SUS316L vs SUS316LN: The Role of Nitrogen in Low-Carbon 316

Two Low-Carbon Variants of 316

SUS316L and SUS316LN are both low-carbon austenitic stainless steels defined in Japanese JIS standards such as JIS G4303. The suffix L indicates low carbon, limited to 0.03 percent maximum, which reduces the risk of intergranular corrosion after welding. SUS316LN is an enhanced version that adds nitrogen, typically 0.10 to 0.16 percent, to retain excellent corrosion resistance while offering higher mechanical strength.

Chemical Composition

Both grades share chromium 16.0 to 18.0 percent, nickel 10.0 to 14.0 percent, and molybdenum 2.0 to 3.0 percent, with carbon 0.03 percent maximum. The key difference is nitrogen: SUS316L allows up to 0.10 percent, typically below 0.03 percent, while SUS316LN specifies 0.10 to 0.16 percent.

Mechanical Properties

In the annealed condition SUS316L has a minimum yield strength of 205 MPa and tensile strength of 480 MPa, while SUS316LN has a minimum yield strength of 245 MPa and tensile strength of 520 MPa, about 20 percent higher yield strength from nitrogen solid-solution strengthening. Elongation is 40 percent for 316L and 35 percent for 316LN, with hardness up to 217 and 220 HB respectively.

Corrosion Resistance

Both ultra-low-carbon grades show excellent resistance to intergranular corrosion, and no post-weld heat treatment is required. SUS316LN performs slightly better in pitting and crevice corrosion because nitrogen enhances passive film stability in chloride environments such as seawater or brine. Because of its higher strength, stress control is more critical for 316LN in corrosive environments to avoid stress corrosion cracking.

Welding and Fabrication

Both grades weld well, but SUS316LN work-hardens faster because of nitrogen, so tool wear and forming forces should be considered. For welding, SUS316L uses ER316L filler, while SUS316LN should use nitrogen-bearing filler such as ER316LN to retain weld zone strength; using ER316L may reduce weld strength.

Selection Guidance

Choose SUS316L for corrosion-focused, weld-friendly applications at moderate strength. Choose SUS316LN where both high strength and corrosion resistance are required in pressure or structural applications, such as cryogenic vessels, heat exchangers, and high-pressure piping.

Frequently Asked Questions

Q: What does the LN in SUS316LN mean?

A: Low carbon plus nitrogen, typically 0.10 to 0.16 percent.

Q: How much stronger is SUS316LN?

A: About 20 percent higher yield strength than SUS316L.

Q: Do both grades resist intergranular corrosion?

A: Yes, with carbon limited to 0.03 percent.

Q: What filler is used for SUS316LN?

A: Nitrogen-bearing filler such as ER316LN.

Q: What applications use SUS316LN?

A: Cryogenic vessels, heat exchangers, and high-pressure piping.

Q: Which grade is easier to form?

A: SUS316L, because 316LN work-hardens faster.

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