This standard covers nitric acid and nitric acid / sodium dichromate solutions. Specific treatments are however also specified. The standard also allows any combination of citric acid concentration, temperature and time, provided that the passivation test criteria can be met. Practice E – Potassium Ferricyanide-Nitric Acid Test ASTM A967 citric acid passivation treatments: The standard notes that the high carbon martensitic stainless steels, such as 440C, are not suitable for acid passivation as they can be attacked or be subject to hydrogen embrittlement. Unlike ASTM A380, the standard does not require specific solutions for particular stainless steel grades or types, although 3 specific treatments are identified. Parts treated however must pass specific tests to confirm the effectiveness of the passivation, although in practice the tests are for the detection of the effects of residual iron contamination on the surface of the parts. In addition, this standard also includes citric acid treatments. The nitric acid treatments are similar to those identified in ASTM A380. This standard covers both nitric and citric acid treatments.
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