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Blackodizing a Nitrided washer for identification purpose

Sir,
We have TWO Spherical Washers, which looks alike but with a slight dimensional variation.These washers are liquid Nitrided to achieve a surface hardness of about 600 HV min. It becomes little difficult to identify the right spherical washer during assembly operation.
Sir, can the process of Blackodizing (or Black Oxide coating) be used over Nitrided layer on one of these washers (for identification purpose) without compromising the hardness already achieved by Nitriding process (I gather, Hot Black Oxide coating process requires a temp. of about 300 °F which could drop down the required hardness achieved through Nitriding). OR can Nitriding itself impart a different color shade by the addition of some chemical during the process itself, so that identification of these two types of washers become easy for assembly personnel.
Your expertise is awaited.
Regards,

Krishnadas Nair
Automobile manufacturing - Mumbai, Maharashtra, India
2007

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2007

Gentleman,

You can adopt the process of Tufftriding which uses salt bath dip process of Nitriding and imparts Black color on quenching.
Process consists of Preheating, Nitriding in Cyanide salt and quenching in quenching salt then rinsing in water and drying.

SHANKARANARAYANAN N
- Bengalooru, Karnataka, India