Letter 31052

Corrosion resistance of 303 SS vs 304 SS  

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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 metallurgist 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.

Lee Kremer Stellar Solutions, Inc. McHenry, Illinois

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