The practical answer to 304 vs 316 stainless steel is a single question: will the part meet chlorides? Salt spray, seawater, de-icing salt, chlorinated cleaning agents, brine, sweat or coastal air all attack the passive layer that protects stainless. 316 contains roughly 2 to 3 percent molybdenum, and molybdenum is what resists that specific attack. Where chlorides are absent, 304 performs essentially as well and costs less.
316L is not a third corrosion grade so much as a welding grade. It is 316 with the carbon capped at about 0.03 percent, which prevents chromium carbides from forming at grain boundaries during welding. That precipitation, known as sensitisation, strips chromium from the surrounding metal and leaves the heat-affected zone vulnerable to intergranular corrosion. If your part is welded and will live in a corrosive environment, specify 316L rather than 316.
Everything else — formability, machinability, appearance, hygiene, strength — is close enough between the grades that it rarely decides the choice on its own. What follows is the detail behind that summary.
304 vs 316 stainless steel: composition and why molybdenum matters
All three grades are austenitic stainless steels, non-magnetic in the annealed condition, and all rely on a chromium oxide passive film for corrosion resistance. The difference is what happens when that film is locally broken.
| Property | 304 / 304L | 316 | 316L |
|---|---|---|---|
| Chromium | 18.0 – 20.0% | 16.0 – 18.0% | 16.0 – 18.0% |
| Nickel | 8.0 – 10.5% | 10.0 – 14.0% | 10.0 – 14.0% |
| Molybdenum | — | 2.0 – 3.0% | 2.0 – 3.0% |
| Maximum carbon | 0.08% (304L: 0.03%) | 0.08% | 0.03% |
| Approximate PREN | 18 – 20 | 24 – 26 | 24 – 26 |
| Tensile strength, annealed | ≥ 515 MPa | ≥ 515 MPa | ≥ 485 MPa |
| Yield strength, annealed | ≥ 205 MPa | ≥ 205 MPa | ≥ 170 MPa |
| Elongation | ≥ 40% | ≥ 40% | ≥ 40% |
| Chloride resistance | Moderate | Good | Good |
| Post-weld corrosion risk | Higher in 304 | Higher than 316L | Lowest |
| Relative cost | Baseline | Typically higher | Typically higher |
PREN — the pitting resistance equivalent number, calculated as %Cr + 3.3 × %Mo + 16 × %N — is a convenient single figure for comparing pitting resistance. It is a ranking tool, not a design limit: a higher PREN means better resistance to chloride pitting, but it does not tell you the part will survive a specific environment. Use it to compare candidates, then validate against the actual service condition.
Pitting and crevice corrosion in practice
Chloride attack on stainless is rarely uniform. It is localised, and that is what makes it dangerous — a pit can perforate a wall while the surrounding surface still looks perfect.
Pitting
Chloride ions penetrate the passive film at a weak point, and a small anodic site develops that keeps dissolving. Higher temperature, higher chloride concentration and stagnant conditions all accelerate it. 304 is noticeably more susceptible than 316 in this regard.
Crevice corrosion
The same mechanism, concentrated in a gap where the electrolyte cannot exchange: under a gasket, in an overlapped joint, beneath a washer, in an unfinished weld root. Crevice attack begins at lower chloride levels than open-surface pitting, which is why joint design matters as much as grade selection. Continuous welds instead of intermittent ones, full penetration rather than lap joints, and radiused internal corners all reduce crevice risk. If your design is full of crevices, upgrading from 304 to 316 buys you less than fixing the geometry.
Why 316L exists: welding and sensitisation
When austenitic stainless is held between roughly 450 °C and 850 °C — which every weld’s heat-affected zone passes through — carbon migrates to grain boundaries and combines with chromium to form chromium carbides. The metal immediately beside those carbides is now chromium-depleted and no longer properly stainless. Corrosion then follows the grain boundaries, and a weld that looks sound can fail from within.
Capping carbon at 0.03 percent removes most of the available carbon and largely prevents the reaction. That is the whole purpose of the L grades. Practical guidance:
- Welded assembly plus corrosive service: specify 316L.
- Welded assembly in a benign indoor environment: 304 is usually acceptable, 304L if section thickness is significant.
- Unwelded parts — stamped, drawn, bent or machined only: the L distinction is largely irrelevant, so choose on chloride exposure alone.
Post-weld treatment matters just as much as grade. Welding leaves heat tint, and heat tint is a chromium-depleted oxide layer that reduces corrosion resistance wherever it remains. Pickling removes it chemically; passivation then restores the protective film. On welded stainless assemblies we pickle and passivate where the drawing calls for it — but it must be called for, because it is a specified operation, not an automatic one.
Forming and machining: 304 vs 316 stainless steel in the workshop
Deep drawing and bending
Both 304 and 316 draw well, with elongation typically at or above 40 percent in the annealed condition. Austenitic stainless work-hardens strongly, which is an advantage for deep shapes because the material resists localised thinning, and a disadvantage because forming loads rise quickly and deep parts may need interstage annealing.
316 requires somewhat higher forming loads than 304 and springs back slightly more. For bending, both grades typically need a minimum inside radius of about one material thickness in thinner gauges, rising to around 1.5 times thickness as the sheet gets heavier. Neither grade tolerates sharp bends the way annealed aluminium does. Our deep drawing line runs both grades regularly.
Machining
All three grades are gummy, work-harden rapidly under a dull tool and produce stringy chips. The rules are the same across the family: sharp tooling, positive rake, rigid setup, generous coolant, and a consistent feed that keeps the tool cutting beneath the work-hardened layer rather than rubbing on it. 316 is marginally more difficult than 304; the L variants machine much like their parent grades.
When 304 is genuinely enough
Over-specification is common, and it costs money on every part for the life of the programme. 304 is normally sufficient for:
- Indoor equipment housings, panels, enclosures and chassis.
- Kitchen and food-service equipment that contacts food but is cleaned with conventional non-chloride detergents.
- Architectural and decorative components away from coastal exposure.
- Structural brackets, frames and mounting hardware in dry environments.
- Storage vessels for non-chloride contents.
Specify 316 or 316L when the part will face:
- Marine, coastal or offshore exposure.
- Brine, seawater or chloride-bearing process fluids.
- Chlorinated or halide-based cleaning and sterilisation chemicals.
- Pharmaceutical, laboratory or medical processing environments.
- De-icing salt exposure on outdoor or transport equipment.
- Elevated-temperature service in the presence of chlorides.
A useful discipline: write the actual service environment on the drawing rather than only the grade. If the drawing says “316L, marine splash zone, chlorinated wash-down”, a supplier can flag when the design’s crevices matter more than the grade. If it says only “stainless”, the review cannot happen. The same principle applies to food equipment parts, where cleaning chemistry frequently drives the grade decision more than the food contact itself.
Certification and traceability
For any part where grade matters, ask for EN 10204 3.1 mill test certificates. A 3.1 certificate reports chemical composition and mechanical properties traceable to the mill heat number, issued by the manufacturer’s authorised inspection representative — which means the grade is documented rather than asserted. We supply them on request for every material we process.
Composition and mechanical property limits for these grades are set by ASTM A240. Material substitution is a real risk in low-cost sourcing, and 304 supplied against a 316 order will pass a visual inspection and most simple tests. Traceability documentation, backed by a quality system, is the practical defence. Ours runs under ISO 9001:2015, registration 34025Q30296R0S, which can be verified independently at cnca.gov.cn.
Frequently Asked Questions
What is the main difference between 304 vs 316 stainless steel?
316 contains 2 to 3 percent molybdenum, which substantially improves resistance to chloride pitting and crevice corrosion; 304 contains none. 304 has slightly higher chromium, 316 has more nickel. In chloride-free environments the two perform similarly, which is why 304 remains the correct choice for most indoor applications.
Is 316L stronger than 316?
No, 316L is slightly weaker in the annealed condition, with typical minimum yield around 170 MPa against 205 MPa for 316, because the lower carbon content reduces solid-solution strengthening. The difference rarely matters in sheet metal fabrication. 316L is chosen for weldability and post-weld corrosion resistance, not strength.
Do I need 316L instead of 316 for a welded part?
Yes, if the welded part will see a corrosive environment. The low carbon content prevents chromium carbide precipitation in the heat-affected zone, which is what causes intergranular corrosion after welding. For welded parts in dry indoor service, standard 316 or even 304 is generally acceptable.
How much more does 316 cost than 304?
316 typically costs more than 304 because of the molybdenum content and higher nickel, and the gap moves with nickel and molybdenum commodity prices rather than staying fixed. Because the premium is ongoing across every part produced, over-specifying the grade is a recurring cost rather than a one-off. Ask for both grades to be quoted if the environment is borderline.
Can 304 and 316 be deep drawn?
Yes, both draw well, with elongation typically at or above 40 percent annealed and strong work-hardening that helps resist localised thinning. 316 needs somewhat higher forming loads and shows slightly more springback. Deep parts in either grade may require interstage annealing between redraw operations.
Does stainless steel need passivation after fabrication?
It is strongly recommended after welding, grinding or machining, because those operations leave heat tint, embedded iron particles or a disturbed surface that reduces corrosion resistance. Pickling removes heat tint chemically and passivation restores the chromium oxide film. Specify it explicitly on the drawing, since it is a defined operation rather than an automatic step.
Send the drawing with the service environment noted
Grade selection is much easier to get right when the supplier knows what the part will actually face. Send your drawing along with the operating environment, cleaning regime and any documentation requirements, and an engineer will confirm the grade, flag any crevice-prone geometry and return a quotation within 3 business hours. Email xcwystamping@xcwybj.com or use the quote request form.
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