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The copper sulfate test is intended to test the effectiveness of passivation. It can also be used to determine if there is a need for passivation.

The purpose of the copper sulfate test is to determine the presence of free iron which is usually induced onto the surface of a part during fabrication with steel components. (Note: parts without surface contaminant iron may pass the test prior to any passivation treatment.) The principle of the test is based on an oxidation-reduction reaction which causes the dissolved copper ions to deposit or plate out onto the free iron particles.

This test is recommended for the detection of free iron on the surface of austenitic stainless steels in the 200 and 300 series, precipitation hardened stainless steels, and ferritic 400 series stainless steels having a minimum of 16 % chromium. This test is not recommended for martensitic 400 series stainless steels with less than 16 % chromium because these steels will give a positive indication irrespective of the presence or absence of anodic surface contaminants. This test is also not recommended for parts with laser marks.

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