ASTM E407 No. 157
ASTM No. 157
Material Specific
Composition
Hydrogen chloride 40–70%, Chromium trioxide 10–25%
PACE product, by weight
Method
Immersion
Time
5–30 s
Alternative Names
Tags
Reveals
Grain boundaries, carbides, sigma phase in chromium-bearing stainless and nickel-base superalloys
Typical Results
HCl + chromic acid immersion etchant for stainless steels, Inconel, Hastelloy, and other Ni-base superalloys (matches ASTM E407 #157 family). Aggressive attack reveals grain structure and primary carbide network even in aged superalloys. CARCINOGENIC (Cr(VI)): full PPE and fume hood mandatory.
Application Method
Method:Immersion
Typical Time:5–30 s
Preparation Notes
PACE ASTM No. 157 is supplied ready-to-use. Composition (by weight):
| Ingredient | CAS No. | % | Hazardous |
|---|---|---|---|
| Hydrogen chloride | 7647-01-0 | 40–70% | Yes |
| Chromium trioxide | 1333-82-0 | 10–25% | Yes |
| Water | 7732-18-5 | 25–50% | No |
Application Notes
Immerse polished surface 5–30 s at room temperature. Rinse copiously with water, then ethanol.
Troubleshooting
Cr(VI) is a known human carcinogen; full containment required. Dispose as regulated waste. Solution darkens with use but remains active.
Storage Notes
Glass bottle with tight cap; secondary containment. Hazardous-waste disposal protocol. Stable many months.
Alternative Etchants
- Glyceregia
- Marble's Reagent
- 10% Oxalic Acid (Electrolytic)
- Inconel Etchant
Similar Etchants
- Chromic Acid (Electrolytic)