Hello.
I'm looking for an etching that will well show the grain size without
revealing the martensitic needles.
The stainless steel is Z12CNDV12 or 1.4939 or UNS K64152 or ASTM A565.
Thanks for your help.
All the best.
Adrien
In the hardenend state, only martensite gain boundaries exist. How
should an etchant know, which grain boundary is a former austenite grain
boundary and which one is newly formed?
In order to detect the former austenite grain size, you need either
advanced image processing or Brain 1.0.
Michael Dahms
Michael:
The prior austenite grains can be delineated in alloy steels if there
is phosphorus segregation present. Temper embrittlement etchants have
been known for the last fifty years, and continue to be discussed.
For example, see Van der Voort's Practical Metallography, or more
specifically:
L=2E Zhang & D. Guo
Materials Characterization ; Vol/Issue: 30:4 June 1993
A general etchant for revealing prior-austenite grain boundaries in
steels
In development of effective etchants for revealing the prior-austenite
grain boundaries in steels of different composition, microstructure and
properties are of significant importance in many areas, for example, in
the development of new alloys, in structure-property correlations, in
steel quality evaluations, and in failure analysis. At present, the
Bechet-Beaujard etching solution is the most successful etchant for the
delineation of prior-austenite grain boundaries in hardened steels. It
is most useful for medium-and high-carbon alloy steels but does not
work if the phosphorus content is very low. The authors have developed
a CrO[sub 3]-NaOH-picric acid etchant that does not require preheating
of the specimen, although the etchant still must be heated. Results
indicate that this etch has a wide degree of applicability regarding
steel compositions, heat treatments, and microstructures.
Pittsburgh Pete
Thanks! You are right, segregations can certainly enhance etching.
| It is most useful for medium-and high-carbon alloy steels but does not
| work if the phosphorus content is very low.
Just curious: What is meant by 'very low'? Actual high-quality steels
tend to have a very low phosphorous content. (1.4939, P < 0.025%)
Michael Dahms
So I have to use the Bechet-Beaujard etchant to see the grain
boundaries the best. Thanks for the informations.
I'm working as a student in a laboratory and have to find an etching
for the Z12CNDV12. The laboratory does not have CrO[sub3] in stock, can
I replace it by something else?
Kind regards.Adrien.
The XM-32 martensitic stainless steel may not respond to the reagent I
described. Thermal etching is another possibility. My best advice is
to look in the literature on metallography, or to contact some
stainless steel producers to see what they use. Two specialty magazines
to check are Materials Characterization and Practical Metallography.
G. F. Vander Voort, "Wetting Agents in Metallography," Materials
Characterization, Vol. 35, No. 2, Sept 1995, p. 135-7
W. Brewer, K. A. Erven, and G. Krauss, "Etching and Image Analysis of
Prior Austenite Grain Boundaries in Hardened Steels," Materials
Characterization, Vol. 27, No. 1, 1991, p. 53-56
C. Garcia de Andres et al., "Revealing Austenite Grain Boundaries by
Thermal Etching,: advantages and Disadvantages," Materials
Characterization, Vol. 49, No. 2, 2002, p. 121-7
E. Schacht & J. Richter, "Experiences with Etching Reagents to Show
Former Austenite Grain Boundaries in Steels ," Practical
Metallography, July 1998
Go to
formatting link
for Materials Characterization
The Practical Metallography Archive is at:
The XM-32 martensitic stainless steel may not respond to the reagent I
described. Thermal etching is another possibility. My best advice is
to look in the literature on metallography, or to contact some
stainless steel producers to see what they use. Two specialty magazines
to check are Materials Characterization and Practical Metallography.
G. F. Vander Voort, "Wetting Agents in Metallography," Materials
Characterization, Vol. 35, No. 2, Sept 1995, p. 135-7
W. Brewer, K. A. Erven, and G. Krauss, "Etching and Image Analysis of
Prior Austenite Grain Boundaries in Hardened Steels," Materials
Characterization, Vol. 27, No. 1, 1991, p. 53-56
C. Garcia de Andres et al., "Revealing Austenite Grain Boundaries by
Thermal Etching,: advantages and Disadvantages," Materials
Characterization, Vol. 49, No. 2, 2002, p. 121-7
E. Schacht & J. Richter, "Experiences with Etching Reagents to Show
Former Austenite Grain Boundaries in Steels ," Practical
Metallography, July 1998
Go to
formatting link
for Materials Characterization
The Practical Metallography Archive is at:
The company I work for manufactures this alloy, known as Jethete M152, etc.
Our standared etch for Grain size is picric acid as described in a previous
posting. Please be aware that it does conatin hexa-valent chromium which is
banned in some countries. I think an alternative would be 2 to 5% 'Nital'
(Nitric acid in ethanol or similar). I will ask our lab technicians and
check this for you.
Andrew Kirton-Vaughan
I could try this morning the Bechet Beaujard etchant with no success.
I used 60mL NaOH, 5gr of picric acid and some CrO3 that I didn't
weight.
I heated this mixture and placed the sample in it. After a long time
(20minutes) there weren't any effect on the steel that was still like a
mirror as when I polished it.
I could try these days many many differents etchants and could find
that the most efficient one is a "custom" one: 20mL hydrochloridric
acid, 10mL nitric acid and 60mL ethanol for 5/10minutes. It worked
quite good but I'd like better again and again.
I can't wait for the reply from your lab technicians Andrew K-V :)
Kind regards.
Adrien.
Andrew K-V wrote:
Hi,
Chatted to our lab guys. Recomendations:
Vilella's Reagent: 1g Picric Acid
5ml HCl
100ml Ethanol
Ferric Chloride: 10 g Ferric Chloride
30 ml HCl
120 ml Water
Kallings Solution: 5 g Cupric Chloride
100ml Methanol
100ml Water
10ml Nitric Acid
Unnammed solution: 45ml Glycerol
15ml Nitric Acid
30ml Hydrochloric Acid
Recommend Vilella's for a start, the try acidic ferric chloride. The last
solution is best for austenitic stainless steels like 304 and 316 and is
very, very quick to etch.
Hope this helps
Andrew
For stainless steel alloys that are difficult to etch, electrolytic ething
can sometimes be helpful.
In the past I have used 10% oxalic acid in water at 5 volts, making the
microsection the anode and using a piece of any austenitic staimless steel
the cathode. (You can make the micro the anode by using a sharp stainless
steel probe connected to the positive DC supply to make a point contact).
Other electrolyes can sometimes work, including ammonium persulphate, lactic
acid or chromic acid.
The etching time can vary between 5 seconds and 2 minutes. Trial and error
is needed but the electrolytic method is often better than plain chemical
methods for stainless steels.
I hope something along these lines will be useful,
Good luck,
Roger
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