Overview
Type 316 is the second most common austenitic stainless steel, with molybdenum added (2-3%) to improve chloride and reducing-acid corrosion resistance. It is the grade specified for marine, coastal, chemical processing, and pharmaceutical applications. 316L is the low-carbon variant for welded construction.
Mechanical Properties
| Property | 316 (Annealed) | 316L (Low Carbon) |
|---|---|---|
| Density | 8,000 kg/m³ | 8,000 kg/m³ |
| Yield Strength (0.2%) | 205 MPa | 170 MPa |
| Ultimate Tensile | 515 MPa | 485 MPa |
| Elongation | 40% | 40% |
| Hardness | 180 BHN max | 180 BHN max |
| Young's Modulus | 193 GPa | 193 GPa |
Corrosion Resistance — Molybdenum Advantage
316's 2.5% molybdenum provides significantly better resistance than 304 to:
- Chloride pitting/crevice corrosion: PREN ≈ 25 (vs ~18 for 304)
- Seawater and salt-laden coastal air
- Sulfuric and phosphoric acids
- Sulfurous atmospheres (pollution, pulp/paper)
- Many organic and fatty acids (food processing)
- Pharmaceutical and clean-room environments
Limitations
Despite better performance than 304, 316 still has limitations:
- Chloride SCC: Still susceptible above ~60°C in chloride environments
- Continuous service above 870°C: Sigma phase embrittlement possible
- Hydrochloric acid: Attacked even at dilute concentrations
- Cost: ~30-50% more expensive than 304
Thermal Properties
| Property | Value |
|---|---|
| Melting Range | 1375-1400°C |
| Thermal Conductivity (100°C) | 16 W/m·K |
| Specific Heat | 500 J/kg·K |
| Coefficient of Thermal Expansion | 16.5 × 10⁻⁶ /°C |
Applications
- Marine hardware (boat fittings, dock hardware, propeller shafts)
- Coastal architectural (handrails, cladding, fasteners)
- Chemical process equipment (pumps, valves, heat exchangers)
- Pharmaceutical manufacturing (clean, non-contaminating)
- Medical implants and devices (surgical instruments, orthopedic)
- Food processing (salty/acidic products, soy sauce, brine)
- Pulp and paper (bleach plants)
- Photographic and textile processing
Common 316 Variants
| Grade | Difference | Application |
|---|---|---|
| 316L | Low carbon (<0.03%) | Welded construction |
| 316H | High carbon (0.04-0.10%) | High temperature (>500°C) |
| 316Ti | Titanium-stabilized | High temperature, welded |
| 316N | Nitrogen added | Higher strength |
| 316LVM | Vacuum melted | Medical implants |
Fabrication Notes
- Weld with 316L filler (or 318 with higher Mo)
- Slightly higher springback than 304 in forming
- Slightly more difficult to machine than 304 due to work-hardening
- Passivate after machining/welding to restore corrosion resistance
- Non-magnetic in annealed condition
Summary
Type 316/316L (density 8000 kg/m³, 2.5% Mo) is the marine and chemical-grade stainless steel with PREN ~25. It provides vastly better chloride and reducing acid resistance than 304. Use 316L for welded construction. Standard for coastal, marine, chemical, pharmaceutical, and food processing with salt/brine. The 30-50% cost premium over 304 is justified by extended service life in corrosive environments.