KR20200039926A - Etchant for microstructure analysis for heat treated medium carbon steel by high frequency currents and etching method using the same - Google Patents

Abstract

The present invention relates to an etching solution which can be suitably used when observing a microstructure of high-frequency heat-treated carbon steel with a large difference between an internal structure and a surface structure, suppress unevenness of etching on a surface portion and the generation of adsorbents generated in an etching process, and thus enables the acquisition of etching structure to make analysis easy. The etching solution according to the present invention is composed of: 1.8-2.0 wt% of picric acid, 2.4-2.6 wt% of sodium dodecylbenzenesulfonate, 1-2 wt% of hydrochloric acid, 0.01-0.02 wt% of cupric chloride, and 0.004-0.01 wt% of ferric chloride, and a balance solvent.

Description

Etching solution for microstructure analysis of high-frequency heat-treated medium carbon steel, and etching method using the same {ETCHANT FOR MICROSTRUCTURE ANALYSIS FOR HEAT TREATED MEDIUM CARBON STEEL BY HIGH FREQUENCY CURRENTS AND ETCHING METHOD USING THE SAME}

The present invention relates to an etching solution used for observing the microstructure of high-frequency heat-treated carbon steel and an etching method using the etching solution.

In order to analyze the crystal grain size, which is one criterion of a method for evaluating the physical properties / quality of a metal, an etching process is required to etch the surface of the mirror-polished metal to reveal crystal grain boundaries before analysis under a microscope.

As a method of etching the surface of medium carbon steel, conventionally, an etching solution consisting of 100 to 120 ml of water, 4 to 5 g of picric acid, 4 to 5 g of surfactant, and 0.4 to 1.0 ml of hydrochloric acid (HCl) is heated and maintained at 60 to 90 ° C. A method is known that includes a step, immersing the test piece in the solution and maintaining it for 40 to 60 seconds, and taking the test piece out of the solution, washing and drying it.

By the way, in the case of medium-high-frequency heat-treated medium carbon steel (C: 0.3 to 0.5% by weight), the internal structure is composed of a mixed structure of ferrite and pearlite, and the surface structure is converted to martensite by heat treatment. When the above-described etching method is applied, the internal structure is over-etched and the surface structure has a problem that the boundary of the crystal grains is faintly etched due to a difference in corrosion rate between the internal and surface tissues. Black adsorbate is formed in the tissue, which causes difficulty in analyzing the grains.

Republic of Korea Patent Publication No. 1995-0019701

One object of the present invention, in the measurement of the crystal grain size of the surface portion of the high-frequency heat-treated medium carbon steel (C: 0.3 ~ 0.5% by weight), to solve the problem of the non-uniform etching of the high-frequency heat-treated portion or adsorption of oxides, microstructure It is to provide an etching solution that can be clearly manifested.

Another object of the present invention is to provide an etching method that allows the microstructure to be clearly exhibited using the etching solution.

The etching solution of the present invention for achieving the above object, picric acid: 1.8 ~ 2.0 wt%, sodium dodecylbenzenesulfonate: 2.4 ~ 2.6 wt%, hydrochloric acid: 1 ~ 2 wt%, cupric chloride: 0.01 ~ 0.02% by weight, ferric chloride: 0.004 to 0.01% by weight, and characterized in that it contains a residual solvent.

The etching method of the present invention for achieving the other object, in the solvent, picric acid: 1.8 to 2.0% by weight, dodecylbenzenesulfonate: 2.4 to 2.6% by weight, hydrochloric acid: 1 to 2% by weight, cupric chloride : 0.01 to 0.02% by weight, and ferric chloride: adding 0.004 to 0.01% by weight, mixing the added materials by stirring at 60 to 65 ° C., and mirror-polished test pieces in the mixed solvent. It characterized in that it comprises a step of immersing for a predetermined time, and washing and drying the immersed test piece.

According to the etching solution and the etching method using the etching solution according to the present invention, it is possible to uniformly develop the microstructure of the high-frequency heat-treated medium carbon steel, and minimize the generation of black adsorbent generated on the surface of the high-frequency heat-treated product during the etching process. , Facilitates the analysis of microstructures.

1 is a microstructure of the high-frequency heat-treated medium carbon steel etched using the etching method according to Example 1 of the present invention is observed with an optical microscope.
Figure 2 is a microstructure of the high-frequency heat-treated medium carbon steel etched using the etching method according to the second embodiment of the present invention observed with an optical microscope.
3 is a microstructure of the high-frequency heat-treated medium carbon steel etched using the etching method according to the comparative example is observed with an optical microscope.

Hereinafter, an etching solution according to exemplary embodiments and an etching method using the same will be described in more detail. However, the following embodiments are presented as examples, whereby the invention is not limited and the invention is defined by the scope of the claims below.

Conventionally, in the case of an etching solution and an etching method used to express crystal grains on the surface portion of the high-frequency heat-treated medium carbon steel, it is difficult to clearly exhibit crystal grains on the high-frequency heat-treated surface portion or black adsorbents are generated to analyze the microstructure. There was a problem that this was not easy, and the present inventors made extensive studies to solve this problem, and as a result, increased the concentration of hydrochloric acid and added copper chloride and ferric chloride compared to the conventional etching solution, thereby clear crystal grains appeared. It has been found that this is possible and that the generation of black adsorbate can also be suppressed, leading to the present invention.

The etching solution according to an embodiment of the present invention, picric acid: 1.8 ~ 2.0 wt%, sodium dodecylbenzenesulfonate: 2.4 ~ 2.6 wt%, hydrochloric acid: 1 ~ 2 wt%, cupric chloride: 0.01 ~ 0.02 wt %, Ferric chloride: 0.004 to 0.01 wt% and the balance solvent.

The picric acid is a compound called 2,4,6-trinitrophenol among trinitrophenols having several isomers, and the chemical formula is C ₆ H ₃ N ₃ O ₇ , and the chemical formula is C ₆ H ₂ (OH) (NO ₂ ) ₃ , the aqueous solution has a strong acidity, is an unstable and explosive combustible material. In the present invention, picric acid serves to finely corrode grain boundaries, and if the content of picric acid is less than 1.8% by weight, sufficient etching is not performed, and if it exceeds 2.0% by weight, stability of the etching solution is inhibited, so within 1.8 to 2.0% by weight. It is preferably included.

The sodium dodecylbenzenesulfonate is a kind of anionic surfactant, which serves to dissolve an aromatic compound in a polar solvent, and if it is not added within a range of 2.4 to 2.6% by weight, it is possible to obtain etching characteristics required by the present invention. Since it is difficult to be absent, it is preferable to maintain the above range.

When the content of the hydrochloric acid is less than 1% by weight, it is difficult to etch the high-frequency heat-treated surface portion like a conventional etching solution, and when it exceeds 2% by weight, the acidity is excessively high, making it difficult to control the etching conditions, so 1 to 2 It is preferred to be included in weight percent.

The cupric chloride and ferric chloride serve as weak oxidizing agents in the etching solution, respectively, as shown in [Formula 1] and [Formula 2] below, a reaction site located on the surface of the high-frequency heat-treated medium carbon steel. It serves to induce etching by an electron transfer mechanism between Cu ²⁺ ions and Fe ³⁺ ions contained in the etching solution. When the cupric chloride and ferric chloride are not added within the above range, it is difficult to obtain the effect according to the present invention, so it is preferable to add the above range.

[Equation 1]

Fe + CuCl ₂ → FeCl ₂ + Cu

[Equation 2]

Fe + 2FeCl ₃ → 3FeCl ₂

In addition, in the etching solution of the present invention, the solvent is not particularly limited as long as it can dissolve picric acid, sodium dodecylbenzenesulfonate, cupric chloride, and ferric chloride, but one selected from ethanol, methanol, and distilled water It is preferable to use the above.

In addition, the etching solution of the present invention can be suitably used for medium-carbon steel, which is particularly high-frequency heat-treated, but can also be used for the appearance of microstructures heat-treated by other methods, and is not particularly limited to the heat-treatment method.

In addition, the etching method according to an embodiment of the present invention, in the solvent, picric acid: 1.8 to 2.0% by weight, dodecylbenzenesulfonate: 2.4 to 2.6% by weight, hydrochloric acid: 1 to 2% by weight, cupric chloride : 0.01 to 0.02% by weight, and ferric chloride: adding 0.004 to 0.01% by weight, mixing the added materials by stirring at 60 to 65 ° C., and mirror-polished test pieces in the mixed solvent. It provides an etching method comprising the step of immersing a predetermined time, and cleaning and drying the immersed test piece.

When mixing the added material, when the temperature is less than 60 ° C, the mixing efficiency decreases, and when it exceeds 65 ° C, the concentration of the etchant is rapidly increased, so it is preferable to maintain 60 to 65 ° C because it is difficult to control the etching process.

Specimens requiring tissue observation must first be mirror polished. The mirror polishing can be performed through a coarse polishing step and a fine polishing step, and in the final step, it is preferable to use an abrasive containing 1 to 2 μm alumina powder.

When the immersion time of the immersion step of the test piece is less than 20 seconds, the microstructure may not be sufficiently exhibited, and if it is more than 30 seconds, the microstructure may be overetched, so it is preferably performed for 20 to 30 seconds.

The washing step of the test piece may be preferably performed with distilled water and / or ethanol.

In addition, the carbon content of the medium carbon steel may be preferably 0.3 to 0.5% by weight.

In addition, the immersion step of the test piece includes a first immersion step, a cleaning step of the test piece that has performed the first immersion step, and a second immersion step of immersing the cleaned test piece in the etching solution again. As described above, if the first immersion step is performed after a short period of cleaning and then the second immersion step is performed, the generation of black adsorbent generated on the high-frequency heat-treated surface portion can be further suppressed and the etching result Reproducibility can also be increased, which is preferable. At this time, the first immersion step and the second immersion step may be performed for 10 to 20 seconds, respectively, which is a relatively short time compared to a method of performing only one immersion step.

[Example]

Preparation of etching solution

To 150 ml of distilled water, 3 g of picric acid, 4 g of sodium dodecylbenzenesulfonate, 2 ml of hydrochloric acid, 0.02 g of cupric chloride, and 0.01 g of ferric chloride were added, heated to a temperature of 60 to 65 ° C, and then at a level of 650 to 700 rpm. Through the stirring method, an etching solution according to an embodiment of the present invention was prepared.

In addition, as a comparative example for comparison with the etching solution according to the embodiment of the present invention, while mixing 4.5 g of picric acid, 4.5 g of dodecylbenzenesulfonate, and 0.7 ml of hydrochloric acid in 110 ml of distilled water, while maintaining the heating at 70 to 80 ° C Existing etching solutions were prepared using the stirring method.

Etching method

First, the high-frequency heat-treated medium carbon steel test piece was cut to a size of 10 × 10 cm and subjected to light grinding.

The mirror-polished test piece was immersed in an etching solution prepared according to an embodiment of the present invention for 25 seconds, and then washed with distilled water (Example 1).

In addition, after the mirror-polished test piece is immersed in an etching solution prepared according to an embodiment of the present invention for 15 seconds (first immersion step), washed with distilled water, and then again immersed in the etching solution for 15 seconds (second immersion) Step), and washed with distilled water (Example 2).

Further, the mirror-polished test piece was immersed in an etching solution prepared according to a comparative example for 40 seconds and then washed with distilled water (comparative example).

Analysis of microstructure

1 is a microstructure of the high-frequency heat-treated medium carbon steel etched using the etching method according to the first embodiment of the present invention is taken with an optical microscope, Figure 2 is using the etching method according to the second embodiment of the present invention The microstructure of the etched high-frequency heat-treated medium carbon steel was photographed with an optical microscope, and FIG. 3 is an optical microscope of the microstructure of the high-frequency heat-treated medium carbon steel etched using the etching method according to the comparative example.

1 and 2, in the case of the specimen etched according to the embodiment of the present invention, there is almost no generation of black adsorbent generated in the high-frequency heat-treated medium carbon steel, and the crystal grains on the surface and inside are clearly You can see that it is on the move. In particular, in the case of Example 2, it can be said that it is more preferable because the crystal grains can be clearly exhibited without generating black adsorbents for various steels compared to Example 1.

On the other hand, when a different etching method was applied to the comparative example, it was not only suitable for the analysis of the microstructure, because it was not only colored, but crystal grains on the surface were not clearly observed.

Claims (8)

Picric acid: 1.8-2.0 wt%,
Sodium dodecylbenzenesulfonate: 2.4 to 2.6 wt%,
Hydrochloric acid: 1 to 2% by weight,
Cupric chloride: 0.01 to 0.02% by weight,
Ferric chloride: 0.004 to 0.01 wt%
And a residual solvent, an etching solution for microstructure analysis of the heat-treated medium carbon steel. According to claim 1,
The solvent is at least one selected from ethanol, methanol and distilled water, an etching solution for microstructure analysis of heat-treated medium carbon steel. According to claim 1,
The heat treatment is a high-frequency heat treatment, an etching solution for microstructure analysis of the heat treated medium carbon steel. In the solvent, picric acid: 1.8 to 2.0 wt%, sodium dodecylbenzenesulfonate: 2.4 to 2.6 wt%, hydrochloric acid: 1 to 2 wt%, cupric chloride: 0.01 to 0.02 wt%, and ferric chloride: 0.004 Adding ~ 0.01% by weight,
And mixing the added substances by stirring at 60 ~ 65 ℃,
Immersing the mirror-polished test piece in the mixed solvent for a predetermined time,
Cleaning and drying the immersed test piece,
Etching method for microstructure analysis of heat treated medium carbon steel. According to claim 4,
The immersion time of the immersion step of the test piece is performed for 20 to 30 seconds, the etching method for microstructure analysis of the heat-treated medium carbon steel. According to claim 4,
Cleaning of the test piece is performed with distilled water or ethanol, an etching method for microstructure analysis of heat-treated medium carbon steel. According to claim 4,
The carbon content of the medium carbon steel is 0.3 ~ 0.5% by weight, an etching method for microstructure analysis of the heat treated medium carbon steel. According to claim 4,
The immersion of the test piece is performed including a first immersion step, a cleaning step of the test piece that has performed the first immersion step, and a second immersion step of immersing the cleaned test piece in the etching solution again,
The first immersion step and the second immersion step are each performed for 10 to 20 seconds, an etching method for microstructure analysis of the heat treated medium carbon steel.

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