Metal finishing Q&As since 1989

Does 17-4 PH turn grey during passivation?

When a machined surface of 17-4PH steel is passivated does the surface color change to dull grey?

Thanks,

A grey surface on 17-4 PH after passivation is usually an indication that there has been a heat treating problem. Specifically, the surface becomes enriched in nitrogen and therefore reverts to austenite or remains austenitic upon cooling to ambient temperature. This austenitic surface layer is then attacked by the acid bath more so than the martensitic layer would be. Discuss the possibility of surface contamination or furnace atmosphere problem with your heat treater.

Passivation of 17-4PH can many times be a problem with nitric acid, but we have been very successful with our citric acid based products. We can refer you to customers for details, but you should not ever have the problems of the surface turning dull grey. As stated above, if the heat treating has been done wrong you can get problems.

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