304 stainless round steel (ASTM A276; GB 06Cr19Ni10) contains 18.0–20.0% chromium (Cr), 8.0–10.5% nickel (Ni), ≤0.08% carbon (C), ≤1.00% silicon (Si), ≤2.00% manganese (Mn), ≤0.045% phosphorus (P), and ≤0.030% sulfur (S).
316 stainless round steel (ASTM A276; GB 06Cr17Ni12Mo2) shares most elements with 304 but has two key differences: it reduces chromium to 16.0–18.0% and adds 2.0–3.0% molybdenum (Mo), while increasing nickel to 10.0–14.0%.
These changes alter chemical behavior significantly: molybdenum in 316 forms a stable molybdate layer that enhances resistance to chloride-induced pitting corrosion-a critical chemical trait absent in 304. The higher nickel content in 316 stabilizes the austenitic microstructure more effectively than 304, reducing the risk of martensitic transformation (which can weaken the steel) in harsh chemical environments. Both grades use chromium to form a passive Cr₂O₃ oxide layer, but 304's higher chromium content gives it slightly better general oxidation resistance in non-chloride settings.