In short: Type 316 is the second most widely used austenitic stainless steel and the standard molybdenum-bearing grade. It keeps the ductile, non-magnetic FCC austenite structure of 304, but adds 2–3% molybdenum that dramatically improves resistance to chloride-induced pitting and crevice corrosion. That single change makes 316 the default choice for seawater, coastal air, chemical processing, pharmaceutical and medical-implant service. Where 304 stops at fresh water and mild atmospheres, 316 keeps going into salt.
What 316 Stainless Steel Is
Type 316 is the austenitic stainless steel you reach for the moment chlorides enter the picture. It is built on the same iron–chromium–nickel base as 304, but with one decisive addition — 2 to 3% molybdenum — and that is what earns it the description of "the standard molybdenum-bearing grade, second in importance to 304."[1]
Because it is traded worldwide, the same alloy carries several names. In the Unified Numbering System it is UNS S31600; in the European EN system it is 1.4401 (X5CrNiMo17-12-2); and in Japanese practice it is SUS 316. All refer to the same molybdenum-bearing austenitic stainless steel.[1] The molybdenum "gives 316 better overall corrosion-resistant properties than Grade 304, particularly higher resistance to pitting and crevice corrosion in chloride environments" — which is precisely why 316 dominates marine, chemical and medical work.[1]
Chemical Composition
The performance of 316 flows directly from its chemistry: enough chromium and nickel to hold a ductile austenitic structure, plus the molybdenum that sets it apart from 304. The chart below shows the balance by weight — note the molybdenum slice, the element 304 does not have — and the table lists the specified ranges per the ASTM A240 grade limits.[1]
| Element | Symbol | Content (wt%) | Role |
|---|---|---|---|
| Chromium | Cr | 16–18 | Forms the self-healing passive oxide film — the source of "stainless" |
| Nickel | Ni | 10–14 | Stabilises the ductile, non-magnetic austenite phase (higher than 304 to offset Mo) |
| Molybdenum | Mo | 2–3 | The defining addition — strengthens the passive film against chloride pitting and crevice attack |
| Carbon | C | ≤ 0.08 | Kept low to limit carbide precipitation and preserve corrosion resistance |
| Manganese | Mn | ≤ 2 | Deoxidiser; aids hot working and austenite stability |
| Silicon | Si | ≤ 0.75 | Deoxidiser; assists oxidation resistance |
| Iron | Fe | Balance | Base metal |
Specified composition limits per the ASTM A240 datasheet (standard 316 carbon ≤ 0.08; the low-carbon 316L variant is ≤ 0.030).[1]
Crystal Structure: FCC Austenite
Stainless steel is an alloy — a solid solution of several elements in iron — so it has no molecular formula. The right way to describe 316 is by its crystal structure: at room temperature it is austenite, a face-centred-cubic (FCC) arrangement of atoms with a unit cell that holds atoms at every corner and at the centre of every face. The molybdenum dissolves into this lattice without changing the phase — 316 is FCC austenite, exactly like 304.[1]
Plain low-alloy steels are body-centred-cubic (BCC) ferrite, which is magnetic and far less ductile. The 10–14% nickel in 316 stabilises the FCC austenite phase all the way down to room temperature, and that single fact explains the grade's signature behaviour: excellent ductility and deep-drawing formability, plus the fact that fully annealed 316 is essentially non-magnetic. The molybdenum sits dissolved in this same lattice, sharpening corrosion resistance without disturbing the phase.[1]
As with all austenitic grades, that non-magnetic character can shift slightly under heavy cold work as a little of the metastable austenite transforms to magnetic α′-martensite — but 316's richer nickel and molybdenum make it more stably austenitic than 304, so the effect is comparatively mild.[1]
Why It Beats Chlorides: Molybdenum in the Passive Film
The "stainless" in stainless steel comes from chromium. Once the chromium content rises above roughly 11%, the alloy spontaneously grows an ultra-thin, chromium-rich oxide layer on its surface — only a few nanometres thick, yet dense and tightly bonded. This passive film is what stands between the metal and the environment, and like 304 it re-forms when scratched.[7]
What sets 316 apart is what happens *inside* that film. Nanometre- and atomic-scale analysis of 316L shows that molybdenum becomes enriched together with chromium in the passive film and combines several effects to enhance resistance to chloride-induced breakdown: enriched as Mo(VI) in the outer exchange layer it impedes the deep penetration of Cl⁻ ions, while dispersed as Mo(IV) at the inner interface it protects the chromium-oxide barrier against chloride entry at its defect sites.[2] In direct comparisons of 304 and 316 in chloride media, the benefit of molybdenum is assigned to Mo⁶⁺ within the passive film — rendering it more stable against attack by aggressive Cl⁻ ions — and to insoluble molybdenum compounds that form inside any pit and help it re-passivate.[3]
The chromium oxide film itself still heals like 304's: scratch-and-recover experiments covering both AISI 304 and 316 measure a reconstruction time of about 2 hours, with the regrown film markedly enriched in chromium relative to iron.[7] The molybdenum simply makes that film much harder for chlorides to defeat in the first place.
Mechanical & Physical Properties
The values below are the specified/typical values per the ASTM A240 datasheet for annealed 316; the strength figures are specified minimums for the grade.[1]
| Tensile strength (MPa) | ≥515 |
| Yield strength (MPa) | ≥205 |
| Elongation (%) | ≥40 |
| Hardness | ≤217 HB |
| Density (g/cm³) | 8.0 |
| Elastic modulus (GPa) | 193 |
| Magnetic response | Non-magnetic (annealed) |
The mechanical profile is nearly identical to 304 — moderate strength paired with very high ductility, a minimum of 40% elongation that follows directly from the FCC austenite structure described earlier.[1] That ductility is what lets 316 be deep-drawn, spun and roll-formed into tanks, tube and marine hardware without cracking. The point of choosing 316 is never extra strength; it is the molybdenum-driven corrosion resistance that the otherwise-similar 304 cannot match.[1]
Key Characteristics
- Chloride & pitting resistance. The defining trait — 2–3% molybdenum makes the passive film far more resistant to chloride pitting and crevice corrosion than 304, the reason 316 is the marine and chemical standard.
- Formability. The FCC austenite gives outstanding cold-forming behaviour — deep drawing, bending, spinning and roll forming are all straightforward, just as with 304.
- Weldability. 316 welds readily by all common methods; for welded assemblies in corrosive service, the low-carbon variant 316L avoids carbide precipitation in the heat-affected zone.
- Hygiene & cleanability. The smooth, non-porous passive surface resists bacterial harbourage and stands up to repeated cleaning and sterilisation — a key reason it dominates pharmaceutical and medical equipment.
- Biocompatibility. 316L is well established in surgical and implant use, where its corrosion resistance and tissue compatibility are essential.
How 316 Is Made
Production starts by melting scrap and ferroalloys — including ferro-molybdenum to hit the 2–3% Mo target — in an electric arc furnace, then refining the melt in an argon–oxygen decarburisation (AOD) vessel to drive carbon down while preserving chromium. The steel is then cast, hot- and cold-rolled to gauge, annealed to restore the soft austenitic structure, and finally pickled and passivated to clean the surface and re-establish a uniform passive film before finishing.
316 vs 304
The most common cross-shopping question in stainless steel is 316 versus 304. The structural difference is small but decisive: 316 adds 2–3% molybdenum on top of the same austenitic base, and that molybdenum dramatically improves resistance to chloride pitting and crevice corrosion.
The mechanism is well documented. In chloride media, molybdenum's benefit is assigned to Mo⁶⁺ present within the passive film, rendering it more stable against breakdown by aggressive Cl⁻ ions, and to insoluble molybdenum compounds that form inside an incipient pit and help it re-passivate.[3] Atomic-scale work on 316L confirms molybdenum, co-enriched with chromium, impedes deep Cl⁻ penetration and guards the oxide barrier's defect sites.[2] For everything that does not see heavy chloride loads, 304 remains the cost-effective generalist; the moment salt appears, 316 is the answer.
Variants & Related Grades
316 anchors a small family of closely related grades, each tuned for a particular service:
- [316L](/en/materials/stainless-steel/316l) — the low-carbon version (C ≤ 0.030%). The reduced carbon suppresses chromium-carbide precipitation during welding, giving better resistance to intergranular corrosion in welded assemblies — the default for welded marine and seawater hardware, and the form most studied for medical implants.
- 316Ti — a titanium-stabilised version; the titanium ties up carbon as stable titanium carbides, preserving corrosion resistance through welding and sustained moderate-temperature service.
- 316H — the high-carbon version, with carbon held in a controlled higher band to provide better creep and high-temperature strength for elevated-temperature pressure equipment.
The detailed 316L page is linked above for readers who need the specific weld or implant data; for general molybdenum-grade work the standard 316 covered here is the usual starting point.
Applications by Industry
Because the molybdenum unlocks chloride resistance on top of 304's hygiene and formability, 316 is the grade that goes where salt and aggressive chemistry rule it out.
Marine & Coastal
Boat rigging, deck fittings, railings, propeller shafts, coastal balustrades and seafront façades are classic 316 territory. In long-term natural-seawater field exposure, 316L does corrode by crevice and biofouling-driven attack — and honestly, the corrosion rate ranks 316L well above the duplex grades, so for the most aggressive permanently-immersed seawater service designers step up to a duplex steel such as 2205 or 2507.[4] For the vast majority of marine and coastal hardware, though, 316/316L is the cost-effective standard.
Chemical & Process
Storage tanks, pressure vessels, heat exchangers and pipework handling chloride-bearing and aggressive chemistries rely on 316's molybdenum-strengthened passive film, where 304 would pit. It is a workhorse across chemical, petrochemical, pulp-and-paper and desalination plant.
Medical & Pharmaceutical
316L is widely used in orthopedic and dental implants, where its corrosion resistance in chloride-rich body fluids and its mechanical reliability are essential.[5] Cytocompatibility studies confirm that uncoated 316L allows cells to adhere, grow and differentiate on its surface, supporting its use even in devices that contact nerve tissue.[6] The same molybdenum-driven corrosion resistance also makes 316 the standard for pharmaceutical process equipment and high-salt food processing.
Forms & Finishes
Common product forms:CoilSheetPlateTubeBar
Surface finishes:2BBANo.4HLMirror
As a rule of thumb, a smoother finish leaves fewer crevices for contaminants to lodge in, which translates to marginally better corrosion resistance as well as easier cleaning — a benefit that matters even more in the chloride service where 316 is chosen.
References
- Stainless Steel – Grade 316 (UNS S31600). AZoM (materials datasheet based on the ASTM/AISI grade system). azom.com/article.aspx?ArticleID=863
- Molybdenum effects on the stability of passive films unraveled at the nanometer and atomic scales. Maurice V., Marcus P. npj Materials Degradation, vol. 7 (2023). doi.org/10.1038/s41529-023-00418-6
- Pitting corrosion behaviour of austenitic stainless steels – combining effects of Mn and Mo additions. Pardo A., Merino M.C., Coy A.E., Viejo F., Arrabal R., Matykina E. Corrosion Science, vol. 50, 1796–1806 (2008). doi.org/10.1016/j.corsci.2008.04.005
- A comparison study of crevice corrosion on typical stainless steels under biofouling and artificial configurations. Zhang Z., Li Z., Wu F., Xia J., Huang K., Zhang B., Wu J. npj Materials Degradation, vol. 6 (2022). doi.org/10.1038/s41529-022-00301-w
- Manufacturing, Microstructure, and Mechanics of 316L SS Biomaterials by Laser Powder Bed Fusion. Journal of Functional Biomaterials, vol. 16, 280 (2025). doi.org/10.3390/jfb16080280
- Cytocompatibility Study of Stainless Steel 316L Against Differentiated SH-SY5Y Cells. Zingkou E., Kolianou A., Angelis G., Lykouras M., Orkoula M., Pampalakis G., Sotiropoulou G. Biomimetics, vol. 10, 169 (2025). doi.org/10.3390/biomimetics10030169
- Reconstruction of the Passive Layer of AISI 304 and 316 Steel After Scratching. Charazińska S., Sikora A., Malczewska B., Lochyński P. Materials, vol. 17, 6238 (2024). doi.org/10.3390/ma17246238