Common Etchants for Iron and Steel

Composition	Comments
90-99 mL methanol or ethanol 1-10 mL HNO3	Nital. Most common etchant for Fe, carbon and alloy steels, cast iron. Reveals alpha grain boundaries and constituents. Excellent for martensitic structures. The 2% solution is most common, 5-10% used for high alloy steels (do not store). Use by immersion or swabbing of sample for up to bout 60 seconds.
1 00 mL ethanol 4 g picric acid	Picral. Recommended for structures consisting of ferrite and carbide. Does not reveal ferrite grain boundaries. Addition of about 0.5-1% zephiran chloride improves etch rate and uniformity.
100 mL ethanol 5 mL HCI 1 g picric acid	Vilella’s reagent. Good for ferrite-carbide structures. Produces grain contrast for estimating prior austenite grain size. Results best on martensite tempered at 572-932 °F (300-500 °C). Occasionally reveals prior-austenite grain boundaries in high alloy steels. Outlines constituents in stainless steels. Good for tool steels and martensitic stainless steels.
Saturated aqueous picric acid solution grain plus small amount of a wetting agent	Bechet and Beaujard’s etch, Most successful etchant for prior-austenite boundaries. Good for martensitic and bainitic steels. Many wetting agents have been used, sodium tridecylbenzene sulfonate is one of most successful (the dodecyl version is easier to obtain and works as well). Use at 20-100 °C. Swab or immerse sample for 2-60 minutes. Etch in ultrasonic cleaner Additions of 0.5g CuCl2 per 100mL solution or about 1% HCI have been used for higher alloy steels to produce etching. Room temperature etching most common. Lightly back polish to remove surface smut.
150 mL water 50 mL HCI 25 mL HNO3 1 g CuCl2	Modified Fry’s reagent. Used for 18% Ni maraging steels, martensitic and PH stainless steels.
1 00 mL water 25 g NaOH 2 g picric acid	Alkaline sodium picrate. Best etch for McQuaid-Ehn carburized samples. Darkens cementite. Use boiling for 1-15 minutes or electrolytic at 6 V dc, 0.5 A/in2, 30-120 seconds. May reveal prior-austenite grain boundaries in high carbon steels when no apparent grain boundary film is present.
1 00 mL ethanol 100 mL HCI 5 g CuCl2	Kalling’s no. 2 (“waterless” Kalling’s) Etch for austenitic and duplex stainless steels. Ferrite attacked readily, carbides unattacked, austenite slightly attacked. Use at 20 °C by immersion or swabbing. Can be stored.
1 5 mL HCI 10 mL acetic acid 5 mL HNO3 2 drops glycerol	Acetic glyceregia. Mix fresh; do not store. Use for high alloy stainless steels.
100 mL water 10 g K2Fe(CN)6 10 g KOH or NaOH	Murakami’s reagent. Usually works better on ferritic stainless grades than on austenitic grades. Use at 20 °C for 7-60 seconds: reveals carbides sigma faintly attacked with etching up to 3 minutes. Use at 80°C (176°F) to boiling for 2-60 minutes: carbides dark, sigma blue (not always attacked), ferrite yellow to yellow-brown, austenite unattacked. Do not always get uniform etching.
100 mL water 1 0 g oxalic acid	Use for stainless steels at 6 V dc. Carbides revealed by etching for 15-30 seconds, grain boundaries after 45-60 seconds, sigma outlined after 6 seconds. 1-3 V also used. Dissolves carbides, sigma strongly attacked, austenite moderately attacked, ferrite unattacked.
100 mL water 20 g NaOH	Used to color ferrite in martensitic, PH or dual-phase stainless steels. Use at 3-5 V dc, 20°C, 5 seconds, stainless steel cathode. Ferrite outlined and colored tan.
40 mL water 60 mL HNO3	Electrolytic etch to reveal austenite boundaries but not twin boundaries in austenitic stainless steels (304, 316, etc.). Voltage is critical. Pt cathode preferred to stainless steel. Use at 1.4 V dc, 2 minutes.