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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.

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:

http://www.metallographic.com/Procedures/Stainless%20Steel%20Description.htm

http://www.metallographic.com/Brochures/Met-Manual-2b.pdf

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

 

 Etchant Conc. Conditions Comments
Adlers 300 Series
Stainless Steel Etchant
Ferric chloride
Copper ammonium chloride
Hydrochloric acid
Distilled water
45 grans
9 grams
150 ml
75 ml
Immerse for several seconds. A very effective etchant for 300 series, austenitic, duplex stainless steels
Carpenter 300 Series
Stainless Steel Etchant
Ferric chloride
Cupric chloride
Alcohol
Hydrochloric acid
Nitric acid
8.5 grans
2.4 grams
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 grams
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 grams
30 grams
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 grams
0.5 grams
100 ml
Immersion at room temperature for 1-2 minutes Color etching. Etching of austenitic stainless steel and welds. Reveals delta ferrite in welds.