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Letter 31052
Corrosion resistance of 303 SS vs 304 SS
[Rhode Island]
++++
I notice an etching of a 303 Stainless steel when submersed in 38%
H2SO4 under vacuum. It seems to me 304 did not exhibit the same
problem. Is this correct?
Colin McClennan
electronics mfgr - Providence, Rhode Island, USA
++++
Could be, Colin. 303 is the free machining version of 304- meaning
it has controlled amounts of 'dirt', manganese sulfides, which cause
the machining chips to break easily. We, and others, have noticed
passivation problems with 303 that we don't see with 304. I have no
experience with your particular corrosive, but could easily believe
303 is inferior to 304.

Lee Gearhart
- East Aurora, NY
++++
I agree with Lee that 303 will usually be less corrosion resistant
than 304. You may find that soaking the 303 first in hot NaOH
solution or similar will help you immensely by removing the sulfides
from the surface before passivation.
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