304L has C ≤0.03% for better intergranular corrosion resistance after welding; 304 has slightly higher strength and lower cost. Prefer 304L for welded structures.
304 and 304L are the two austenitic grades most often confused. The difference is carbon content and application:
• 304: C ≤0.08%, slightly higher strength, slightly lower cost; common for general formed and non-critical welded parts.
• 304L: C ≤0.03%, lower risk of chromium depletion at grain boundaries after welding and better intergranular corrosion resistance; preferred for heavy sections or parts that cannot be solution annealed after welding.
Guidance:
1) Welded and no post-weld solution annealing → 304L.
2) Not welded, complex shape, cost sensitive → 304.
3) Long high-temperature service (>450°C): assess sensitisation risk and consider stabilised grades (321/347).
4) State "304L per ASTM A240" or "022Cr19Ni10 per GB/T 3280" to avoid 304 being passed off as 304L.
Note: 304L has a slightly lower minimum strength; if the design used 304 strength values, re-check when switching to 304L.
