KR20120097161A - Etching solution for exposure of austenite grain size and method for exposure of austenite grain size using thereof - Google Patents

Abstract

PURPOSE: An etching solution for observation of austenite grains and a method for etching a specimen using the same are provided to prevent damage to grains due to initial rapid etching by implementing etching in two stages. CONSTITUTION: A method for etching a specimen for observation of austenite grains comprises the steps of: dipping a specimen in a first etching solution, which comprises picric acid-saturated aqueous solution of 57.5-61.9vol.%, copper chloride of 0.1-0.5vol.%, and wetting agent of 38-42vol.%, to remove foreign materials from the surface of the specimen, adding hydrochloric acid of 0.01-0.05vol.% to the first etching solution of 100wt.% to obtain a second etching solution, dipping the specimen in the second etching solution, proceeding an etching process until an etching film is covered on the entire surface of the specimen from the second etching solution, and washing to remove the etching film from the specimen.

Description

ETCHING SOLUTION FOR EXPOSURE OF AUSTENITE GRAIN SIZE AND METHOD FOR EXPOSURE OF AUSTENITE GRAIN SIZE USING THEREOF}

The present invention relates to a corrosion method for a steel material and a specimen corrosion method using the same, and more particularly, by using a corrosion solution containing picric acid and copper chloride as corrosion solutions for observing austenite grains. In addition, the present invention relates to a technology for establishing corrosion conditions and ensuring reproducibility.

In order to predict the properties of steel materials or to interpret the relationship between the structure and properties of steels, it is necessary to observe and analyze austenite grains.

At this time, the austenite grain is a structure before the final phase of the steel material is formed.

Therefore, if the austenite grains are observed in advance, the state of the final phase can be predicted.

In the present invention, in performing a corrosion method, first, by using a corrosion solution of a weak acid base, and secondly using a corrosion solution added with a strong acid, it is possible to more easily and accurately observe austenite grains. It is an object to provide a method of surface corrosion of steel materials.

In addition, the present invention provides a corrosion solution containing picric acid and copper chloride as a corrosion solution of the weak acid base, and further provides a corrosion solution further including hydrochloric acid, advantageously establishing corrosion conditions and ensuring reproducibility. Its purpose is to make it possible.

Corrosion solution for observing austenite grains according to an embodiment of the present invention is saturated aqueous solution of picric acid: 57.5 to 61.9% by volume, copper chloride: 0.1 to 0.5% by volume and surfactant (Wetting Agent): 38 It is characterized by consisting of ~ 42% by volume.

In addition, the corrosion solution for observing austenite grains according to another embodiment of the present invention may further include 0.01 to 0.05 parts by volume of hydrochloric acid based on 100 parts by volume of the corrosion solution.

In addition, the corrosion method of the specimen for observing austenite grains according to an embodiment of the present invention is saturated aqueous picric acid (Picric Acid): 57.5 ~ 61.9% by volume, Copper Chloride: 0.1 ~ 0.5% by volume and the surfactant ( Wetting Agent): a first corrosion step of removing a foreign substance present on the surface of the specimen by depositing the specimen to be observed austenite grains in the first corrosion solution consisting of 38 ~ 42% by volume, and the first corrosion solution 100 Depositing the specimen in a second corrosion solution to which 0.01 to 0.05 parts by volume of hydrochloric acid is further added to the volume part, and performing the corrosion coating formed on the surface of the specimen by the second corrosion solution on the entire surface of the specimen. It characterized in that it comprises a washing step of removing the corrosion coating formed on the specimen through two corrosion and washing step.

In the present invention, in order to prepare a specimen for observing austenite grains, after the initial corrosion of the specimen by using a weak acid-based corrosion solution containing primarily picric acid and copper chloride, a second additional corrosion acid solution is used. To perform the remaining corrosion. Therefore, it is possible to prevent grain damage due to rapid corrosion reaction at the initial stage of corrosion, and to control the overall corrosion reaction time and etching degree easily.

Therefore, when using the method for corroding the austenite grains and the corrosive solution for observing the austenite grains according to the present invention it is possible to more easily and accurately observe austenite grains.

1 is a specimen photograph showing the austenite grain observation results according to a comparative example of the present invention.
Figure 2 is a specimen photograph showing the austenite grain observation results according to another embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to the corrosion method of the austenitic grain observation corrosion solution and the austenitic grain observation specimen according to a preferred embodiment of the present invention.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

In the present invention, 'crystal grain observation' refers to observing grains having a microscopic size in a metal material, and may also be referred to as 'grain grain observation'.

By optimizing the addition amount of aqueous picric acid solution, copper chloride and surfactant, the present invention provides a corrosion solution that can be applied irrespective of carbon content and steel type and can exhibit austenite grains in a short time.

As an example, the corrosion solution for austenite grain observation according to the present invention is saturated aqueous solution of picric acid: 57.5 to 61.9% by volume, copper chloride: 0.1 to 0.5% by volume and surfactant (Wetting Agent): 38 It provides a first corrosion solution consisting of ~ 42% by volume, and a second corrosion solution containing 0.01 to 0.05 parts by volume of hydrochloric acid relative to 100 parts by volume of the first corrosion solution.

First, the reason for the restriction of the concentration and the amount of the aqueous solution applied to the first corrosion solution is as follows.

Picric acid aqueous solution in the present invention is an effective component for causing a total corrosion on the surface of the steel, the concentration of the aqueous solution of picric acid should be saturated.

If the concentration of the picric acid aqueous solution is unsaturated or the amount of the picric acid aqueous solution added is less than 57.5% by volume of the total volume of the corrosion solution, full corrosion does not occur. On the contrary, when the concentration of the picric acid aqueous solution is in the supersaturated state or the addition amount exceeds 61.9% by volume, corrosion of the entire surface is excessively performed, so that grains do not appear clearly.

Therefore, while the concentration of the picric acid aqueous solution is used in a saturated state, it is preferable to limit the addition amount to 57.5 ~ 61.9% by volume.

Next, copper chloride is the most important component of the present invention effective to manifest the grains of austenite. The copper component is colored in the austenite crystal grains to facilitate observation.

Therefore, when the addition amount of copper chloride is less than 0.1% by volume, the coloring effect is almost insignificant, and when the addition amount of copper chloride is more than 0.5% by volume, the coloring becomes too excessive, making it difficult to observe the boundary or distinct grains. There is.

Next, the surfactant serves to facilitate the observation of austenite grains while suppressing the phenomenon of over-corrosion of the steel surface by copper chloride.

As the surfactant, an aqueous dodecylbenzene sulfonic acid sodium salt (C ₁₂ H ₂₅ C ₆ H ₄ SO ₃ Na) having a concentration of 40 to 50% may be used.

Here, the concentration of 40 to 50% means that the dodecylbenzene sulfonic acid sodium salt (C ₁₂ H ₂₅ C ₆ H ₄ SO ₃ Na) solution is mixed with water at a ratio of 40 to 50% by weight.

At this time, when the concentration of the aqueous dodecylbenzene sulfonic acid sodium salt solution is less than 40%, the characteristics as a surfactant do not appear completely. On the contrary, when the concentration of the aqueous dodecylbenzene sulfonic acid sodium salt solution exceeds 50%, it may be difficult to control the degree of corrosion and thus it may not be easy to observe grains.

Therefore, the addition effect of the surfactant according to the present invention may be insufficient if it is less than 38% by volume. In contrast, when the amount of the surfactant added exceeds 42% by volume, it is difficult to control the corrosion.

After preparing the first corrosion solution using the aqueous solution of picric acid, copper chloride and sodium dodecylbenzene sulfonic acid described above, by using the second corrosion solution with secondary acid addition, the austenite grains can be observed more easily and accurately. Make it work.

In this case, hydrochloric acid may be used as the strong acid used in the second corrosion solution. The strong acid is preferably added in an amount of 0.01 to 0.05 parts by volume with respect to 100 parts by volume of the first solution. If the amount of strong acid added is less than 0.01 parts by volume, the effect on the use of the second corrosion solution cannot be obtained. On the contrary, when the addition amount of the strong acid exceeds 0.05 parts by volume, corrosion of the steel surface may be excessively performed, making it difficult to observe austenite grains.

As described above, the reason why the first corrosion solution based on the weak acid base is primarily used in the present invention is to efficiently control the initial corrosion reaction.

In the case of strong acids, the degree of corrosion is difficult to control. This is because the surface reaction occurs rapidly. In this case, not only the austenite grain boundary but also the grain boundary of the current structure of the material such as ferrite and ferrite may be strongly corroded, and thus it may be difficult to observe a desired part.

Therefore, in the present invention, in order to easily control the time and the degree of etching of the initial corrosion reaction, the first corrosion solution as described above is used.

And, by using the second corrosion solution secondarily, the austenite grains selectively corroded by the primary solution appear more clearly. At this time, the crystal grains may be observed even when only the second corrosion solution is used without using the first corrosion solution, but no clear result was obtained as shown in FIG. 2.

Hereinafter, the corrosion method of the specimen for observing austenite grains using the first and second corrosion solutions according to the present invention will be described.

The method for preparing a specimen for austenite grain observation according to the present invention includes a first corrosion step, a second corrosion step, and a washing step.

In the first corrosion step, the specimen to be observed for austenite grains is deposited in the first corrosion solution to initially corrode the surface of the specimen. In this process, foreign matter present on the surface of the specimen may be removed.

As described above, the first corrosion solution is composed of saturated aqueous picric acid: 57.5 to 61.9% by volume, copper chloride: 0.1 to 0.5% by volume and 40 to 50% of dodecylbenzene sulfonic acid sodium salt: 38 to 42% by volume. It is available.

As described above, the surface of the specimen is initially corroded with a weak acid-based corrosion solution to remove foreign substances, and a rapid corrosion reaction can be prevented to easily control the corrosion time and the degree of corrosion.

The sample is deposited for 20 to 30 seconds while the first corrosion solution is heated to 75 to 80 ° C.

In this case, when the temperature of the total deposition process using the first corrosion solution is less than 75 ° C., or when the deposition time is performed in less than 20 seconds, corrosion reaction or surface coloring may not be completely performed, and thus it may not be easy to observe austenite grains. .

On the contrary, when the temperature exceeds 80 ° C. or the deposition time exceeds 30 seconds, the corrosion reaction may be excessively performed, making it difficult to observe austenite grains.

In this case, since the use of the first corrosion solution is to finely control the surface state of the initial specimen, it is preferable to perform the deposition process one to three times while periodically monitoring the surface of the specimen using a microscope. Do.

Therefore, if the total deposition process is performed less than two times, the austenite grains may not be clearly seen. If the total deposition process is more than four times, the corrosion reaction is excessively performed, resulting in damage to the austenite grains and observation. It can be difficult.

Next, in order to more clearly express the state of austenite grains, the present invention prepares a second corrosion solution in which 0.01 to 0.05 parts by volume of hydrochloric acid is further added to 100 parts of the first corrosion solution. Secondary corrosion of the specimens with initial primary corrosion is used.

At this time, the second corrosion solution is also maintained at 75 ~ 80 ℃, the time is performed until the foreign matter film is uniformly formed on the surface of the specimen.

When the temperature of the second corrosion solution is less than 75 ° C., it is difficult to form a uniform foreign substance film. When the temperature of the second corrosion solution exceeds 80 ° C., overcorrosion occurs, making it difficult to observe grains.

Here, the 'time when the foreign material film is uniformly formed' means the time when the metallic luster of the specimen surface disappears and a black corrosion coating is formed on the entire surface of the surface. It is difficult to determine the specified time because it varies from sample to sample.

However, as a result of measuring the average time of the various specimens, the deposition retention time using the second corrosion solution was appropriately 30 seconds to 1 minute, but is not limited thereto.

Next, since the secondary corrosion is completed as described above, it is difficult to observe the austenite grains due to the corrosion coating formed on the surface, by performing a separate cleaning process, to remove the corrosion coating.

At this time, the washing is preferably carried out in a manner that the sample is first washed in running water and then washed twice with alcohol and then dried.

Here, the reason for performing the first and second cleaning is that the corrosion coating may remain as a stain when the corrosion coating is not completely removed, and thus it may not be easy to observe austenite grains.

As described above, by using the method of corroding the specimen according to the present invention, it is possible to exhibit more sharp austenite grains.

Therefore, looking at the specific embodiment as follows.

First, the specimens were immersed three times each for 30 seconds in a first corrosive solution having a concentration and an addition amount of an aqueous solution of picric acid, copper chloride, and sodium dodecylbenzene sulfonic acid solution as shown in Table 1 below. The results are shown in Table 1 below.

[Table 1]

As shown in Table 1, the first corrosive solution of Examples 1 and 2 according to the scope of the present invention was found to be suitable to exhibit a clear austenite grains, Comparative Examples 1 to 5 outside the scope of the present invention It can be seen that the corrosion solution is not suitable for grain appearance.

Next, the second corrosion solution was prepared by adding hydrochloric acid to Examples 1 and 2, but was performed under the conditions of Table 2 below.

In each case, austenite grains were observed, and according to the degree of observation,? Was excellent,? Was good,? Was insufficient, and? Was poor, and the results were shown.

[Table 2]

As can be seen from Table 2, even when using the first corrosion solution that satisfies the scope of the present invention, a sharper austenite grains could not be exhibited when the second corrosion solution was incorrectly used.

1 is a specimen photograph showing the austenite grain observation results according to a comparative example of the present invention.

In the specimen of FIG. 1, the heat treated API X50 steel was used, and according to Comparative Example 4, 57.5 ml of saturated saturated picric acid, Copper Chloride 510 mg (0.51 ml), and 51% dodecylbenzene were used. 41.99 ml of aqueous sulfonic acid sodium salt solution was mixed to prepare a first corrosion solution.

Next, the step of immersing for 30 seconds while heating the first corrosion solution to 75 ~ 80 ℃ was performed three times.

Subsequently, the final corrosion was completed by using the second corrosion solution in which 0.01 parts by weight of hydrochloric acid was added to 100 parts by weight of the first corrosion solution, and after washing, austenite grains were observed on the cross section of the specimen.

As a result, as shown, the corrosion state is also insufficient, the characteristic of overdiscoloration due to excessive addition of copper chloride appeared, it can be seen that the surface is difficult to observe.

Figure 2 is a specimen photograph showing the austenite grain observation results according to another embodiment of the present invention.

As the specimen of FIG. 2, API X50 steel was heat-treated, and 60.0 ml of saturated saturated picric acid, 100 mg (0.1 ml) of copper chloride and 39.9 ml of sodium dodecylbenzene sulfonic acid solution were mixed. A first corrosion solution was prepared.

Next, the step of immersing for 30 seconds while heating the first corrosion solution to 75 ~ 80 ℃ was performed three times.

Subsequently, the final corrosion was completed by using the second corrosion solution in which 0.01 parts by weight of hydrochloric acid was added to 100 parts by weight of the first corrosion solution, and after washing, austenite grains were observed on the cross section of the specimen.

As a result, as shown, it was possible to obtain a clear and clear grain image, a clear austenite grain observation results.

As described above, in performing the corrosion method, the present invention makes it easier and more accurate to observe austenite grains by first using a corrosion solution of a weak acid base and then using a corrosion solution to which a strong acid is added second. Can be done.

In addition, the present invention provides a corrosion solution containing picric acid and copper chloride as a corrosion solution of the weak acid base, and further provides a corrosion solution further including hydrochloric acid, advantageously establishing corrosion conditions and ensuring reproducibility. can do.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications may belong to the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention will be determined by the claims described below.

Claims (8)

Saturated aqueous solution of picric acid: 57.5 to 61.9% by volume, copper chloride: 0.1 to 0.5% by volume and surfactant (Wetting agent): 38 to 42% by volume for austenite grain observation Corrosion solution.
The method of claim 1,
The surfactant is
Corrosion solution for austenite grains observation, characterized in that the aqueous solution of dodecylbenzene sulfonic acid sodium salt (C ₁₂ H ₂₅ C ₆ H ₄ SO ₃ Na) having a concentration of 40 to 50%.
The method of claim 1,
The corrosion solution is
Corrosion solution for austenite grains observation characterized in that it further comprises 0.01 to 0.05 parts by volume hydrochloric acid with respect to 100 parts by volume of the corrosion solution.
Observation of austenite grains in a first corrosion solution consisting of saturated aqueous solution of Picric Acid: 57.5 to 61.9% by volume, Copper Chloride: 0.1 to 0.5% by volume, and Wetting Agent: 38 to 42% by volume. Depositing a specimen to be subjected to a first corrosion step of removing foreign matter present on the surface of the specimen;
The specimen is immersed in a second corrosion solution, in which 0.01 to 0.05 volume parts of hydrochloric acid is further added to 100 parts of the first corrosion solution, and a corrosion coating formed on the surface of the specimen by the second corrosion solution is to be formed on the entire surface of the specimen. Performing a second corrosion step until; And
Corrosion method of the specimen for observing austenite grains comprising a; washing step of removing the corrosion coating formed on the specimen by washing.
The method of claim 4, wherein
The first corrosion step
Corrosion method of the specimen for austenite grain observation, characterized in that carried out for 20 to 30 seconds at a temperature of 75 ~ 80 ℃.
The method of claim 4, wherein
The first corrosion step
Corrosion method of the specimen for observing austenite grains, characterized in that it is carried out 2 to 4 times.
The method of claim 4, wherein
The second corrosion step
Corrosion method of the specimen for austenite grain observation, characterized in that carried out at 75 ~ 80 ℃.
The method of claim 4, wherein
The washing step
The first method of washing the specimen using running water, and then the second method is washed with alcohol using austenite grains corrosion method of the specimen for observation.

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