Summary for white dusting on stainless Discussion
White dusting on nitric acid passivated 304L parts is discussed as a possible cleaning or surface-prep issue rather than a definite material defect. Jon Danielson says some parts treated in ASTM A967 Nitric 2 and precleaned with Chemetall Oakite Aluminum Cleaner 166 dry with a light white coating that can be wiped off or removed with Scotch-Brite, while others do not show it. His finisher suggested slightly porous material, but Willie Alexander notes that if the material were the cause, he would expect all parts to look the same. Willie says an aluminum soap cleaner may or may not be sufficient depending on soil level and recommends trying ultrasonic cleaning before passivation as a first step, or testing another supplier. The thread does not identify the white film as a specific defect, but it points toward inadequate cleaning or process variation as the more likely explanation.
Q. I have some 304L stainless parts treated in ASTM A967 Nitric 2 bath. The parts are precleaned in a Chemetall Oakite Aluminum Cleaner 166. When the parts are done and dry, a light white coating is left on some of the parts. I would like to stress that not all parts have this light coating. It almost looks like dust that you could wipe off. It is something you could take off with a scotch brite pad. My metal finisher says this could be the result of a slightly porous material.
What could this be and is this something that I should be worried about?
Thanks a lot!
Jon
Jon Danielson
engineer – Loveland, Colorado
January 12, 2012
January 13, 2012
Jon
An aluminum soap may or may not be adequate for cleaning your parts, depending on how soiled they are.
I would try an ultrasonic cleaning prior to passivation as a first step. You could always try another supplier. If it is the material, I would expect all the parts to have the same appearance.
Willie Alexander
– Colorado Springs, Colorado