316L steel (1.4404): properties, composition, equivalents
316L (1.4404, UNS S31603) is 316 with carbon capped at 0.030 %: the same molybdenum-bearing alloy, specified so welds do not sensitise.
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What is 316L?
316L is 316 with the carbon taken out, and that is the whole specification: 0.030 % maximum against 0.08 %. Chromium, nickel and molybdenum are unchanged, so the corrosion resistance of the base metal is unchanged too.
The carbon matters in one place — beside a weld. Held between roughly 425 and 815 °C, chromium and carbon combine at the grain boundaries; the chromium locked into those carbides is no longer available to protect the steel, and a narrow band parallel to the weld corrodes while the weld itself and the plate beyond it stay sound. That is sensitisation, and less carbon means less of it. It is why 316L is the default for welded fabrication and why 316 is not.
The 2 to 2.5 % molybdenum is what separates the 316 family from 304 and is the reason anyone pays for it: molybdenum resists pitting by chlorides, which is the failure mode in seawater, de-icing salt, swimming pools, brine and most food processing.
One practical note that settles most enquiries: the great majority of material on the market is dual certified 316/316L — carbon below 0.030 % while still meeting the higher 316 mechanical minima — so a single certificate satisfies both specifications.
316L chemical composition
| Element | Mass % | Note |
|---|---|---|
| C | ≤ 0.03 | the definition of the grade; 316 allows 0.08 % |
| Cr | 16.5 – 18.5 | |
| Ni | 10 – 13 | |
| Mo | 2 – 2.5 | the pitting resistance that separates 316 from 304 |
| Mn | ≤ 2 | |
| Si | ≤ 1 | |
| P | ≤ 0.045 | |
| S | ≤ 0.015 | |
| N | ≤ 0.11 |
EN 10088-2 for 1.4404; the ASTM A240 ranges for S31603 are close but not identical (Ni 10.0–14.0, N ≤ 0.10). PREN, calculated as Cr + 3.3 Mo + 16 N, lands at roughly 24–25 — comfortably above 304's 18–19 and well below a duplex or super-austenitic grade.
316L mechanical properties
| Thickness / condition | Yield strength ReH / Rp0.2 MPa (ksi) | Tensile strength Rm MPa (ksi) | Elongation A % | Hardness |
|---|---|---|---|---|
| sheet/plate, annealed (ASTM A240) | ≥ 170 (≥ 24.7) | ≥ 485 (≥ 70.3) | 40 | ≤ 217 HB / ≤ 95 HRB |
| cold-rolled sheet, annealed (EN 10088-2) | ≥ 240 (≥ 34.8) | 530–680 (76.9–98.6) | 40 | — |
| hot-rolled plate, annealed (EN 10088-2) | ≥ 220 (≥ 31.9) | 520–670 (75.4–97.2) | 45 | — |
| bar, annealed (A276) | ≥ 170 (≥ 24.7) | ≥ 485 (≥ 70.3) | 40 | — |
| TP316L pipe (A312) | ≥ 170 (≥ 24.7) | ≥ 485 (≥ 70.3) | 35 | — |
| 316 for comparison (A240) | ≥ 205 (≥ 29.7) | ≥ 515 (≥ 74.7) | 40 | — |
The ASTM and EN minima differ and both are correct: ASTM A240 sets a 170 MPa floor for S31603 while EN 10088-2 sets 240 MPa for cold-rolled 1.4404 sheet. A design that quotes '316L yield strength' without naming the standard and the product form is quoting an incomplete number.
Impact toughness
316L requires a minimum Charpy V-notch energy of J at -196 °C (austenitic — no ductile-to-brittle transition). Austenitic stainless steels have no transition temperature and stay tough to cryogenic conditions, which is why 316L is used down to −196 °C in LNG and laboratory service. Impact testing is specified by the application code rather than by the material standard.
316L equivalent grades
| Grade | System | Match | Why / differences |
|---|---|---|---|
| 1-4404 | EN (European) | Identical | 1.4404 is the EN material number for this grade; X2CrNiMo17-12-2 is its descriptive name. |
| 1.4404 | EN (European) | Identical | UNS S31603 (ASTM A240): C ≤ 0.03, Cr 16–18, Ni 10–14, Mo 2–3; 1.4404 sits inside the 316L window and is dual-certified. |
| 316 | AISI / SAE | Near | Identical alloy with carbon to 0.08 % and slightly higher strength minima. Most material sold today is dual certified to both. |
| 1.4571 | EN (European) | Near | Same corrosion class; 316L achieves weld-zone stability by low carbon instead of Ti. Usual substitute outside Europe. |
| 304 | AISI / SAE | Functional | The same austenitic family without molybdenum. Adequate in most atmospheres, not in chlorides — the substitution runs one way only. |
| 304L | AISI / SAE | Functional | UNS S31603 adds 2–2.5 % molybdenum for chloride resistance. Specify it instead of 304L near the sea, in de-icing salt or in pool environments — the low-carbon logic is identical. |
| 2205 | EN (European) | Functional | Duplex with roughly twice the yield and a PREN around 35. Specified when 316L pits or when wall thickness has to come down. |
Identical = same composition and mechanical limits within rounding. Near = one limit differs (e.g. carbon max or impact temperature). Functional = interchangeable for most uses after an engineering check. Full cross-reference for 316L →
Old and superseded designations
| Old name | Standard | Note |
|---|---|---|
| X2CrNiMo17-12-2 | EN 10088-2 name | The descriptive EN designation: 0.02 % C, 17 % Cr, 12 % Ni, 2 % Mo. |
| SUS 316L | JIS G4304 / G4305 | The Japanese designation; ranges are effectively the same. |
| 1.4435 | EN 10088-2 | Not the same grade — a higher-molybdenum, higher-nickel variant (2.5–3.0 % Mo) often specified for pharmaceutical service and sometimes confused with 1.4404. |
Product forms and tolerance standards
Product forms: sheet, plate and coil (ASTM A240 / EN 10088-2), bar and section (A276 / EN 10088-3), welded and seamless pipe (A312 TP316L), tube for instrumentation and hygienic service (A269, A270), fittings, flanges and A4-class fasteners.
Dimensional tolerances: sheet and plate: ASTM A480 / EN ISO 9445; bar: ASTM A484 / EN 10278; pipe: ASTM A999 general requirements; surface finishes: 2B, BA, No. 4, No. 8 to ASTM A480 Table A1.1.
Key property values
316L chemical composition
C ≤ 0.030 %, Cr 16.5–18.5 %, Ni 10.0–13.0 %, Mo 2.0–2.5 %, Mn ≤ 2.0 %, Si ≤ 1.0 %, N ≤ 0.11 % (EN 10088-2 for 1.4404). ASTM A240 allows nickel to 14.0 %. The molybdenum is the working element; the carbon ceiling is the name.
316L yield and tensile strength
ASTM A240 requires 170 MPa yield and 485 MPa tensile minimum; EN 10088-2 requires 240 MPa yield and 530–680 MPa tensile for cold-rolled sheet. Real annealed material usually runs well above both. The grade work-hardens steeply, so a cold-worked section tests far harder than an annealed one.
316L corrosion resistance
PREN ≈ 24–25, against 18–19 for 304. That buys real chloride tolerance — coastal atmosphere, food brines, chlorinated water at moderate temperature — but not immunity. In warm seawater, in concentrated brine or under deposits, 316L pits, and the step up is duplex 2205 or a 6 % molybdenum super-austenitic grade.
316L vs 316
Same alloy, carbon 0.030 % against 0.08 %, and ASTM minima 35 MPa lower on yield. Use 316L for anything welded and not solution annealed afterwards; use 316 for sustained service above about 500 °C, where the higher carbon carries better creep strength, or 316H where a code allows it.
316L in fasteners: A4
The A4 property class in ISO 3506 is the 316/316L family, most commonly A4-70 for bolts. A4 is specified for marine and chloride service where A2 (the 304 class) corrodes; the number after the dash is the strength class, set by cold work, not by the alloy.
Weldability
316L is the reason the L grades exist and it welds by every standard process — TIG, MIG, MMA, plasma and laser — without preheat and without post-weld heat treatment at normal thicknesses. Use 316L filler (ER316L / E316L-16), or 309L for a dissimilar joint to carbon steel. Heat input should be kept moderate and interpass temperature controlled, not because of sensitisation but because austenitic steel distorts: its thermal expansion is around 60 % greater than carbon steel's while its conductivity is a third. Back-purge with argon on pipe to prevent oxide on the root, and pickle or passivate afterwards — heat tint is chromium-depleted and corrodes, which is the single most common cause of 'the stainless rusted' on a new installation.
Machining, forming and heat treatment
Machinability is poor by carbon-steel standards, roughly 35–45 % of a free-cutting reference, and the reasons are gumminess and work hardening rather than hardness. Use sharp tooling, positive rake, rigid setups, generous coolant and — critically — a feed heavy enough to cut under the work-hardened layer rather than rubbing on it. Cold forming is excellent: 40 % elongation and steep work hardening make it a deep-drawing material, at the cost of high press loads and springback. Interstage annealing is normal on severe draws.
Typical applications
- Welded process pipework and vessels in food, dairy, brewing and pharmaceutical plant
- Marine and coastal fittings, balustrade, fasteners (A4) and architectural components
- Heat exchangers and tanks handling chloride-bearing water
- Chemical and pulp plant where 304 pits and duplex is not justified
- Hygienic tube and fittings with orbital-welded joints
- Cryogenic service down to −196 °C, where austenitic toughness is the requirement
316L compared with related grades
Frequently asked questions
What does the L in 316L mean?
Low carbon: a maximum of 0.030 % against 0.08 % for 316. Chromium, nickel and molybdenum are unchanged, so the L affects welding behaviour rather than the corrosion resistance of the base metal.
Is 316L better than 316?
For welded fabrication, yes — it will not sensitise in the heat-affected zone. For sustained service above about 500 °C, no: the lower carbon means lower creep strength, and 316 or 316H is the correct choice there.
What is the difference between 316L and 304?
Molybdenum. 316L carries 2.0–2.5 % of it and 304 has none, which lifts the pitting resistance number from about 18–19 to about 24–25. In dry or mildly wet service they behave alike; in chlorides — sea air, brine, pool water, de-icing salt — 304 pits and 316L does not.
What is the yield strength of 316L?
It depends on which standard and which product form. ASTM A240 sets a minimum of 170 MPa for annealed sheet and plate; EN 10088-2 sets 240 MPa for cold-rolled sheet of the same grade. Both are correct, so the standard has to be named alongside the number.
Is 316L magnetic?
Not in the annealed condition — it is austenitic, with a relative permeability close to 1.0. Heavy cold work such as deep drawing or severe bending induces some martensite and a part can then register weakly magnetic, which is normal and not a sign of the wrong grade.
What is dual certified 316/316L?
Material whose carbon is below 0.030 %, satisfying 316L, while its mechanical properties still meet the higher 316 minima. One certificate then covers both specifications, which is how most 316 is supplied today.
Can 316L be used in seawater?
In moving, aerated seawater at ambient temperature it performs for a time; in warm, stagnant or deposit-covered seawater it pits and crevice-corrodes. For sustained seawater duty the specification steps up to duplex 2205, super duplex or a 6 % molybdenum austenitic grade.
Related grades
Verified against EN 10088-2:2014 · ASTM A240/A240M; EN 10088-2:2014 (1.4404 composition and mechanical properties); ASTM A240/A240M (UNS S31603). Last checked: November 2026.