Klemm's I is the most powerful etch to color ferrite, but if other constituents are present, you cannot tell them apart. Aqueous 10% sodium metabisulfite is a very good color etch for mixed microstructures. It does not color ferrite grains much but martensite is colored brown and bainites are blue and white (varying a bit between upper and lower bainite). It does not color cementite. Pearlite can be seen as the ferrite between the cementite will be colored. To color cementite use alkaline sodium picrate at ~90 C. I swab the specimen for ~20 s then wash, dry and check the results. If inadequate, swab again for another 20 s and check the results. Usually no more than 60 s total is required.

Cheers, I am using LePera to some extent, for bainite mostly. But I am also not quite satisfied, especially for CP structures. V.

hello, I think potassium metabisulfide 10% is very good (potassium metabisulfide + 100 ml distiiled water). good luck.

When using Le Pera as anodic colour tint etchant - carbon enriched areas remains white or brighter. Conversely, when using for example Lichtenegger-Bloech etchant (cathodic colour tint etchant) anodic areas with less or no carbon remain white or brighter. Ferrite contains less carbon than austenite/martensite . Bainite contains less carbon than martensite. In my opinion, prior selective (attack) etching increases the quality of the colour etch.

@Hannes Pahr what do you recommend for prior selective attack? Before LePera. Many thanks in advance.

Nital or Picric Acid (Villela's Reagent); very shortly...

Many thanks for your valuable inputs Hannes Pahr Vratko Vokál Soroush Bakhshi , I am trying different permutations with post-validation using higher magnification scanning electron microscopy. Hopefully, something good will come out. It will be helpful if some of you can throw light on the desirable range of saturation and polarized light as the tint is greatly affected by changing these parameters. Thanks again!

Hallo dear all ...

I willa dvice relevant and excellent paper from Prof Mücklich, Germany and his team as ...

britz d, steimer y, mücklich f,

„a new approach for color metallography: through controlled conditions to objective microstructure analysis of low carbon steels by LePera-Etching“,

100 years of E04 development of metallography standards, ASTM STP1607,

G F Vander Voort, Ed., ASTM International, west conshohocken, PA,

2019, pp 130-151,

http://dx.doi.org/10.1520/STP160720170242

this paper includes extensive review of the subject (which is very helpful for basic understanding)...and experimental description for professional lab solution to apply LePera etchant.

best regards

Johann Angeli

... and due to the fact that color etchant need higer ptential differences between the microconstituets to differentiate,

so in ahss grades mostly M/RA phase will be able to differentiate from ferrite matrix...bainte is ferrite + carbides or M/RA films/islands.... tempered martensite makes it also not easy anymore...

pls try nital etchant and FE-SEM...nitals develops finest microstructures ..with some experience you will be able also to distinguish the phase you mentioned in your question, based on their morphology developed due to the structure etchant nital. if you apply picral instead of nital you will not be able to differentiate in that detaisl.

picral develops mainly phase with higher electrochemical potentials vs ferrit = this means it is good for carbide morphologies

best regards

Klemm's I is the most powerful etch to color ferrite, but if other constituents are present, you cannot tell them apart. Aqueous 10% sodium metabisulfite is a very good color etch for mixed microstructures. It does not color ferrite grains much but martensite is colored brown and bainites are blue and white (varying a bit between upper and lower bainite). It does not color cementite. Pearlite can be seen as the ferrite between the cementite will be colored. To color cementite use alkaline sodium picrate at ~90 C. I swab the specimen for ~20 s then wash, dry and check the results. If inadequate, swab again for another 20 s and check the results. Usually no more than 60 s total is required.

Use Bereha's potassium metabisulphide reagent, please refer my papers (underwater welding especially)....

Dear Sr. I'm using LePera..

My 1st preference to try is aqueous 10% sodium metabisulfide. I recently saw an article on this subject by metallographers in Iran (attached) which may be of interest to you. I have attached some additional examples of the use of 10% SMB. Good luck!

George

Thank you sir.

You are most welcome! Good luck!

I have used the aqueous solutions of sodium metabisulfite in cast irons and steels with mixed microstructures and they always work very well, as suggested by Sir Vander Voort. They are simple to prepare and use, as well as provide the microstructure revelation as a function of the immersion time in an easy to control manner. By making short successive etchings and subsequent observations in the microscope, you can observe what is being revealed before and how the reagent reveals each microconstituent. Good Job!

Pre-etching with Nital %2 for 2 s and then etching with 10% Sodium Metabisulfite will be useful.

A two step electro etching was introduced by Ikawa et al., where first the ferrite matrix is etched ( EDTA 5g, NaF 0.5g and distilled water 100ml) while the micro phases (including carbides and austenite-martensite constituents) remain un-etched. In the second stage the carbides get etched (picric acid 5g, NaOH 25g and distilled water 100ml) while the martensite-austenite constituents remained un etched. This proved to be very effective for SEM investigations but I had problems with LOM. That is teh surface is so deeply etched that a good image cannot be obtained with LOM depth of focus.

So I used a modified version; In this two step etching, first the surface is electrolitically etched using EDTA-NaF mixture (as explained before). A next step of etching is done by immersing in Le Pera, leading to a generally yellowish ferrite , grey to black carbides (tempered zones, carbide aggregates) and white patches of martensite/Austenite constituents.