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Verifying Passivation of 15-5CRES

We are in the process of machining some 15-5CRES material tempered to a H-1025 condition. We would like to passivate the area to be ground down with a diamond grinding wheel but there is an adjacent surface that has a tungsten carbide friction coating that will be attacked by nitric acid. I don't know if this grinding wheel has been used on other parts or not. In order to determine whether any free iron is contained on the wheel from another machining operation can we perform a copper sulphate [on eBay or Amazon]test on the grinding wheel since we can't perform it on the 15-5CRES material (martensite condition-false positive condition)? Please let me know your thoughts.

You can probably get by with a copper sulphate test on the 15-5CRES. It may give you a positive reading, but if you get a negative reading you know that it is okay. If you get a positive reading you will not be certain, of course. You can also get by with passivation with a citric acid based formulation, with the right process, which will not be a problem.

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