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.