304LN stainless round steel (ASTM A276; GB 022Cr19Ni10N) has a composition of 18.0–20.0% chromium (Cr), 8.0–12.0% nickel (Ni), 0.02–0.05% nitrogen (N), ≤0.03% carbon (C), ≤1.00% silicon (Si), ≤2.00% manganese (Mn), ≤0.045% P, ≤0.030% S.
Compared to 304N (0.05–0.10% N), 304LN's lower nitrogen content (0.02–0.05%) balances strength and ductility via controlled solid-solution strengthening:
Strength retention without ductility loss: Nitrogen enhances strength via solid-solution strengthening (lattice distortions), but high N (0.05–0.10% in 304N) can reduce ductility by increasing lattice strain. 304LN's lower N provides sufficient strengthening (tensile strength: 550–700 MPa, vs. 304's 485–655 MPa) while preserving ductility (elongation ≥40%, identical to 304).
Reduced nitride formation risk: High N in 304N can form chromium nitrides (CrN) at grain boundaries during welding, which depletes chromium and reduces corrosion resistance. 304LN's lower N minimizes CrN formation, ensuring the passive Cr₂O₃ layer remains intact-critical for steels in welded service.
Low carbon (≤0.03%) eliminates intergranular corrosion risk, while nickel stabilizes the austenitic microstructure-304LN's lower N ensures these traits are not compromised by excessive strength.