Metallographic Stainless Steel Etchants
Etching stainless steels can be somewhat difficult due to the anti-corrosive nature of stainless steel. Austenitic or 300 series stainless steels typically have higher chrome as well as a significant amount of nickel (e.g. 304 stainless steel - 18% chrome, 8% nickel) which makes them harder to etch. Martensitic or 400 series stainless steels are easier to machine, however, they are not as corrosion resistant so they are easier to etch.
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:
Stainless steels must be properly prepared to reveal the true metallographic microstructure. A number of recommended procedures can be found at the following links:
Recommended Etchants
| Etchant | Conc. | Conditions | Comments |
|---|---|---|---|
| Adlers Etchant Ferric chloride Copper ammonium chloride Hydrochloric acid Distilled water |
45 gm 9 gm 150 ml 75 ml |
Immerse for several seconds. | A very effective etchant for 300 series, austenitic, duplex stainless steels |
| Carpenter Etchant Ferric chloride Cupric chloride Alcohol Hydrochloric acid Nitric acid |
8.5 gm 2.4 gm 122 ml 122 ml 6 ml |
Immerse for several seconds. | A nice etchant for 300 series, austenitic, duplex stainless steels |
| Kalling' No. 2 Cupric chloride Hydrochloric acid Alcohol |
12 gm 20 ml 225 ml |
Immerse or swab - seconds to minutes | For 400 series or martensitic stainless steel |
|
Modified Murakami's K3Fe(CN)6 Potassium hydroxide Distilled water |
30 gm 30 gm 150 ml |
1 second to several minutes by immersion or swabbing |
Mix potassium hydroxide into water before adding K3Fe(CN)6 |
|
Hydrochloric acid Selenic acid Ethyl alcohol |
20-30 ml 1-3 ml 100 ml |
Immerse at room temperature for 1-4 minutes | Color etching. Colors carbides and gamma prime phase in heat resisting steels |
|
Ammonium bifluoride Potassium metabisulfite Distilled water |
20 gm 0.5 gm 100 ml |
Immersion at room temperature for 1-2 minutes | Color etching. Etching of austenitic stainless steel and welds. Reveals delta ferrite in welds |
|
V2A Etchant Hydrochloric acid Nitric acid Distilled water |
119 ml 12 ml 119 ml |
Immersion or swabbing etch at 20 degrees Celsius |
For etching austentic stainless steels |
|
Wecks No. 2 Reagent Potassium Permanganate Sodium Hydroxide Distilled water |
25 gram 25 grams 250 ml |
Immersion or swabbing etch at 20 degrees Celsius |
Often used for stainless steels, nickel-based alloys, and sometimes other metals to reveal grain boundaries, phases, and other microstructural features |
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| 431 Stainless Steel, etched with Modified Murakami's, Mag. 400X (DIC) |
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