Black coating for 1018 steel that will not scratch

A. I would suggest that you consider salt bath nitriding such as is offered by Kolene.

My understanding is that if the finish is not quite black enough for you, you can do a black oxide on top of it which, if it scratches, would only reveal the non contrasting dark gray color of the underlying nitriding. As I understand it, this is the approach used on handguns by one of the world's most respected makers.

A. I agree with Ted's suggestion of the Kolene ferritic nitrocarburizing process. It provides excellent wear and corrosion resistance, and the color is often quite dark, especially when processed through Kolene's QPQ process.

A. Hi Murali. The QPQ process is salt bath nitriding and does case hardening. Black oxide is a superthin black coloration and does not impart wear resistance.

I think Toby probably put it better than I did, that black coloring is part of the QPQ process rather than a post treatment after it. As you see, we appended your inquiry to an earlier thread which includes a link explaining the QPQ process. Good luck.

Regards,

Thanks for your reply Ted!!

My confusion arose from the fact that we are right now carrying out Salt bath nitrocarburising, then black oxidising and then polishing. The metal surface is starting to erode in service as if there is no hardened layer. And I am unable to point my finger where the process is going wrong, during nitrocarburising or black oxidising. We are carrying out lapping (polishing) at the end because we are unsure of the thermal distortion that may occur.

A. Hi Ahmed. QPQ is a reasonably attractive, surface hardening, corrosion-proofing process. Zinc phosphate is none of those three. If it doesn't actually have to be black, hard chrome plating might be best, and QPQ is often promoted as an alternative to hard chrome. If it's a cylinder rod, that might be your only reasonable alternative. But black chrome plating might be the closest alternative depending on how you look at it.

Other alternatives really depend on what the item is, and the service condition. Black oxide & oil is used on firearms but is nowhere near the equal of QPQ in wear resistance or corrosion resistance. Gas nitriding or plasma nitriding might function while not being aesthetic enough for you. Good luck!

Regards,