Stainless Steel 316
Chemical Composition
Section titled “Chemical Composition”Stainless Steel 316 is an austenitic chromium-nickel-molybdenum steel with the following chemical composition (% by mass):
| Element | % Min | % Max |
|---|---|---|
| Carbon (C) | — | 0.08 |
| Manganese (Mn) | — | 2.00 |
| Silicon (Si) | — | 1.00 |
| Phosphorus (P) | — | 0.045 |
| Sulfur (S) | — | 0.030 |
| Chromium (Cr) | 16.0 | 18.0 |
| Nickel (Ni) | 10.0 | 14.0 |
| Molybdenum (Mo) | 2.00 | 3.00 |
| Iron (Fe) | Balance | Balance |
The addition of molybdenum notably improves resistance to pitting corrosion and in chloride environments. The low-carbon version, 316L (C ≤ 0.03%), is especially suitable for applications with welding or risk of sensitization.
Equivalent Designations
Section titled “Equivalent Designations”The main equivalent designations for stainless steel 316 are:
| Standard | Designation |
|---|---|
| UNS | S31600 |
| EN | 1.4401 |
| AISI/SAE | 316 |
| DIN | X5CrNiMo17-12-2 |
| BS | 316S31 |
| JIS | SUS 316 |
For the low-carbon version, the EN designation is 1.4404 and the UNS is S31603.
Mechanical Properties
Section titled “Mechanical Properties”Mechanical properties vary according to heat treatment condition. Typical values for material in annealed condition are shown below:
| Property | SI Unit | Value (annealed) | Imperial Unit |
|---|---|---|---|
| Yield strength (0.2% offset) | MPa | 205 min | 30 ksi min |
| Tensile strength | MPa | 515 – 690 | 75 – 100 ksi |
| Elongation in 50 mm | % | 40 | — |
| Rockwell B hardness | HRB | 79 max | — |
| Brinell hardness | HB | 217 max | — |
With moderate cold working, yield strengths above 480 MPa and tensile strengths near 620 MPa can be achieved, but with significant reduction in ductility.
Physical and Thermal Properties
Section titled “Physical and Thermal Properties”The density of 316 steel is approximately 8.0 Mg/m³ (500 lb/ft³). Other notable properties are:
| Property | SI Value | Imperial Value |
|---|---|---|
| Density at 20 °C | 7.99 g/cm³ | 0.288 lb/in³ |
| Modulus of elasticity (Young) | 193 GPa | 28 × 10⁶ psi |
| Shear modulus | 77 GPa | 11.2 × 10⁶ psi |
| Poisson’s ratio | 0.27 | 0.27 |
| Specific heat | 500 J/(kg·K) | 0.12 BTU/(lb·°F) |
| Thermal conductivity at 100 °C | 16.2 W/(m·K) | 112 BTU·in/(h·ft²·°F) |
| Coefficient of thermal expansion (20‑100 °C) | 16.0 × 10⁻⁶ /K | 8.9 × 10⁻⁶ /°F |
| Melting point | 1375 – 1400 °C | 2500 – 2550 °F |
| Maximum service temperature (air) | 870 °C | 1600 °F |
| Electrical resistivity at 20 °C | 74 × 10⁻⁸ Ω·m | 29.1 Ω·circ‑mil/ft |
The alloy is non-magnetic in the annealed condition and may exhibit some magnetic response after cold working.
Corrosion Resistance
Section titled “Corrosion Resistance”316 steel offers superior corrosion resistance to 304, especially in chloride-containing environments, thanks to molybdenum. Its characteristics include:
- Resistance to pitting and crevice corrosion in seawater and moderate chloride environments.
- Resistance to reducing acids (sulfuric, phosphoric, acetic) at moderate concentrations and temperatures.
- Excellent performance in urban and rural atmospheres, as well as in mild industrial environments.
- Not suitable for prolonged exposure to hot concentrated sulfuric acid, hydrochloric acid, or chlorides at elevated temperatures where stress corrosion cracking may occur.
The low-carbon version (316L) minimizes chromium carbide precipitation during welding, maintaining intergranular corrosion resistance.
Heat Treatments
Section titled “Heat Treatments”316 is not hardenable by heat treatment. Most properties are obtained by annealing and subsequent rapid cooling.
| Treatment | Temperature | Duration | Cooling |
|---|---|---|---|
| Solution annealing | 1010 – 1120 °C | 15 – 30 min per 25 mm thickness | Water or forced air |
| Stress relief | 400 – 600 °C | 1 – 2 h | Air |
Slow cooling between 550 °C and 850 °C can cause precipitation of undesirable phases and loss of corrosion resistance. Welded parts with low carbon (316L) do not require post-weld annealing if thickness does not exceed 6 mm.
Industrial Applications
Section titled “Industrial Applications”Stainless steel 316 is used in a wide variety of sectors:
- Chemical and petrochemical industry: pressure vessels, heat exchangers, piping for corrosive fluids.
- Food industry: processing equipment, fermentation tanks, surfaces in contact with acidic or salty foods.
- Pharmaceutical and medical: autoclaves, surgical instruments, temporary implants.
- Marine and coastal: components exposed to saltwater splashes, nautical fittings, handrails in coastal areas.
- Water treatment: drinking water pipes, desalination plants, wastewater treatment plants.
- Architecture: cladding, facades, and structural elements in urban and coastal environments.
Comparison with Similar Materials
Section titled “Comparison with Similar Materials”Below, 316 steel is compared with other austenitic and duplex stainless steels:
| Material | Cr | Ni | Mo | Chloride resistance (PREN)* | Relative cost |
|---|---|---|---|---|---|
| AISI 304 | 18‑20 | 8‑10.5 | — | 18‑20 | 1 |
| AISI 316 | 16‑18 | 10‑14 | 2‑3 | 24‑26 | 1.3 |
| AISI 316L | 16‑18 | 10‑14 | 2‑3 | 24‑26 | 1.4 |
| Duplex 2205 | 22‑23 | 4.5‑6.5 | 3‑3.5 | 34‑36 | 1.8 |
*PREN = %Cr + 3.3 × %Mo + 16 × %N (higher PREN indicates greater pitting resistance).
Compared to 304, 316 practically doubles pitting corrosion resistance and extends the range of use in marine environments. Duplex grades (such as 2205) offer higher mechanical strength and better performance in chlorides, although at a higher cost than 316.
Available Formats
Section titled “Available Formats”Stainless steel 316 is supplied in the following commercial formats:
- Sheet and strip: thicknesses from 0.5 to 50 mm, widths up to 2000 mm.
- Bars and profiles: round, square, hexagonal, and angles from 3 mm to 300 mm.
- Seamless and welded tubes: diameters from 6 mm to 610 mm.
- Wire and electrodes: for welding and spring or mesh applications.
- Forgings and castings: according to ASTM A743/A744 specification.
It is also available in surface finishes ranging from hot rolled (No. 1) to bright polished (No. 8), including satin and ground finishes for decorative applications.
Manufacturing Notes
Section titled “Manufacturing Notes”- Machining: 316 has machinability of about 45% compared to carbon steel. Carbide or cobalt high-speed steel tools with abundant cooling are recommended.
- Welding: Supports TIG, MIG, submerged arc, and resistance welding. 316L or 309Mo fillers are preferred to reduce risk of intergranular corrosion.
- Cold forming: Possesses excellent ductility, allowing deep drawing, bending, and profiling without heating. It work-hardens at a moderate rate.
- Cutting: Supports plasma, laser, and waterjet cutting. For thin thicknesses, it can be cut with shears.
The surface should always be cleaned after fabrication to remove thermal oxides and ferritic contamination that could initiate corrosion.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the density of stainless steel 316?
Section titled “What is the density of stainless steel 316?”The density is approximately 8.0 g/cm³, which is equivalent to about 500 lb/ft³ in imperial units.
What is the difference between 316 and 316L?
Section titled “What is the difference between 316 and 316L?”316L has a maximum carbon content of 0.03%, compared to 0.08% for 316. This reduces the risk of intergranular corrosion after welding or heat treatments, while the rest of the properties remain practically identical.
What is the maximum working temperature for 316?
Section titled “What is the maximum working temperature for 316?”In continuous service in air, the maximum recommended temperature is 870 °C. For intermittent exposures, it can reach up to 925 °C.
What is the minimum tensile strength in the annealed condition?
Section titled “What is the minimum tensile strength in the annealed condition?”The minimum tensile strength is 515 MPa (75 ksi). In the cold-worked condition, it can exceed 620 MPa.
Is 316 magnetic?
Section titled “Is 316 magnetic?”No, it is essentially non-magnetic in the annealed condition. After cold working, it may show slight magnetism due to partial transformation to martensite.
Can 316 steel be used in seawater?
Section titled “Can 316 steel be used in seawater?”Yes, it offers good corrosion resistance for short-term immersion or saltwater splashes, but it is not suitable for permanent immersion at high temperature or in conditions of very low oxygen renewal, where pitting may occur. For such applications, superduplex steels are recommended.
References
Section titled “References”- azom.com: https://www.azom.com/properties.aspx?ArticleID=863
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/stainless-steel-classifications-d_368.html
- steelnumber.com: https://www.steelnumber.com/en/steel_alloy_composition_eu.php?name_id=2132