Corrosion of Stainless Steels

[slv122]

i need to know, what is the most corrosive resistent stainless steel. we are debating between 316 and 304. 316 is subject to more pitting and crevice corrosion. also what is the best method of testing them. we need to determine about how long they will go without corroding.
as to what we plan to use this for, it is used to hold gears in a water motor that run a lawn sprinkler. it will be in a water motor that will be submerged in water (all types) for lenghts of time. i read that the sea water (fog) test is the best method. i also need to know if this test is best and how long should you run this test for.

 

[mcguire]

I gave an answer to this in the other forum where it was asked, but I do need to state very clearly that 316 is clearly superior to 304 in both pitting resistance and crevice corrosion resistance.
The FAQ's in this forum tell how pitting resistance is proportional to chemistry. Resistance to crevice corrosion obeys the same formula.

 

[mcguire]

slv122....sorry, that FAQ is in the corrosion engineering forum.

 

[roberth]

304 is softer, and would probably have less corrosion resistance. What about 440 stainless?

Robert Hall

 

[mcguire]

440 doesn't measure up to 304 in corrosion resistance because it lower chrome, some chrome tied up by carbon, no nitrogen in solution and just a small amount of moly. But if you're using it for fresh water it may be just fine.
It can be hardened like carbon or alloy steel.