Generally, the best method for nickel alloy is just mechanical cleaning followed by flashing pickling. However, steel & brass brush must be avoided as small particles of steel & brass can discolor nickel alloy or induce rust.
I believe your case is exactly same as the one described in ASM Metal handbook Volume 5.(Surface Engineering of Nickel and Nickel Alloys )
(Quoted from ASM Metal handbook Vol 5 Surface Engineering of Nickel and Nickel Alloys )
Detection and Removal of Embedded Iron.
During mechanical operations such as rolling to shape or hot pressing, small particles of iron may become so firmly embedded in the surfaces of nickel alloys that they cannot be removed by the cleaning methods normally used for dissolving grease or cutting compounds. Under certain corrosive conditions, such iron particles can initiate local attack.
(Omitted)
A solution of hydrochloric acid and ferric chloride, Formula 12, is used to remove embedded iron. This solution should be used cold and should remain in contact with the metal for only the minimum time required for iron removal, not exceeding 1 h. After the work is removed from the solution, it should be rinsed thoroughly in cold water, then rinsed again in warm water. The detection tests should be repeated to verify the removal of the iron.
Formula 12
HCL 1.16 Sp gr - 1 wt%, 30 ml, ambient temperature
FeCl3 - 1 wt % - 11g, ambient temperature
Water - 1000 ml, ambient temperature
P.S. Next time, do not use steel brush but si carbide or al oxide.
SiHyoung Lee
