SS304 is equal to casting grade CF8; SS316 is casting grade CF8M.
CF8 and CF8M is defined in ASTM A743 or ASTM A351 standard. 304 or 316 is the popular name in steel plate and pipe usage.
Those two popular stainless steel can be made by sand casting or lost wax precision investment casting, and they are popular used in most industry.
For the detailed chemistry and mechanical property CF8/CF8M, pls visit:
Stainless Steel Impellers