303 vs 304 Stainless 3

[jvanbeek]

How does type 303 stainless match up with type 304 stainless when considering corrosion properties? Would 303 be suitable for use in the food processing industry? (eg. equipment in meat packing plants)

 

[mcguire]

303 and 304 share the same basic chemistry except that 303 has added sulfur for machinabilty; the sulfides are solid state lubricants and chip breakers.
Any sulfide exposed to the surface is a corrosion pit starter. So items made from 303 have poorer corrosion resistance, even if you specify having the optional 0.6% Moly addition. The media in which this corrosion occurs will experience a pick-up in iron ions as a result of the pitting. There is no prohibition against the use of this grade in direct food contact, however. NSF only stipulates a minimum of 16%Cr in the alloys.
If you want to use 303 but avoid the corrosion, take the final machined part and passivate thoroughly. You can find this procedure at the FAQ's of stainlesscenter.com.