What is a good grain boundary etchant for heat treated  martensitic steels and stainless steels to determine the grain size?  Typical etchants show the martensitic structure which obscures the grain boundaries.

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Russell Cochran
Associate Technical Fellow
Boeing
Maryland Heights MO
(314) 283-5342
------------------------------

Hi Russell

I have been trying to get this information as well. I have seen research papers use EBSD to figure out the prior austenite grain size but have not come across etchant to reveal prior austenite grain boundaries. It would be helpful to get this information. 

Regards
Rajan

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Rajan Bhambroo
Materials Engineer
Tenneco Inc
Plymouth MI
7346600894
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You might try the IMS members at www.metallography.com. Many questions and answers about metallography sample prep can be found here, including etchant recommendations.

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David Fitzgerald
President
Precision Surfaces Intl. Inc.,Precision Surfaces International
Houston TX
------------------------------

Russell, we have written many articles on 304Cu stainless steel with two different grain size. To assess grain size, we used: Electrolitic preparation effected with Struers A2 reactant, followed by electrolitic etching by oxalic acid (10% concentration), duration 1 min.

------------------------------
Donato FIRRAO FASM
Professor
Politecnico di Torino
TORINO
+393351494032
Italy
------------------------------

Original Message:
Sent: 4/7/2023 2:28:00 PM
From: Donato FIRRAO
Subject: RE: Grain boundary etchant

Russell, we have written many articles on 304Cu stainless steel with two different grain size. To assess grain size, we used: Electrolitic preparation effected with Struers A2 reactant, followed by electrolitic etching by oxalic acid (10% concentration), duration 1 min.

------------------------------
Donato FIRRAO FASM
Professor
Politecnico di Torino
TORINO
+393351494032
Italy
------------------------------

Dear Russell,
sorry for the delay in the response, due to Easter's holidays in my university.
You may try the oxalic acid electrolytic etch for martensitic stainless steels as well. It should be able to emphasize prior austenitic grain boundaries also in this case. Given the lower corrosion resistance of martensitic stainless steel in respect to austenitic ones, you should keep the etch intensity at a lower level.

------------------------------
Donato FIRRAO FASM
Professor
Politecnico di Torino
TORINO
+393351494032
Italy
------------------------------

Original Message:
Sent: 04-07-2023 16:02
From: Russell Cochran
Subject: Grain boundary etchant

I am familiar with the electrolytic oxalic acid for etching grain boundaries of 300 series austenitic CRES.  However, my problem is with martensitic steels and martensitic stainless steels.  Or do you think that would work for the martensitic alloys also?

 

Cheers,

Russ

 

Original Message:
Sent: 4/7/2023 2:28:00 PM
From: Donato FIRRAO
Subject: RE: Grain boundary etchant

Russell, we have written many articles on 304Cu stainless steel with two different grain size. To assess grain size, we used: Electrolitic preparation effected with Struers A2 reactant, followed by electrolitic etching by oxalic acid (10% concentration), duration 1 min.

------------------------------
Donato FIRRAO FASM
Professor
Politecnico di Torino
TORINO
+393351494032
Italy
------------------------------

What about martensitic alloy and carbon steel that have been quench and tempered.  Do you know of an prior austenitic grain boundary etchant for that? I never heard back from Buehler.

------------------------------
Russell Cochran
Associate Technical Fellow
Boeing
Maryland Heights MO
(314) 283-5342
------------------------------

Original Message:
Sent: 04-11-2023 16:04
From: Donato FIRRAO
Subject: Grain boundary etchant

Dear Russell,
sorry for the delay in the response, due to Easter's holidays in my university.
You may try the oxalic acid electrolytic etch for martensitic stainless steels as well. It should be able to emphasize prior austenitic grain boundaries also in this case. Given the lower corrosion resistance of martensitic stainless steel in respect to austenitic ones, you should keep the etch intensity at a lower level.

------------------------------
Donato FIRRAO FASM
Professor
Politecnico di Torino
TORINO
+393351494032
Italy
------------------------------


Original Message:
Sent: 04-07-2023 16:02
From: Russell Cochran
Subject: Grain boundary etchant

I am familiar with the electrolytic oxalic acid for etching grain boundaries of 300 series austenitic CRES.  However, my problem is with martensitic steels and martensitic stainless steels.  Or do you think that would work for the martensitic alloys also?

 

Cheers,

Russ

 

Original Message:
Sent: 4/7/2023 2:28:00 PM
From: Donato FIRRAO
Subject: RE: Grain boundary etchant

Russell, we have written many articles on 304Cu stainless steel with two different grain size. To assess grain size, we used: Electrolitic preparation effected with Struers A2 reactant, followed by electrolitic etching by oxalic acid (10% concentration), duration 1 min.

------------------------------
Donato FIRRAO FASM
Professor
Politecnico di Torino
TORINO
+393351494032
Italy

Dear Russell,

Back in the day when I was researching for my DPhil I was looking at stress corrosion and hydrogen embrittlement in a controlled transformation stainless steel, specifically the effect of retained austenite. This turned out to be a problem because the mill that rolled the steel for me did not homogenise it so I was effectively looking at a fibre composite. Be that as it may, one of the etches I was using for grain boundaries was Vilella's, one of the picric acid family. Indeed the ASM  metallography handbook recommends a range of picric acid etches. Of course, these upset lab safety officers but essentially you need a detonator to set picric acid off so lab sturage of small quantities is not a problem. 

I did not do any electrolytic etching because it wasn't necessary but did electropolish to prepare samples for selected area diffraction in the SEM (this is before the days of EBSD) and we used perchloric acid/glacial acetic acid/ethanol: now, that is dangerous if you mix in the wrong proportions and do not keep it chilled. It destroyed a factory during WWII.

Regards,
Peter Northover

------------------------------
Peter Northover
Retired
University of Oxford
+44 1865 820543
peter.northover@retired.ox.ac.uk
------------------------------

Original Message:
Sent: 04-11-2023 17:20
From: Russell Cochran
Subject: Grain boundary etchant

What about martensitic alloy and carbon steel that have been quench and tempered.  Do you know of an prior austenitic grain boundary etchant for that? I never heard back from Buehler.

------------------------------
Russell Cochran
Associate Technical Fellow
Boeing
Maryland Heights MO
(314) 283-5342
------------------------------


Original Message:
Sent: 04-11-2023 16:04
From: Donato FIRRAO
Subject: Grain boundary etchant

Dear Russell,
sorry for the delay in the response, due to Easter's holidays in my university.
You may try the oxalic acid electrolytic etch for martensitic stainless steels as well. It should be able to emphasize prior austenitic grain boundaries also in this case. Given the lower corrosion resistance of martensitic stainless steel in respect to austenitic ones, you should keep the etch intensity at a lower level.

------------------------------
Donato FIRRAO FASM
Professor
Politecnico di Torino
TORINO
+393351494032
Italy


Original Message:
Sent: 04-07-2023 16:02
From: Russell Cochran
Subject: Grain boundary etchant

I am familiar with the electrolytic oxalic acid for etching grain boundaries of 300 series austenitic CRES.  However, my problem is with martensitic steels and martensitic stainless steels.  Or do you think that would work for the martensitic alloys also?

 

Cheers,

Russ

 

Original Message:
Sent: 4/7/2023 2:28:00 PM
From: Donato FIRRAO
Subject: RE: Grain boundary etchant

Russell, we have written many articles on 304Cu stainless steel with two different grain size. To assess grain size, we used: Electrolitic preparation effected with Struers A2 reactant, followed by electrolitic etching by oxalic acid (10% concentration), duration 1 min.

------------------------------
Donato FIRRAO FASM
Professor
Politecnico di Torino
TORINO
+393351494032
Italy

Hi Russell,
Are you looking to reveal prior austenite grain boundaries or Austenitic grain boundaries after heat treatment (Q and T)? As your statement above, you are looking to find a grainsize after heat treatment.
Prior austenitic grain boundary test results come from steel mill and listed on the mill cert. For just a plan carbon Steel it is finer than ASTM 5 for alloyed steel it is finer than ASTM 8 (normally runs around ASTM  9-10). Let me know which one you are looking for.

Thanks,

------------------------------
Sanjay Kulkarni
Materials Engineer
MSSC
2040 Crooks RD, Suite A
Troy, MI 48084
sanjay.kulkarni@msscna.com
Cell: 248-840-1056
------------------------------

Hi Russell,
I spent many years in revealing grainsize of ferrous and non-ferrous alloys. For steel, I etch with 2% Nital followed by Picric Acid ACS. I keep it on the specimen surface with a small cotton ball for 5-6 hours. Rinse with Ethanol. Wipe the oxidized surface with dry cotton ball rinse again with Ethanol dry it with mount dryer. Avoid any water exposure through-out the process. This method was the only way I could get the results I wanted. See the screenshot of quench and tempered martensite of Alloy 5160H grainsize below. I am not sure which alloys you are using but it works for low carbon/high Mn boron steels also. 


Note: The small quantity of Picric Acid is not explosive. I am using it for many years. I do not keep the same bottle more than six months.

------------------------------
Sanjay Kulkarni
Materials Engineer
MSSC
2040 Crooks RD, Suite A
Troy, MI 48084
sanjay.kulkarni@msscna.com
Cell: 248-840-1056
------------------------------

Original Message:
Sent: 04-12-2023 10:01
From: Sanjay Kulkarni
Subject: Grain boundary etchant

Hi Russell,
Are you looking to reveal prior austenite grain boundaries or Austenitic grain boundaries after heat treatment (Q and T)? As your statement above, you are looking to find a grainsize after heat treatment.
Prior austenitic grain boundary test results come from steel mill and listed on the mill cert. For just a plan carbon Steel it is finer than ASTM 5 for alloyed steel it is finer than ASTM 8 (normally runs around ASTM  9-10). Let me know which one you are looking for.

Thanks,

------------------------------
Sanjay Kulkarni
Materials Engineer
MSSC
2040 Crooks RD, Suite A
Troy, MI 48084
sanjay.kulkarni@msscna.com
Cell: 248-840-1056
------------------------------

Russell,
For checking carbon steel parts, we have had good luck with ES Laboratories prior-austenite grain boundaries etch (http://www.eslaboratory.com/product.html). A 0.5 micron polish after etching makes the grain boundaries jump out at you. It's aggressive stuff, and sometimes doesn't make for the prettiest pictures, but it gets the job done.
The attached image is quenched and tempered 5046.
We tried a little bit of everything before we found this stuff.
I haven't tried it on stainless yet.

------------------------------
Edward White, P.E.
------------------------------

Dear Russell, in our multiple researches on Q+T die steels (mostly 1.2738 steel -ISO 4957), the previous austenitic grains boundaries (PAGB) were visualized by the Bechet-Beaujard etch, an etchant containing saturated aqueous picric acid and 0.5% sodium alkyl-sulfonate (a wetting agent). Krauss also suggests etching with an aqueous solution saturated with picric acid and containing sodium tridecylbenzene sulfonate, with small additions of HCl, as one of the most effective techniques to reveal PAGBs in hardened steels. A quite recent review can be found in "Sinha, V., Payton, E.J., Gonzales, M. et al. Delineation of Prior Austenite Grain Boundaries in a Low-Alloy High-Performance Steel. Metallogr. Microstruct. Anal. 6, 610–618 (2017).

------------------------------
Donato FIRRAO FASM
Professor
Politecnico di Torino
TORINO
+393351494032
Italy
------------------------------

Original Message:
Sent: 04-13-2023 08:54
From: Edward White
Subject: Grain boundary etchant

Russell,
For checking carbon steel parts, we have had good luck with ES Laboratories prior-austenite grain boundaries etch (http://www.eslaboratory.com/product.html). A 0.5 micron polish after etching makes the grain boundaries jump out at you. It's aggressive stuff, and sometimes doesn't make for the prettiest pictures, but it gets the job done.
The attached image is quenched and tempered 5046.
We tried a little bit of everything before we found this stuff.
I haven't tried it on stainless yet.

------------------------------
Edward White, P.E.
------------------------------

Russell,

I think a cursory look in the ASM Handbook helps here as well. But also from experience, this is a pretty classical application case for Vilella's reagent. In general, combination of 2-5% HCl, 1-4g picric acid in ethanol should be all giving you a good etch result in less than a minute, depending on composition, aging condition etc.
The good thing about Vilella's is, that due its high HCl content, you can use if stainless steels as well.
Depending on what you want to highlight in the microstructure, there is Kalling's 1/2, Fry's, Spaeder's, Glyceregia of course, or Murakami's for getting into nice some dark color contrasting of phases. 
If you want to perform EBSD, I would go lighter in etch/shorter in time or even avoid altogether. Here, final polish in colloidal silica (pH 9) suffices for accentuation of GBs and relief, even for LOM use. 

Thanks
Ben

------------------------------
Benjamin Adam
Research Assistant Professor
Oregon State University
Corvallis OR
(503) 725-2996
------------------------------

Our facility in Germany uses VisiPro-1 Etchant from QATM for prior austenitic grain boundaries in steel. The description from QATM is as follows: VisiPro-I Etchant for visualizing the former austenitic grain boundaries (for quenched or tempered low-alloy quenched and tempered steels and case-hardened steels). They also have VisiPro-2: Etchant for visualizing the former austenitic grain boundaries (for quenched or tempered low-alloy quenched, tempered case hardening steels and anti-friction bearing steels). We have only tried VisiPro-1 once here in our US facility but it looks like it shows promise. We wanted to look for the prior austenitic grain size on some induction hardened medium carbon steel.

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Christopher Hensel
Material Science Engineer
Schaeffler Group USA
Fredericksburg OH
------------------------------

Russell, a recent article appeared on AMP journel with the suggestion of another technique for ferritic-martensitic stainless steel metallographic analysis.
The following article is recommended:

Improvements in the Metallography of Ferritic–Martensitic Steels Through a Color Etching Procedure

• Mantosh Mandal,
• B. Aashranth,
• Dipti Samantaray &
• M. Vasudevan 

Metallography, Microstructure, and Analysis volume 12, pages 49–61 (2023)

------------------------------
Donato FIRRAO FASM
Professor
Politecnico di Torino
TORINO
+393351494032
Italy
------------------------------

Original Message:
Sent: 04-20-2023 10:28
From: Christopher Hensel
Subject: Grain boundary etchant

Our facility in Germany uses VisiPro-1 Etchant from QATM for prior austenitic grain boundaries in steel. The description from QATM is as follows: VisiPro-I Etchant for visualizing the former austenitic grain boundaries (for quenched or tempered low-alloy quenched and tempered steels and case-hardened steels). They also have VisiPro-2: Etchant for visualizing the former austenitic grain boundaries (for quenched or tempered low-alloy quenched, tempered case hardening steels and anti-friction bearing steels). We have only tried VisiPro-1 once here in our US facility but it looks like it shows promise. We wanted to look for the prior austenitic grain size on some induction hardened medium carbon steel.

------------------------------
Christopher Hensel
Material Science Engineer
Schaeffler Group USA
Fredericksburg OH
------------------------------

I tend to use 3-4 parts HCl to 1 part H2O2

It will only take seconds, immersion is better, but swab works. The solution will turn yellow telling you it's ready to rinse.

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Christopher Crouse
Senior Materials Engineer
Woodward Inc.
Fort Collins CO
9703023451
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