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I selected this excerpt on 316 SS:
Corrosion Resistance
Excellent in a range of atmospheric environments and many corrosive media - generally more resistant than 304. Subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 60°C. Considered resistant to potable water with up to about 1000mg/L chlorides at ambient temperatures, reducing to about 500mg/L at 60°C.
316 is usually regarded as the standard "marine grade stainless steel", but it is not resistant to warm sea water. In many marine environments 316 does exhibit surface corrosion, usually visible as brown staining. This is particularly associated with crevices and rough surface finish.
And this chart on 304:
Table 5. Possible alternative grades to 304 grade stainless steel
Grade
Why it might be chosen instead of 304
301L
A higher work hardening rate grade is required for certain roll formed or stretch formed components.
302HQ
Lower work hardening rate is needed for cold forging of screws, bolts and rivets.
303
Higher machinability needed, and the lower corrosion resistance, formability and weldability are acceptable.
316
Higher resistance to pitting and crevice corrosion is required, in chloride environments
321
Better resistance to temperatures of around 600-900°C is needed.321 has higher hot strength.
3CR12
A lower cost is required, and the reduced corrosion resistance and resulting discolouration are acceptable.
430
A lower cost is required, and the reduced corrosion resistance and fabrication characteristics are acceptable.
Hope this helps.
Chuck Wells
#475 Apollo
1110153994.0