What etching for ASTM A565 stainless steel?

What is the 'grain size' of martensite?

Michael Dahms

Michael Dahms a =E9crit :

Actually, I'd like only to see the austenitic grains rather than seeing the martensite.

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

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

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 :)

K> The company I work for manufactures this alloy, known as Jethete M152, etc.

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

Oxidize it per astm e112