Guide
316 vs 316L stainless: which grade should the drawing call out?
316L stainless is the low-carbon version of 316, the molybdenum-bearing austenitic stainless steel; in the 316 vs 316L choice the two share the same chromium, nickel and molybdenum ranges, and the defining specification difference is how much carbon each one is allowed to carry, with slightly lower strength minimums for 316L as the trade-off. Call 316L for any part that will be welded, brazed or stress relieved; call 316 only when the design relies on its higher strength minimums; and in either case state whether dual-grade 316/316L bar, which meets both, is acceptable.
By Saola Manufacturing engineering team · Published · Updated
This guide is for design engineers and buyers who have to put a stainless grade on a drawing and then read the mill certificate that comes back. It covers what the carbon limit does, why welding is the deciding question, what dual-grade 316/316L bar is and when it satisfies a callout, the cases where neither plain grade is right, and the exact wording to use on the drawing and the RFQ. Only the public scopes of the ASTM documents are quoted; take limits from your own copy of the current edition before you release a drawing.
On this page
What is the real difference in 316 vs 316L?
Carbon is the difference: 316 allows more than two and a half times as much carbon as 316L, and in exchange it carries slightly higher minimum strength in the annealed condition. Chromium, nickel and molybdenum ranges are the same in the ASTM bar and plate specifications.
Per ASTM A276, the bar specification most machined parts are bought to, carbon is capped at 0.08% for 316 (UNS S31600) and at 0.030% for 316L (UNS S31603). The same two limits appear in ASTM A240 for plate, sheet and strip, so a welded assembly that mixes machined bar and cut plate can be specified consistently across both product forms.
Both grades get their advantage over 304 from molybdenum, which raises resistance to pitting and crevice corrosion in chloride environments. That benefit is identical in 316 and 316L, because the molybdenum range is identical. Lower carbon does not make 316L more resistant to general or pitting corrosion on a part that has never been heated; it only protects the steel from what heat can do to it, which the next section explains.
The price of lower carbon is a little strength. Carbon is an interstitial strengthener, so the annealed minimums for 316L are lower than for 316, as the table shows. For most machined parts the difference never governs the design, but it does matter for thin-walled pressure parts and for anything sized right at the allowable stress.
Outside the US the pair appears as 1.4401 and 1.4404 in EN 10088-3 and as SUS316 and SUS316L in JIS G4303. The names map closely, but the composition windows are not identical in every element, so a drawing that will be sourced in Asia should state which equivalents are acceptable rather than assume they are interchangeable.
| Property | 316 (UNS S31600) | 316L (UNS S31603) |
|---|---|---|
| Carbon, max | 0.08% | 0.030% |
| Chromium | 16.0–18.0% | 16.0–18.0% |
| Nickel | 10.0–14.0% | 10.0–14.0% |
| Molybdenum | 2.00–3.00% | 2.00–3.00% |
| Tensile strength, min (annealed bar) | 75 ksi (515 MPa) | 70 ksi (485 MPa) |
| Yield strength, min (annealed bar) | 30 ksi (205 MPa) | 25 ksi (170 MPa) |
| EN 10088-3 number | 1.4401 | 1.4404 |
| JIS G4303 designation | SUS316 | SUS316L |
| As-welded sensitization risk | Present, rises with heat input and section | Low under normal welding |
Why does carbon content matter after welding?
Heat from welding can pull carbon and chromium together into carbides along the grain boundaries, leaving chromium-depleted zones that corrode preferentially; that condition is called sensitization. Keeping carbon low starves the reaction, which is why 316L is the default for welded parts.
The British Stainless Steel Association describes the mechanism in its note on polythionic acid stress corrosion cracking: on exposure to roughly 450 to 900 °C, chromium carbides precipitate at grain boundaries. Carbon diffuses quickly; chromium diffuses slowly, so the metal right beside each boundary is stripped of the chromium it needs to stay passive.
A weld puts a band of the heat-affected zone through that range on every pass. In standard-carbon 316 the band can sensitize, and in service it shows up as “weld decay”: a line of intergranular attack running parallel to the weld, a short distance away from it, while the weld itself and the parent metal look fine. Heavy sections, slow cooling, high heat input and multipass welds make it more likely; thin sheet welded quickly often escapes.
The low-carbon grade does not make sensitization impossible, but it delays it far beyond the time a weld spends in the range. The same association notes that low-carbon 316L and the stabilized grades only delay the onset and do not eliminate it under prolonged exposure at sensitizing temperatures.
Welding is not the only trigger. Brazing, hot forming, stress relieving and slow cooling from a heat treatment do the same thing. The association’s guidance on stress relieving austenitic stainless steels advises avoiding the 480 to 900 °C range as a general guideline, and states that the low-carbon 304L and 316L types should not be at risk of corrosion sensitization during stress relieving. If a machined part will be stress relieved for dimensional stability, that alone is a reason to call 316L.
To prove a lot is not susceptible, the test is ASTM A262, the practices for detecting susceptibility to intergranular attack in austenitic stainless steels. Practice A, an oxalic acid etch, is a quick screen; Practice E, the copper and copper sulfate in sulfuric acid test followed by a bend, is commonly written into purchase orders. Name the practice and whether specimens are tested as received or after a sensitizing treatment.
What is dual-grade 316/316L bar, and does it meet a 316 callout?
Dual-grade bar is a single heat whose chemistry meets the 316L carbon limit and whose mechanical properties also meet the higher 316 minimums, so the mill report lists both grades and both UNS numbers. It satisfies a drawing that calls 316 and a drawing that calls 316L.
Mills make it by melting to the low-carbon limit and recovering the strength another way, typically with a controlled nitrogen addition and the cold finishing that bar goes through anyway. Because one heat can be sold against either callout, it is a convenient way for stockholders to cover both grades with one inventory, which is why a 316 order is often filled with dual-grade bar.
The logic for accepting it is simple once you separate the two limits. A 316 callout cares about the 316 carbon cap and the 316 strength minimums; dual-grade bar is below the cap and above the minimums. A 316L callout cares about the low-carbon cap and the lower 316L strength minimums; dual-grade bar meets both. The only callout it does not automatically meet is one with requirements outside the grade, such as a tighter sulfur range, a ferrite limit, an implant specification or an elevated-temperature grade.
What to check on the certificate: both UNS numbers, S31600 and S31603, should appear; the carbon result should be at or below the 316L limit; the yield and tensile results should clear the 316 minimums; and the specification line should name the standard you called, for example ASTM A276 or ASTM A479, the bar specification for boilers and other pressure vessels. If you need the heat chemistry and tests confirmed by a department independent of production, ask for an EN 10204 type 3.1 inspection certificate rather than a plain declaration of compliance.
Does 316L machine differently from 316?
Not in any way that should drive the grade choice. Both are austenitic, both work harden under the tool and both make long, stringy chips, so a part that machines well in one machines well in the other.
The usual stainless rules apply to both: sharp positive-rake tools, feeds heavy enough to get under the work-hardened layer left by the previous pass, rigid setups and generous coolant. Dwelling or rubbing is what ruins a 316 or 316L part, not the grade letter. Neither grade has a widely used free-machining sulfur version the way 304 has 303, and the guide on 303 vs 304 stainless explains why adding sulfur would cost the chloride resistance that is the reason for choosing 316 in the first place.
After machining, either grade needs the same passivation to remove free iron left by tooling. ASTM A967 is the specification most purchase orders cite, and the passivation guide covers the nitric and citric options and the acceptance tests. One caution for welded 316 assemblies: passivation restores the surface after machining, but it does not reverse sensitization in the heat-affected zone. Only a full solution anneal does that, and an anneal after final machining will move dimensions on a precision part.
When is neither 316 nor 316L the right grade?
When the part runs hot under load, goes into the body, or sits in warm seawater. Each of those has its own grade or specification, and writing plain 316 or 316L on the drawing will not get it.
- Elevated-temperature strength. For pressure parts that run hot, the high-carbon variant 316H keeps carbon between 0.04% and 0.10% per ASTM A240, deliberately, to hold creep strength. Pressure-design codes also limit how high a temperature the low-carbon grade can be used at, so check the code before choosing 316L for hot service.
- Stabilized grades. 316Ti (1.4571 in EN 10088-3) ties carbon up with titanium instead of reducing it. It is common in European specifications for welded parts that also see heat in service; treat it as its own grade, not an equivalent of 316L.
- Surgical implants. Implant bar is bought to ASTM F138, which covers wrought 18 chromium, 14 nickel, 2.5 molybdenum bar and wire under its own UNS number, S31673, with tighter cleanliness and composition control than commodity 316L. A drawing for an implant should name F138, not 316L.
- Seawater and warm chlorides. The British Stainless Steel Association’s note on 316, 304 and 303 in seawater describes the corrosion resistance of the 316 types in seawater as limited, mainly by crevice and pitting attack, with crevice risk rising as the water warms; it does not recommend 304 or 303 there at all. The same note recommends the low-carbon 316L types for welded seawater parts to avoid attack next to the weld, but 316L does not improve crevice or pitting resistance, so warm-water service calls for a higher-alloy grade.
What should the drawing say?
Name the grade by UNS number, the product specification and the condition, then say explicitly whether dual-grade bar is acceptable. Add the passivation and certificate requirements in the same note so they travel with the drawing.
For a welded assembly or any part that will see brazing or stress relief:
MATERIAL: STAINLESS STEEL UNS S31603 (316L) BAR PER ASTM A276/A276M, ANNEALED. DUAL-GRADE 316/316L ACCEPTABLE. PASSIVATE PER ASTM A967. MILL TEST REPORT TO EN 10204 TYPE 3.1 REQUIRED.
For a machined, non-welded part where the 316 strength minimums are used in the design:
MATERIAL: STAINLESS STEEL UNS S31600 (316) BAR PER ASTM A276/A276M, ANNEALED. DUAL-GRADE 316/316L ACCEPTABLE; 316L ALONE NOT ACCEPTABLE.
For a pressure-retaining part, replace A276 with A479 and keep the dual-grade sentence.
The mistakes that cause trouble are predictable:
- “SS316” with no specification. It invites bar made to any standard in any condition, and the certificate cannot be checked against anything.
- Calling plain 316 on a welded part. Standard-carbon bar is still legal against that callout, so the low-carbon property you were counting on is not guaranteed.
- Calling 316L and rejecting dual-grade bar. The dual-grade product meets every 316L limit; rejecting it usually just delays the order.
- “316L or equivalent.” Equivalent to what, under which standard? If EN 1.4404 or JIS SUS316L is acceptable, write it.
- Plate specifications on bar parts. A240 is for flat products. A turned part comes from bar, so cite A276 or A479.
What should the RFQ ask for on a 316 or 316L part?
Ask the supplier to quote to the grade and specification on the drawing, to say which bar they intend to buy, and to send the mill certificate with each lot. Settle equivalents and the intergranular test, if any, before the quote rather than after first articles.
A complete stainless RFQ states the grade and UNS number, the bar specification and condition, whether dual-grade, EN or JIS equivalents are acceptable, whether the part is welded or heated after machining, the passivation specification and test, any ASTM A262 practice, and the certificate type. The RFQ guide lists the rest of the package, and the EN 10204 guide explains what a 3.1 report proves that a 2.2 does not.
On our side, be aware of what is and is not standard here. The bar list on the CNC turning page shows the materials running today, and stainless is not among them, so a 316 or 316L part is something to raise at drawing review rather than assume. Passivation is not on the menu of finishes our partner plants apply, as listed on the surface finishing page, so raise it at drawing review and the quote will name where each step is done. Material certification with a traceable source for the grade used is available on request, as listed on the quality page; ISO 9001 is in progress, not held. If the material and finish fit, send the drawing through the quote form.
Frequently asked
Is 316L more corrosion resistant than 316?
Only where heat has been involved. On an unwelded, unheated part the two resist pitting and general corrosion the same way, because their chromium and molybdenum ranges are the same. Next to a weld, or after a stress relief or braze, 316L keeps its resistance where standard-carbon 316 may have sensitized.
Can I substitute 316L for 316 without a drawing change?
Not plain 316L, because its minimum yield and tensile strength are lower than the 316 values, and a strength-critical design may depend on them. Dual-grade 316/316L bar is the substitution that meets the 316 callout, since it clears both the 316 strength minimums and the 316L carbon limit.
Is 316 or 316L magnetic?
In the annealed condition both are essentially nonmagnetic. Heavy cold work, such as cold heading or some cold-drawn bar, can make them slightly magnetic. If magnetic permeability matters, put the requirement and the measurement method on the drawing instead of relying on the grade name.
Which filler metal goes with 316L?
Welders normally use a low-carbon 316L filler, classified under AWS A5.9 for bare wire and rod, so the weld metal keeps the same low-carbon protection as the base metal. If the assembly drawing calls a weld procedure, the filler is named there rather than on the machined detail drawing.
Does a mill certificate marked 316/316L mean the material is mixed?
No. It means one heat, tested once, meets the requirements of both grades. Check that the heat number on the certificate matches the bar marking and that the carbon and strength results support both grade names.
Sources
- ASTM A276/A276M-25, Standard Specification for Stainless Steel Bars and Shapes (scope), ASTM International, 2025
- ASTM A240/A240M-26, Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications (scope), ASTM International, 2026
- ASTM A479/A479M-25, Standard Specification for Stainless Steel Bars and Shapes for Use in Boilers and Other Pressure Vessels (scope), ASTM International, 2025
- ASTM A262-15(2021), Standard Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels (scope), ASTM International, 2021
- ASTM A967/A967M-25, Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts (scope), ASTM International, 2025
- ASTM F138-19, Standard Specification for Wrought 18Chromium-14Nickel-2.5Molybdenum Stainless Steel Bar and Wire for Surgical Implants (UNS S31673) (scope), ASTM International, 2019
- EpicFail: Polythionic Acid Stress Corrosion Cracking, British Stainless Steel Association, accessed October 2026
- Stress relieving heat treatments for austenitic stainless steels, British Stainless Steel Association, accessed October 2026
- Selection of 316, 304 and 303 types of stainless steels for seawater applications, British Stainless Steel Association, accessed October 2026