Stainless Steel Etchants

Guide to etching austenitic, martensitic, duplex, and precipitation hardening stainless steels. Covers Adler’s, Carpenter, Kalling’s, Murakami’s, and color etchants with compositions and applications.

Stainless Steel Prep Guide Etchant Catalog

Classification & Preparation

Stainless steels are challenging to etch due to their corrosion resistance. Austenitic grades are hardest to etch; martensitic grades are easier.

Stainless Steel Types

Major stainless steel families by microstructure.

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300 Series (Austenitic): 18% Cr, 8% Ni – Excellent corrosion resistance, non-magnetic
400 Series (Martensitic): Higher carbon – Heat treatable, magnetic
200 Series (Austenitic): Mn and N – Cost-effective alternative to 300
Duplex: Austenite + ferrite – Superior strength and corrosion resistance
Precipitation Hardening: Special heat treatment – High strength

Etching Considerations

Key factors for successful stainless steel etching.

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Austenitic grades require more aggressive etchants than martensitic
Monitor carefully to prevent over-etching sensitive grades like 316L
Use specialized etchants for welded samples to reveal HAZ
Murakami’s reagent identifies sigma phase in duplex grades
Electrolytic etching ensures uniform results on large samples

Preparation Tips

Proper surface preparation is essential for consistent etching results.

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Ensure proper surface preparation before etching
Choose etchant based on grade and desired features
Store etched samples in dry environment
Prepare fresh etchants for each use

Recommended Etchants

For PACE's full etchant catalog and the Materials Prep ELN, see Etchant Resources.

Etchant	Composition	Conditions	Applications
Adler’s Etchant	Ferric chloride: 45 g Copper ammonium chloride: 9 g Hydrochloric acid: 150 ml Distilled water: 75 ml	Immerse for several seconds	300 series, austenitic, duplex stainless steels
Carpenter Etchant	Ferric chloride: 8.5 g Cupric chloride: 2.4 g Alcohol: 122 ml Hydrochloric acid: 122 ml Nitric acid: 6 ml	Immerse for several seconds	300 series, austenitic, duplex stainless steels
Kalling’s No. 2 (Waterless)	Cupric chloride: 5 g Hydrochloric acid: 100 ml Ethanol or methanol: 100 ml	Immerse or swab Seconds to minutes at 20°C	400 series / martensitic stainless steels Also used for duplex and Ni-Cu superalloys
Vilella’s Reagent	Picric acid: 1 g Hydrochloric acid: 5 ml Ethanol: 100 ml	Immerse or swab for seconds to minutes Rinse in water Dry with alcohol	Martensitic and precipitation-hardening stainless steels Reveals prior austenite grain boundaries and ferrite-carbide structures WARNING: picric acid is explosive when dry. Keep solution hydrated
Modified Murakami’s	K₃Fe(CN)₆: 30 g Potassium hydroxide: 30 g Distilled water: 150 ml	1 second to several minutes Immersion or swabbing	Mix KOH into water before adding K₃Fe(CN)₆
Color Etchant	Hydrochloric acid: 20–30 ml Selenious acid (H₂SeO₃): 1–3 ml Ethyl alcohol: 100 ml	Immerse at room temperature 1–4 minutes	Color etching Colors carbides and gamma prime in heat resisting steels
Delta Ferrite Etchant	Ammonium bifluoride: 20 g Potassium metabisulfite: 0.5 g Distilled water: 100 ml	Immersion at room temperature 1–2 minutes	Austenitic stainless steel and welds Reveals delta ferrite in welds
V2A Etchant	Hydrochloric acid: 119 ml Nitric acid: 12 ml Distilled water: 119 ml	Immersion or swabbing 20°C	Austenitic stainless steels
Weck’s No. 2 Reagent	Potassium permanganate: 25 g Sodium hydroxide: 25 g Distilled water: 250 ml	Immersion or swabbing 20°C	Stainless steels and nickel-based alloys Reveals grain boundaries, phases
Glyceregia	Glycerol: 10 ml Hydrochloric acid: 10 ml Nitric acid: 5 ml	Swab fresh solution only; do not store 5–60 seconds Rinse in water Dry with alcohol	General-purpose etch for 300-series austenitic stainless Reveals grain boundaries and twins; less aggressive than Adler's WARNING: mix fresh; aged glyceregia can decompose with gas evolution
10% Oxalic Acid (electrolytic)	Oxalic acid: 10 g Distilled water: 100 ml	Electrolytic at 6 V DC, stainless cathode 15–60 seconds Rinse in water; dry with alcohol	Austenitic stainless steels: reveals grain boundaries and sensitization Standard practice per ASTM A262 Practice A for intergranular attack screening
Marble’s Reagent	Copper sulfate (CuSO₄): 10 g Hydrochloric acid: 50 ml Distilled water: 50 ml	Swab or immerse 5–60 seconds Rinse in water; dry with alcohol	400-series martensitic and ferritic stainless steels Also used as a modified version for PH/maraging grades Reveals matrix and carbide distribution
Fry’s Reagent	Cupric chloride (CuCl₂): 12.5 g Hydrochloric acid: 100 ml Distilled water: 75 ml Ethanol: 65 ml	Immerse or swab; seconds to minutes Rinse in water; dry with alcohol	Martensitic and precipitation-hardening stainless steels Maraging steels respond well to a modified version Reveals martensitic structure and aged microstructure

Troubleshooting

Common etching issues and how to resolve them.

Over-etching

Reduce time by 30–50% and monitor. For sensitive grades like 316L, use shorter etching times.

Under-etching

Increase time by 10–20 seconds or ensure etchant is fresh. For duplex grades, consider stronger etchants.

Uneven Etching

Ensure sample is dry with consistent immersion motion. For large samples, consider electrolytic etching.

Staining

Rinse immediately and dry with compressed air. For martensitic grades, use ethanol rinse to prevent rust.

Sigma Phase Detection

Use Murakami’s reagent at 60°C for 10–15 seconds to clearly distinguish sigma from other phases.

Heat-Affected Zones

For welded samples, combine etchants to reveal both base metal and HAZ microstructures.