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SUS316 vs SUS316L for Machined Parts: Carbon, Welding and Finish

Materials / 28 Aug 2026

SUS316 and SUS316L arrive on drawings almost interchangeably, and the L is often added out of habit. Sometimes it is essential. Sometimes it is a specification that narrows your stock options and buys nothing.

Here is what actually changes, and how to tell which one your part needs.

The only real difference is carbon

	SUS316	SUS316L
Carbon, max	0.08 %	0.030 %
Chromium	16.0 to 18.0 %	16.0 to 18.0 %
Nickel	10.0 to 14.0 %	12.0 to 15.0 %
Molybdenum	2.00 to 3.00 %	2.00 to 3.00 %
Yield strength, typical	around 205 MPa	around 170 MPa
EN number	1.4401	1.4404
Machinability index	around 36	around 36

The molybdenum, which is the whole reason to choose a 316 over a 304, is identical. Corrosion resistance in service is essentially the same for both, with one exception covered below.

What the low carbon is for

When austenitic stainless is held between roughly 450 and 850 degC, chromium and carbon combine into chromium carbides at the grain boundaries. Those carbides pull chromium out of the surrounding metal, leaving a chromium depleted band that no longer passivates. The result is intergranular corrosion: the material rusts along the grain boundaries, often invisibly, and eventually falls apart in sheets.

The part of a weld that sits in that temperature range while the weld itself cools is the heat affected zone. This is where sensitisation happens, and it is why the phenomenon is usually called weld decay.

Cap the carbon at 0.030 % and there is not enough of it to form a damaging amount of carbide during a normal weld cycle. That is the entire purpose of the L grade.

So when do you actually need it

Specify SUS316L when:

The part is welded and cannot be solution annealed afterwards
The part is welded and then used in a corrosive environment
The part is brazed or held for any length of time in the 450 to 850 degC band
The customer specification or an industry standard requires it, for example pharmaceutical and semiconductor wetted parts, where 316L is effectively the default and arguing is not worth the time
Electropolishing is specified, because a cleaner, lower carbon surface polishes more consistently

SUS316 is sufficient when:

The part is machined from bar or plate and never welded
Service temperature stays below about 400 degC
You need the slightly higher yield strength
Availability or price in your size favours it

The one case where 316L is worse

Above roughly 500 degC in continuous service, the low carbon that helps during welding hurts during operation. Carbon contributes to creep strength, so SUS316L has lower allowable stresses at elevated temperature than SUS316. Pressure vessel codes reflect this.

If your part runs hot continuously, do not reach for the L grade by reflex. Check the temperature, and if it is genuinely high, look at SUS321 instead, which is titanium stabilised and holds up in exactly the range where both 316 grades start to struggle.

Both of them on the machine

Whichever you pick, the machining story is the same, and it is not the same as SUS304.

Machinability index sits around 36, against 45 for SUS304 and 78 for SUS303. Expect roughly 20 to 30 % longer cycle time than a comparable SUS304 part, and faster insert wear than that number alone suggests.

The reasons:

Molybdenum raises hot strength. The alloy keeps its strength at the temperature the cutting edge reaches, which is the opposite of helpful.
Thermal conductivity is about 16 W per metre kelvin. Heat stays in the tool rather than leaving in the chip.
It is gummy. Long continuous chips weld to the rake face, tear away and take coating with them.
It work hardens. A rubbing tool or a light spring pass leaves a hardened skin that the next pass has to fight.

What a shop that runs it regularly does differently: heavier feed than instinct suggests, depth of cut always below the previous pass’s hardened layer, sharp edges replaced on a schedule rather than on failure, high pressure coolant where the machine supports it, and 0.3 to 0.5 mm left on diameters for a finishing pass that cuts fresh material.

Why 316L parts usually cost more than the grade alone explains

316L rarely arrives on a drawing alone. It arrives with company:

A surface finish target, often Ra 0.8 or better on wetted faces
Passivation, normally to ASTM A967 or AMS 2700
Electropolishing on pharma and semiconductor parts
A certificate, usually EN 10204 3.1 with heat lot traceability
Sometimes a magnetic permeability limit, because cold work raises permeability on austenitic grades

Each of those is real cost, and several are outside processes with their own minimum lots and lead times. When a 316L quote looks high next to a 304 quote, the grade is usually only part of the gap.

Ask for what the part needs and nothing more. Passivation on a part that never sees moisture is money spent on paperwork.

What to put on the drawing

SUS316L per JIS G 4303
EN 1.4404 acceptable
Mill certificate to EN 10204 3.1, heat lot traceable
Passivate per ASTM A967, citric
Ra 0.8 max on wetted surfaces, as machined elsewhere

That is a complete specification. Every shop reading it prices the same part.

For the wider grade comparison, see SUS303 vs SUS304 vs SUS316. For what passivation actually does and which method to ask for, see passivation of machined stainless parts.

Ready to price a part? Get a quote. The part is placed with a shop in our network that runs these grades weekly, and inspected before it ships. Priced quote within 24 business hours.

Questions

What does the L in SUS316L mean?

Low carbon. SUS316 allows up to 0.08 per cent carbon, SUS316L caps it at 0.030 per cent. Everything else in the chemistry is essentially the same.

Do I need SUS316L if the part is not welded?

Usually not. The low carbon exists to stop chromium carbides forming at grain boundaries during welding. A machined part that is never welded and never held in the 450 to 850 degC range gets no benefit from it.

Is SUS316L weaker than SUS316?

Slightly. Lower carbon means lower yield and tensile strength, typically around 170 MPa yield against 205 MPa. For most machined parts the difference is irrelevant, but check it if the part is loaded.

Which one machines better?

There is no meaningful difference. Both sit around 36 on the standard machinability index, both are gummy, both work harden. Choose on service requirements, not on machinability.

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