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Metallographic Cast Iron Etchants

The most common etchants for cast irons is 2% Nital, however, a good resouce for additional etchants can be found with the etchant database provided by PACE Technologies

PACE Technologies Etchant Database Click here to get order

CAUTION: Safety is very important when etching. Be sure to wear the appropriate protective clothing and observe all WARNINGS on chemical manufacuters SDS (Safety Data Sheets). Also review the COMMENTS and CONDITIONS Section for each etchant.

Sample Preparation:
Cast Irons are difficult materials to prepare properly because the graphite nodules or the graphite flakes are easily fractured and pulled out during preparation. By minimizing the sectioning damage and starting with a modest grit size SiC paper, retaining these difficult particles can be accomplished.

PACE Technologies Recommended Preparation for brass and bronze alloys PACE Technologies Metallographic MET-MANUAL Link
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Recommended Etchants
Etchant Conc. Conditions Comments
Nitric acid

100 ml
1-10 ml
Seconds to minutes Do not exceed 10% nitric acid -explosive
Saturated sodium thiosulfate
Potassium metabisulfite

250 ml
25 grams
Seconds to minutes Dual phase tint etchant. Ferrite is light or dark blue, martensite brown and black, retained austenite white. Heating to 40°C will enhance the staining

Metallographic micrograph of etched nodular cast iron
Nodular Cast Iron, 2% Nital,, 100X (DIC)
Metallographic micrograph of tint etched with Klemm's gray cast iron
Gray Cast Iron, Klemms 2 tint etch, 40°C, 1000X (BF).
Blue is ferrite, brown is martensite, austenite is white

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