What does the “L” mean in 304L or 316L?

The “L” in grades like 304L and 316L stands for low carbon. An L grade is the same alloy as its standard version, with a lower maximum carbon content — and, as a result, slightly lower minimum strength.

Chromium, nickel and molybdenum ranges are the same or nearly the same between each standard grade and its L grade — see the full chemistry tables in our 304L / 304 / 302 and 316 / 316L articles.

Why low carbon matters for welding

Exposure to 800–1500 °F (427–816 °C) can precipitate chromium carbides at grain boundaries (“sensitization”), leaving the steel open to intergranular attack in aggressive environments.

• 304L: Low-carbon Type 304L is preferred for parts placed in service as-welded. Its low carbon delays — but does not eliminate — carbide precipitation during long exposure in that range.
• 316L: 316 and 316L generally perform equally well. Where corrosion is severe enough to attack welds and heat-affected zones, 316L is preferred for welded parts because its low carbon improves resistance to intergranular corrosion.

For more detail, see the 302 / 304 / 304L / 305 and 316 / 316L tech sheets.

What it doesn’t change

An L grade is not less corrosion resistant than its standard grade. The main trade-off is the slightly lower minimum strength shown in the table above.

How this applies to our material

If your application calls for 304 or 316, 304L or 316L can usually be substituted. Our material makes that simple: it’s made to the L grade’s low carbon limit and tested to the standard grade’s higher strength minimums, so it’s certified to both.

• Our 316 / 316L is dual certified to 316 and 316L.
• Our annealed 304L is triple certified to 304L, 304 and 302.

This article is educational information only. Always order to the current revision of the governing specification.