BLACK POWDER ON 440C AFTER PASSIVATION. 1

[TREE342]

HI, EVERYBODY,
I RUN INTO A PROBLEM HOPING SOMEONE CAN HELP ME DETERMINE WHAT MIGHT BE THE CAUSE OF THAT.
I JUST RECEIVED PARTS BACK FROM PASSIVATION WHICH HAVE LOOSE PITCH BLACK POWDER ALL OVER THE PARTS. THE POWDER CAN BE SMEARED OFF EASILY.
MATERIAL IS 440C, ROUGH MACHINED PRIOR TO HEAT TREATED TO Rc54~56, SEVERAL GRINDING OPERATIONS AFTER THAT. THEN GET MAGNETIC INSPECTED AND PASSIVATED.
THANK YOU ALL IN ADVANCE.

 

[EdStainless]

Are the parts demagetized? real well? It might be fines from grinding that are clinging to the surface.
Or, it could be a result of a more agressive passivation resulting in a iron oxide smutt.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[mcguire]

One can get a powder like that from pickling; a carbide reside left as the metal matrix is dissolved. 440C has lots of carbides and lots of metal loss during pickling.
Is your processor using too strong an acid treatment, such as one appropriate for 304?

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[TREE342]

HI, EDSTAINLESS & MCQUIRE,

THANK BOTH OF YOU FOR YOUR TIMELY FEEDBACK. DUE TO SEVERE DIMENSIONAL DAMAGE, .001 LOSS PER SURFACE, WE HAVE TO SCRAP OUT ENTIRE LOT. PROCESSING VENDOR ADMITTED IS THEIR MISTAKE HOWEVER HASITATE TO DISCLOSE THE DETAILS. THANKS AGAIN.