1. A metallographic corrosive agent for austenitic Fe-Mn-Al-C series low-density high-strength steel is characterized by comprising picric acid, ferric chloride, concentrated hydrochloric acid and absolute ethyl alcohol, and the mixture ratio of the picric acid to the ferric chloride to the concentrated hydrochloric acid is as follows: 1-3g of picric acid, 2-6g of ferric trichloride, 4-6ml of concentrated hydrochloric acid and 100ml of absolute ethyl alcohol.

2. The metallographic etchant according to claim 2, wherein the concentration of the concentrated hydrochloric acid is 36% -38%.

3. A method of preparing a metallographic etchant according to claim 1 or 2, comprising the steps of:

1) adding picric acid into part of anhydrous ethanol, and dissolving to obtain a mixed solution a;

2) adding ferric chloride into the mixed solution a, and stirring to completely dissolve the ferric chloride to form mixed solution b;

3) adding the residual absolute ethyl alcohol into the mixed solution b to prepare a mixed solution c;

4) and pouring concentrated hydrochloric acid into the mixed solution c, uniformly stirring, and standing for 3-5 minutes to obtain the target corrosive.

4. The method for preparing a metallographic etchant according to claim 3, wherein in step 1, picric acid is added after absolute ethyl alcohol is heated to 40-50 ℃.

5. The corrosive agent for metallographic phases according to claim 3, wherein in said step 1, the volume of absolute ethyl alcohol for dissolving picric acid is 1/3-1/2 of the total volume of absolute ethyl alcohol.

6. Use of the metallographic etchant according to claim 1 or 2 for metallographic etching of austenitic Fe-Mn-Al-C low-density high-strength steel, wherein the metallographic etchant is dipped and cleaned and dried after the polished surface of the sample to be tested is wiped until the color of the polished surface becomes grey.

7. The use according to claim 6, characterized in that the test specimen to be tested is subjected to rough grinding, fine grinding, polishing, cleaning and drying before etching to obtain a bright and scratch-free test specimen surface.

8. The application of claim 6, wherein the metallographic corrosive agent is heated to 30-40 ℃ and then dipped and wiped on the sample to be detected, and the time for wiping the sample to be detected by the metallographic corrosive agent is 5-10 s.

9. The use according to claim 6, wherein the cleaning is performed by flushing with running water for 4-5 seconds.

10. The use of claim 6, wherein the drying is performed by blowing the sample test surface in one direction with a blower until no water is present.

Background

The austenite Fe-Mn-Al-C series low-density high-strength steel comprises the following internal elements in percentage by mass: 15-30% of Mn; 2-12% of Al; c is greater than 0.5%; the balance of Fe; the alloy is developed by adding Al and C elements on the basis of high manganese steel, and compared with other light materials, the alloy has considerable combination of mechanical properties and low density, so that the alloy has great application prospects in light weight of automobiles. The steel can be used only after high-temperature solid solution and low-temperature aging treatment, the main structure of the steel is austenite, high-temperature alpha ferrite and k carbide precipitates, and the high-temperature alpha ferrite, k carbide and other structures formed by the high-temperature solid solution and low-temperature aging treatment process have great influence on the performance of the steel.

The metallographic corrosion method of the steel is only reported, the metallographic analysis is used as an important analysis means for the research and development of new materials, and the research on the relationship between the internal structure of the material and the process performance is also one of the main contents of the metallographic analysis, so that the metallographic corrosion method of the steel is required to be searched.

At present, no report is found on the metallographic corrosion method of austenitic Fe-Mn-Al-C series low-density high-strength steel. The prior art only discloses a method for carrying out metallographic corrosion on high manganese steel, and the formula is as follows: (a) 3% -5% of nitric acid absolute ethyl alcohol; (b) 4% -6% of hydrochloric acid absolute ethyl alcohol; the corrosion method comprises the steps of etching for 5-20s in the step (a), taking out a sample, washing and drying the sample by using clear water, and etching for 5-10s in the step (b).

Therefore, it is very important to develop a metallographic etching method which can clearly and completely display the metallographic structure of austenitic Fe-Mn-Al-C low-density high-strength steel with simple operation.

Disclosure of Invention

The first purpose of the invention is to provide a metallographic corrosive agent for austenitic Fe-Mn-Al-C series low-density high-strength steel, the second purpose of the invention is to provide a preparation method of the metallographic corrosive agent, and the third purpose of the invention is to provide application of the metallographic corrosive agent.

The first purpose of the invention is realized by the following steps of: 1-3g of picric acid, 2-6g of ferric trichloride, 4-6ml of concentrated hydrochloric acid and 80-100ml of absolute ethyl alcohol.

The second purpose of the invention is realized by the method for preparing the metallographic corrosive agent, which comprises the following steps:

1) adding picric acid into part of anhydrous ethanol, and dissolving to obtain a mixed solution a;

2) adding ferric chloride into the mixed solution a, and stirring to completely dissolve the ferric chloride to form mixed solution b;

3) adding the residual absolute ethyl alcohol into the mixed solution b to prepare a mixed solution c;

4) and (5) when the mixed solution c is cooled to room temperature, pouring concentrated hydrochloric acid, uniformly stirring, and standing for 3-5 minutes to obtain the target corrosive.

The third purpose of the invention is realized by applying the metallographic corrosive to the metallographic corrosion of austenitic Fe-Mn-Al-C series low-density high-strength steel, and the specific method is that the metallographic corrosive is dipped and wiped on the polished surface of the sample to be tested for 5-10s until the color of the polished surface is grayed, and then the polished surface is cleaned and dried.

The principle of the invention is as follows:

the austenite Fe-Mn-Al-C series low-density high-strength steel mainly comprises an austenite structure, a high-temperature alpha ferrite structure and a k carbonized educt, wherein the austenite structure can be effectively corroded by Cl ions in hydrochloric acid, the high-temperature alpha ferrite and the k carbonized educt can be displayed by picric acid, the high-oxidizing nitric acid can easily cover the high-temperature alpha ferrite and the k carbonized educt structures in the corrosion process, ferric trichloride with slightly weak oxidizing property is selected to replace the nitric acid, and meanwhile, absolute ethyl alcohol is used as a corrosion inhibitor to ensure the uniformity of corrosion. Therefore, picric acid, hydrochloric acid, ferric trichloride and absolute ethyl alcohol are selected as main components of the corrosive. Moreover, the proportion of each component can ensure that the structure is clearly displayed and simultaneously can avoid the dissolution of ferrite or carbide caused by corrosion to the maximum extent: under the condition that the hydrochloric acid proportion in the corrosive is more (more than 10ml/100ml of absolute ethyl alcohol), the austenite grain boundary is excessively corroded, and the detail characteristics of carbide precipitated on the grain boundary cannot be displayed and observed; when the hydrochloric acid amount is too small, the austenite grain boundary display is incomplete, and the related analysis work such as grain size rating is inconvenient; the saturated solution of ferric trichloride absolute ethyl alcohol (about 60g/100ml absolute ethyl alcohol) can have better etching effect on austenite crystal boundaries, but carbon precipitate particles on the crystal boundaries are dissolved due to strong corrosivity; in addition, the hydrochloric acid absolute ethyl alcohol solution has a certain display effect on austenite crystal boundaries, so only a small amount (2 g-6 g/100ml absolute ethyl alcohol) of ferric trichloride is added into the corrosive agent.

The invention has the beneficial effects that:

1) the metallographic corrosive provided by the invention can clearly and completely display the structures of austenite, high-temperature alpha ferrite and k-carbonized educt in the austenitic Fe-Mn-Al-C low-density high-strength steel, the color and the morphology of the structures do not influence the observation and the rating of the structures, and a technical support is provided for the analysis of the relationship between the internal structures and the process performance of the austenitic Fe-Mn-Al-C low-density high-strength steel.

2) The metallographic corrosive disclosed by the invention is simple in operation steps for corrosion, and the working efficiency is improved.

Drawings

FIG. 1 is a metallographic structure under a metallographic microscope of 100 times after metallographic etching using the sample of example 1;

FIG. 2 is a metallographic structure drawing under a 500-fold metallographic microscope after metallographic etching using the sample of example 2;

FIG. 3 is a metallographic structure diagram under a 500-fold metallographic microscope of the sample in comparative example 1 after metallographic corrosion.

Detailed Description

The invention is further described in detail below with reference to the drawings and examples, but the invention is not limited in any way, and any changes or modifications made based on the teachings of the invention fall within the scope of the invention.

The invention relates to a metallographic corrosive agent for austenitic Fe-Mn-Al-C series low-density high-strength steel, which comprises picric acid, ferric chloride, concentrated hydrochloric acid and absolute ethyl alcohol, and the mixture ratio of the metallographic corrosive agent is as follows: 1-3g of picric acid, 2-6g of ferric trichloride, 4-6ml of concentrated hydrochloric acid and 80-100ml of absolute ethyl alcohol.

The picric acid, the ferric trichloride and the absolute ethyl alcohol are all commercially available analytical pure products, and the concentrated hydrochloric acid is a commercially available analytical pure product and has the concentration of 36-38%.

The preparation method of the metallographic corrosive agent comprises the following steps:

1) adding picric acid into part of anhydrous ethanol, and dissolving to obtain a mixed solution a;

2) adding ferric chloride into the mixed solution a, and stirring to completely dissolve the ferric chloride to form mixed solution b;

3) adding the residual absolute ethyl alcohol into the mixed solution b to prepare a mixed solution c;

4) and pouring concentrated hydrochloric acid into the mixed solution c, uniformly stirring, and standing for 3-5 minutes to ensure the uniformity of the corrosive liquid to obtain the target corrosive.

Heating absolute ethanol to 40-50 deg.C, adding picric acid, and stabilizing the dissolving speed of picric acid to make the concentration of picric acid in the corrosive agent in a stable and controllable range;

cooling the mixed solution c to room temperature, and then adding concentrated hydrochloric acid.

In order to control the volatilization degree of the absolute ethyl alcohol in the heating process and ensure the picric acid concentration in the corrosive agent, in the step 1, only part of the absolute ethyl alcohol is used for dissolving the picric acid, and the added volume is 1/3-1/2 of the total volume.

The application of the metallographic corrosive agent in the metallographic corrosion of austenitic Fe-Mn-Al-C low-density high-strength steel is characterized in that the metallographic corrosive agent is dipped and wiped on the polished surface of a sample to be tested until the color of the polished surface is grayed, and then the polished surface is cleaned and dried.

And (3) carrying out coarse grinding, fine grinding, polishing, cleaning and drying on the sample to be tested before corrosion to obtain a bright and scratch-free sample surface.

The metallographic corrosive agent is heated to 30-40 ℃ and then dipped and wiped on a sample to be detected.

The time for wiping the sample to be tested by the metallographic corrosive agent is 5-10 s.

The cleaning mode is as follows: and (4) flushing the corroded sample to be detected with running water for 4-5 s.

The drying mode is as follows: and blowing the surface of the test sample by using a hair dryer until no water stain exists so as to prevent residual water from adhering to the surface of the test sample after the test surface is washed to influence metallographic observation.

The present invention is further illustrated by the following examples.

Example 1

A. Sample pretreatment: coarse grinding, fine grinding, polishing, cleaning and drying a low-density high-strength steel (the mass percent of each element is Mn 29 percent, Al 8 percent, C1 percent and the balance is Fe) sample to obtain a bright and scratch-free sample surface;

B. preparing an etchant: heating 50ml of absolute ethyl alcohol to 40 ℃, adding 1g of picric acid, adding 2g of ferric trichloride after dissolution, stirring to completely dissolve the mixture, adding 50ml of absolute ethyl alcohol to obtain a mixed solution, cooling the mixed solution to room temperature, pouring 5ml of hydrochloric acid into the mixed solution, stirring uniformly, and standing for 3 minutes to obtain a corrosive agent;

C. and (3) corrosion operation: and heating the prepared corrosive agent to 30 ℃, dipping the corrosive agent, wiping the polished surface for 5s, and finishing corrosion after the color of the surface of the sample is observed to be grayed. After washing the sample for 4s with running water, blowing the surface of the detection surface of the sample by using an electric blower until no water stain exists;

D. and (3) metallographic structure observation: and (3) under a metallographic microscope with the magnification of 100 times, adjusting the brightness and the contrast of the picture, and taking a metallographic structure picture, wherein the metallographic structure picture is shown in a figure 1.

As can be seen from fig. 1, the metallographic structure of the sample to be measured in the embodiment is clear and complete, the observation and the rating of the metallographic structure are not affected by the color and the morphology, and the morphology of the twin austenite and the morphology of the high-temperature alpha ferrite in the discontinuous chain-like distribution can be clearly observed.

Example 2

A. Sample pretreatment: carrying out coarse grinding, fine grinding, polishing, cleaning and drying on a low-density high-strength steel (the mass percentage of each element is Mn 29%, Al 8%, C1% and the balance is Fe) metallographic specimen to obtain a bright and scratch-free specimen surface;

B. preparing an etchant: firstly heating 50ml of absolute ethyl alcohol to 50 ℃, dissolving 3g of picric acid in the heated absolute ethyl alcohol, then adding 6g of ferric trichloride, stirring to completely dissolve the ferric trichloride, then adding 50ml of absolute ethyl alcohol to form a mixed solution, cooling the mixed solution to room temperature, pouring 5ml of hydrochloric acid into the mixed solution, uniformly stirring, and standing for 5 minutes to obtain a corrosive agent;

C. and (3) corrosion operation: and heating the prepared corrosive agent to 40 ℃, dipping the corrosive agent, wiping the polished surface for 10s, and finishing corrosion after the color of the surface of the sample is observed to be grayed. Washing the sample for 5s by using running water, and finally blowing the surface of the detection surface of the sample by using an electric blower until no water stain exists;

D. and (3) metallographic structure observation: and (3) under a metallographic microscope with the magnification of 500 times, adjusting the brightness and the contrast of the picture, and taking a metallographic structure picture, wherein the metallographic structure picture is shown in a figure 2.

As can be seen from FIG. 2, the metallographic structure of the sample to be measured in the embodiment is clear and complete, the observation and the rating of the metallographic structure are not affected by the color and the morphology, and the morphology of twin austenite and k-carbide precipitates precipitated along grain boundaries can be clearly observed. 15-30% of Mn; 2-12% of Al; c is greater than 0.5%; the balance being Fe.

Example 3

A. Sample pretreatment: coarse grinding, fine grinding, polishing, cleaning and drying a low-density high-strength steel (the mass percent of each element is 15 percent of Mn, 12 percent of Al, 2 percent of C and the balance of Fe) sample to obtain a bright and scratch-free sample surface;

B. preparing an etchant: heating 50ml of absolute ethyl alcohol to 45 ℃, adding 2g of picric acid, adding 4g of ferric trichloride after dissolution, stirring to completely dissolve the mixture, adding 50ml of absolute ethyl alcohol to obtain a mixed solution, cooling the mixed solution to room temperature, pouring 4ml of hydrochloric acid into the mixed solution, stirring uniformly, and standing for 4 minutes to obtain a corrosive agent;

C. and (3) corrosion operation: and heating the prepared corrosive agent to 35 ℃, dipping the corrosive agent, wiping the polished surface for 5s, and finishing corrosion after the color of the surface of the sample is observed to be grayed. Washing the sample with running water for 4s, washing with absolute ethyl alcohol for 2-3s, and blowing the sample in the same direction by an electric blower;

D. and (3) metallographic structure observation: and observing the metallographic structure under a metallographic microscope.

Example 4

A. Sample pretreatment: coarse grinding, fine grinding, polishing, cleaning and drying a low-density high-strength steel (the mass percent of each element is Mn 24%, Al 2%, C1.5% and the balance is Fe) metallographic specimen to obtain a bright and scratch-free specimen surface;

B. preparing an etchant: heating 50ml of absolute ethyl alcohol to 42 ℃, dissolving 2g of picric acid in the heated absolute ethyl alcohol, adding 5g of ferric trichloride, stirring to completely dissolve the ferric trichloride, adding 50ml of absolute ethyl alcohol to form a mixed solution, cooling the mixed solution to room temperature, pouring 6ml of hydrochloric acid into the mixed solution, stirring uniformly, and standing for 5 minutes to obtain a corrosive agent;

C. and (3) corrosion operation: and heating the prepared corrosive agent to 38 ℃, dipping the corrosive agent, wiping the polished surface for 10s, and finishing corrosion after the color of the surface of the sample is observed to be grayed. Washing with running water for 4s, and blow-drying with electric blower;

D. and (3) metallographic structure observation: and observing the metallographic structure under a metallographic microscope.

Comparative example 1

A. Sample pretreatment: carrying out coarse grinding, fine grinding, polishing, cleaning and drying on a low-density high-strength steel (the mass percentage of each element is Mn 29%, Al 8%, C1% and the balance is Fe) metallographic specimen to obtain a bright and scratch-free specimen surface;

B. and (3) corrosion operation: etching the test sample in 4% nitric acid absolute ethyl alcohol for 10s, taking out the test sample, washing and drying the test sample by using clear water, and etching the test sample in 6% hydrochloric acid absolute ethyl alcohol for 10 s;

C. and (3) metallographic structure observation: and (3) under a metallographic microscope with the magnification of 500 times, adjusting the brightness and the contrast of the picture, and taking a metallographic structure picture, wherein the metallographic structure picture is shown in figure 3.

In fig. 3, the twin austenite grain boundaries of the comparative example can be more clearly shown. However, the high-temperature alpha ferrite is easily confused with a twin crystal line in twin crystal austenite and is difficult to distinguish, and a k-carbide precipitate structure precipitated along a grain boundary is not shown, so that the method cannot be used for analyzing the relation between the internal structure and the process performance of the austenitic Fe-Mn-Al-C series low-density high-strength steel.

And (4) analyzing results: comparing the metallographic structure diagrams of the samples of the examples 1 and 2 and the sample of the comparative example 1, the metallographic corrosive agent disclosed by the invention can clearly and completely display the structures of austenite, high-temperature alpha ferrite and k-carbonized precipitates in the austenitic Fe-Mn-Al-C series low-density high-strength steel by corroding the low-density high-strength steel (the mass percentages of all elements are Mn 24%, Al 2%, C1.5% and the balance of Fe) by using the metallographic corrosive agent disclosed by the invention, and is superior to the prior art and simpler to operate.