316 Stainless Steel
Also: AISI 316, UNS S31600, 316L (UNS S31603), A4 stainless (fasteners), 1.4401, X5CrNiMo17-12-2, 1.4404 (316L), SUS316, marine grade stainless, CF8M (cast 316), CF3M (cast 316L), 316LVM (implant grade)
316 is 304 with 2-3% molybdenum: the marine and chemical-service austenitic stainless, with far better chloride pitting resistance. 316L for welds. Values annealed.
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At a glance
| Density | 8 g/cm³ (0.289 lb/in³) |
|---|---|
| Tensile strength | 515-620 MPa (75-90 ksi); ASTM A240 minimum 515 MPa (75 ksi), 485 MPa (70 ksi) for 316L |
| Yield strength | 205-290 MPa (30-42 ksi); minimum 205 MPa (30 ksi), 170 MPa (25 ksi) for 316L |
| Hardness | 70-90 HRB (about 150-200 HB); ASTM A240 maximum 217 HB (95 HRB) |
| Elongation | 40-55% (minimum 40%) |
| Modulus of elasticity | 193 GPa (28 Msi) |
| Thermal | Melts at 1375-1400 °C (2500-2550 °F); thermal conductivity ~16 W/m·K; expansion ~16 um/m·K; scaling resistance to about 925 °C (1700 °F) continuous, 870 °C (1600 °F) intermittent |
| Composition | Fe, 16-18% Cr, 10-14% Ni, 2-3% Mo, up to 0.08% C (316L up to 0.03%), up to 2% Mn, up to 1% Si, up to 0.1% N |
Typical values, Annealed (solution treated at 1040-1120 °C / 1900-2050 °F and water quenched). Confirm against the mill certificate and the purchase spec.
- MachinabilityFair
- About 36-45% of B1112, a shade tougher and gummier than 304 because of the molybdenum. Same rules: sharp positive-rake carbide, rigid setup, steady feed, no dwelling. There is no free-machining 316; 303 is the turned-part alternative when the corrosion budget allows.
- WeldabilityExcellent
- Welds by TIG, MIG, laser and resistance processes with 316L filler and no preheat. Use 316L base metal for anything welded over about 5 mm (3/16"). Back-purge tube and pipe, and pickle or electropolish heat tint off welds that will see chlorides.
- FormabilityGood
- Bends, rolls and draws like 304 with a little less stretch; bend at 1-2t inside radius with springback allowance. Deep draws that 304 does in one hit may need an intermediate anneal in 316.
- Corrosion resistanceExcellent
- Resists chloride pitting and crevice attack far better than 304 (pitting resistance number about 24-26 versus 18-19), plus sulfuric, phosphoric and acetic acids and marine air. Still cracks in hot chlorides under stress and pits in stagnant warm seawater; 2205 or titanium beyond that.
316 is the second most common stainless and the one specified when 304 pits. Its 2-3% molybdenum, with slightly more nickel, roughly doubles the resistance to chloride pitting and crevice corrosion, which is why it is the default for marine hardware, coastal architecture, chemical and pharmaceutical process equipment, food plants that wash down with chlorinated cleaners, and medical devices. 316L, with carbon held to 0.03%, is the version for welded construction and for electropolished sanitary parts; most stock is dual-certified 316/316L.
Mechanically it is 304: 515-620 MPa (75-90 ksi) tensile annealed, 40-55% elongation, not hardenable by heat treatment, strengthened only by cold work. It is a little less formable than 304 and a little slower to machine (about 36-45% of B1112), and it stays closer to non-magnetic after cold work because the extra nickel stabilizes the austenite. It welds exactly as 304 does, with 316L filler.
It is not immune to chlorides. Warm seawater in crevices, hot brines and chloride solutions under stress above about 60 °C (140 °F) still attack it; those jobs go to 2205 duplex, 6% Mo super-austenitics or titanium. In plain indoor, fresh-water and food service 316 buys nothing over 304 except a 15-30% higher price.
Heat treatment
Not hardenable by heat treatment; strength comes only from cold work. Solution anneal at 1040-1120 °C (1900-2050 °F) and water quench. Avoid holding 316 at 425-870 °C (800-1600 °F) where carbides sensitize the grain boundaries; 316L tolerates that range. Low-temperature stress relief at 350-400 °C (660-750 °F) is used on machined parts.
Tempers and conditions
- Annealed (2B, 2D, BA, #4 finishes on sheet)
- 1/4 hard to full hard strip (ASTM A666)
- Cold-drawn bar
- Hot-rolled, annealed and pickled plate (HRAP)
Stock forms
- Sheet and coil (2B, #4, BA)
- Plate
- Round, square, hex and flat bar
- Pipe (ASTM A312) and tube (ASTM A269, A270 sanitary)
- Angle and structural shapes
- Wire and fasteners (A4)
- Castings as CF8M (316) and CF3M (316L)
Relative cost
Tier 3 of 5. About 1.2-1.4x 304 per pound, driven by the molybdenum and extra nickel. Stocked nearly as widely as 304 in sheet, plate, bar and tube; premiums grow on thick plate and large-diameter bar.
Typical applications
- Marine hardware, deck fittings and boat rails
- Chemical, pharmaceutical and semiconductor process equipment
- Sanitary tubing, valves and tanks for food and beverage
- Surgical instruments and implants (316LVM)
- Coastal architecture and railings
- Heat exchangers and condensers
- Pulp and paper, and wastewater equipment
- Laser-cut and 3D-printed parts in corrosive service
Process compatibility
How 316 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Machining | FairFair | A shade slower than 304; sharp carbide, steady feed, flood coolant. Fine for fittings and manifolds in low volume. |
| Laser Cutting | ExcellentExcellent | Cuts like 304 with nitrogen assist for a clean, weldable edge; fiber lasers handle sheet to about 25 mm (1"). |
| Waterjet Cutting | ExcellentExcellent | No heat-affected zone or heat tint; the choice for thick plate and sensitization-sensitive parts. |
| Press Brake Forming | GoodGood | Bend at 1-2t inside radius with 2-4 degrees of over-bend for springback; a touch stiffer than 304. |
| Deep Drawing | GoodGood | Draws well but with less reach than 304; add an intermediate anneal on deep shells. |
| Welding | ExcellentExcellent | 316L filler by TIG or MIG; 316L base metal for heavy sections; argon back-purge and post-weld pickling or electropolishing for chloride service. Can 316 stainless steel be welded? |
| TIG Welding | ExcellentExcellent | The process for sanitary tube and thin sheet; orbital TIG on tubing gives the smooth, purged root sanitary specs require. |
| Passivation | ExcellentExcellent | ASTM A967 or AMS 2700 citric or nitric after machining; standard on marine, food and medical parts. |
| Electropolishing | ExcellentExcellent | The classic electropolished grade: 316L gives the smoothest, brightest, most passive surface for sanitary, pharmaceutical and semiconductor work. |
| Metal 3D Printing | ExcellentExcellent | 316L is the most printed stainless: laser powder bed parts reach wrought-like strength and are stress relieved or annealed after the build. |
| Investment Casting | GoodGood | Cast as CF8M or CF3M for valve bodies, pump parts and marine fittings; castings run with a little ferrite for weldability. |
| Heat Treating | Not recommendedNot recommended | Cannot be hardened; annealing only. For a hard corrosion-resistant part use 17-4 PH (overaged) or 440C, accepting less chloride resistance. |
| Anodizing | Not recommendedNot recommended | Anodizing is an aluminum process; stainless does not grow a useful anodic film. For colour, use PVD coating, black oxide or electrochemical colouring; for corrosion, passivate or electropolish. |
| Hot-Dip Galvanizing | Not recommendedNot recommended | Zinc does not bond to the passive oxide and adds nothing; zinc contact on hot stainless can cause liquid-metal cracking. |
Compare 316
Design and sourcing tips
- Write "316/316L dual certified per ASTM A240 (or A276 for bar)" whenever the part is welded; it costs nothing and removes the sensitization argument.
- Specify 316L, not 316, for anything to be electropolished or used in sanitary or pharmaceutical service, and add the Ra target after EP.
- Do not pay for 316 indoors or in fresh water; specify it for chlorides, coastal air, chlorinated washdown and acids, where it earns the premium.
- For hot chlorides under stress (above about 60 °C / 140 °F), 316 will crack: move to 2205 duplex or titanium instead of adding wall thickness.
- Call passivation per ASTM A967 after machining and heat-tint removal after welding; a heat-tinted 316 weld pits before the base metal does.
- Stainless fasteners gall: specify anti-seize or a dissimilar pairing (316 bolt in a 304 or bronze nut) on threaded joints that are assembled more than once.
Frequently asked questions
- Is 316 stainless steel magnetic?
- No, as annealed. It is austenitic and stays nearly non-magnetic even after cold work, because its higher nickel content suppresses the strain-induced martensite that makes cold-worked 304 slightly magnetic. Cast CF8M contains some ferrite and is faintly magnetic.
- What is the difference between 316 and 316L?
- Carbon: 316 allows up to 0.08%, 316L up to 0.03%. Low carbon keeps chromium carbides from forming in weld heat-affected zones, so 316L welds hold their corrosion resistance without a post-weld anneal, and it electropolishes more evenly. 316L is about 15 MPa (2 ksi) weaker on paper. Most stock is dual-certified.
- Is 316 stainless good for saltwater?
- Good, with limits. It handles marine air, splash and flowing seawater far better than 304, which is why it is the standard boat and dock hardware. Stagnant warm seawater in crevices (under washers, in threads, inside sealed tubes) can still pit it, and hot brines under stress can crack it. For immersed seawater equipment use 2205, a 6% Mo super-austenitic or titanium.
- Can 316 stainless be hardened?
- Not by heat treatment. Like 304, it strengthens only by cold work; spring-temper strip reaches about 1200 MPa (175 ksi). A hard, corrosion-resistant part is usually 17-4 PH or 440C, both of which give up some chloride resistance compared with 316.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM A240 and ASTM A276 (property minimums by product form)
- AMS 5524 and AMS 5648 (316); AMS 5507 and AMS 5653 (316L); ASTM F138 (316LVM)
- ASM Handbook, Volume 1 and Volume 13B (corrosion of stainless steels)
- Nickel Institute design guides and producer data sheets (Outokumpu, NAS, ATI)
