrigerant 6 which circulates between the cooling tank 5 and the cooler 7 and maintains the electrolyte in a cooling state.

4 is an electron microscopy image of the surface portion obtained by electropolishing the specimen taken from the cross section of the pinion shaft carburizing portion. It was confirmed that the surface portion (b) of the test piece electrolytically polished showed a cleaner surface state.

Meanwhile, FIG. 5 is a view showing a mapping image obtained by EBSD measurement after electropolishing using the electrolytic solution of the present invention, and shows a microstructure observed at a magnification of 2000 times on a specimen of a pinion shaft carburizing section.

(a) is an electron microscopy image obtained after electropolishing the specimen surface portion according to the electropolishing method of the present invention, and very clean surface quality could be obtained.

As a result of measuring EBSD under these surface polishing conditions, a clear and distinct image was obtained as shown in (c). Based on these results, the measurement area was determined at a surface area of 25 μm, which is a point to be measured, and then a mapping image was obtained. The residual austenite fraction can be accurately calculated in the desired measurement range.

1 is a cross-sectional view showing the residual stress after cutting the carburized steel specimen,

Figure 2 is a photograph of the surface of the specimen subjected to electropolishing in the conventional electrolyte solution conditions most commonly used in steel,

3 is a flowchart showing an electropolishing process of the carburized steel specimen according to the present invention;

4 is an electron microscope image of the surface portion obtained by electropolishing the specimen taken from the cross section of the pinion shaft carburizing portion,

5 is a view showing a mapping image obtained by EBSD measurement after electropolishing using the electrolyte solution of the present invention.

2: Psalm 3: Electrolyzer

4: electrolyte solution 5: cooling tank

6: refrigerant 7 cooler

8: pump 10: cooling system

Claims

In the electrolytic polishing method of the carburized steel specimen in which the carburized steel specimen is taken for EBSD measurement, and then it is placed in an electrolyte solution and subjected to electropolishing.

As an electrolyte for electropolishing the surface of the carburized steel specimens, an electrolyte solution composed of 40% perchloric acid, 5% methanol, 10% butoxyethanol, 10% propanol, 15% acetic acid and 20% distilled water was used as vol%. Electrolytic polishing of carburized steel specimens for EBSD analysis, characterized in that.

The method according to claim 1,

Carburizing steel specimens for EBSD analysis characterized in that the electrolytic cell filled with the electrolytic solution is installed in the cooling tank, and then cooled by using a refrigerant circulating between the cooling tank and the cooler by a pump to maintain the temperature of the electrolyte solution Electrolytic polishing method.

The method according to claim 1 or 2,

Electrolytic polishing method of the carburized steel specimen for EBSD analysis, characterized in that the electrolytic polishing for 25 seconds by maintaining the temperature of the electrolyte at -30 ℃.