308 has less nickel and more chromium than 316. Different corrosion resistance. An excerpt from
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When to use a 308L, 309L or 316L filler metal
308L and 308LSi is predominately used on austenitic stainless steels, such as types 301, 302, 304, 305 and cast alloys CF-8 and CF-3.
For high temperature applications such as in the electrical power industry, higher carbon 308H electrodes will provide superior creep resistance than does 308L .
Use 309L and 309LSi when joining 309 or mild steels / low alloy steels to stainless steels. Use 309 when joining dissimilar stainless steels such as 409 to itself or to 304L stainless. CG-12 is the cast equivalent of 309.
Some 308L applications may be substituted with 309L filler metal, but 316L or 316 applications generally require molybdenum. Note, 309L contains no molybdenum.
316L and 316LSi should be used with 316L and 316 base metals. CF-8M and CF-3M are the cast equivalents of 316 and 316L, respectively.
Type 347 stainless steel filler metal is used for 347 and 321 base materials because it matches these stabilized grades.
CF-8C is the cast equivalent of 347. Type 347 filler metal is also suitable most 308L filler metal applications.