Black Oxide a 300-series stainless? 1

[swertel]

I just saw this on a drawing and admittedly have never seen it before and don't understand why they would bother with the expense of the extra process, short of pretty color.

Material: 302 or 304 Stainless
Finish: Passivate per QQ-P-35, Type VI or VII. Black Oxide per MIL-C-13924, Class 4.

It may just be my experience with stainless steels, but I have only ever used Black Oxide on plain carbon steels and tool steels, not stainless. And why do I need the extra corrosion inhibiting oxide layer of the black oxide process after I have passivated it? Doesn't that defeat the purpose of the passivate?

--Scott

http://wertel.eng.pro

 

[CoryPad]

The only reason to create the black layer is for appearance or optical/thermal properties, not for corrosion resistance.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[swall]

We have done it on 17-7 stainless springs used in a military application.Other than that, it makes no sense.

 

[swertel]

CoryPad guessed it. Why it didn't occur to me until I read his statement regarding "optical properties" I don't know.

The component is on an exposed part of the product that can not be shiny or reflective. Black Oxide allows for functionality of the part, where painting would not, and gets rid of the reflectivity of that particular component.

--Scott

http://wertel.eng.pro