Among the metal alloys processed by Direct Metal Laser Sintering, 316L stainless steel occupies a distinct position: it is neither the strongest nor the lightest, but it is the most versatile. Its combination of austenitic structure, molybdenum-enhanced corrosion resistance, and established biocompatibility certification pathways makes it the specification of choice across medical devices, food processing equipment, chemical plant, and marine hardware.
Understanding what DMLS does to 316L — and what post-processing options are available — is essential for specifying it correctly for regulated applications.
Why 316L Outperforms 304 in Corrosive Environments
304 stainless steel is 18% Cr / 8% Ni. 316L adds 2–3% molybdenum. That single addition is decisive: molybdenum disrupts the pitting corrosion mechanism driven by chloride ions, raising the Critical Pitting Temperature (CPT) from approximately 15°C for 304 to above 35°C for 316L in seawater conditions. In practice this means 316L resists crevice corrosion in chlorinated water, mild acids, and marine spray environments where 304 would require passivation schedules and periodic replacement.
The "L" designation indicates low carbon content — maximum 0.03% C — which prevents chromium carbide precipitation at grain boundaries during welding and thermal processing. For DMLS, where each layer undergoes repeated heat cycles as new layers are deposited above, the low carbon content is critical to maintaining intergranular corrosion resistance in the as-built state.
DMLS 316L Mechanical Properties
| Property | DMLS As-Built | DMLS + Annealed | Wrought 316L |
|---|---|---|---|
| UTS | 640 MPa | 560 MPa | 515 MPa |
| 0.2% Proof Strength | 530 MPa | 420 MPa | 205 MPa |
| Elongation at Break | 25–35% | 40–50% | 40%+ |
| Hardness | 88 HRB | 79 HRB | 79 HRB |
| Density | 7.8–7.9 g/cm³ | 7.9 g/cm³ | 7.98 g/cm³ |
DMLS 316L as-built is noticeably stronger than wrought due to the fine cellular dendritic microstructure created by rapid solidification. Yield strength is more than double the wrought value — a meaningful advantage for parts carrying compressive or tensile loads. Annealing sacrifices some of this strength gain in exchange for improved ductility and stress relief, bringing properties closer to the well-characterised wrought baseline that regulatory submissions reference.
Corrosion Behaviour of DMLS 316L
Multiple published studies comparing DMLS and wrought 316L in 3.5% NaCl solution (simulated seawater) show that DMLS 316L in the as-built condition has a slightly lower pitting potential than wrought — attributed to microsegregation at solidification cell boundaries and sub-surface porosity. However, after solution annealing (1,050°C / 30 min, water quench) the pitting potential of DMLS 316L converges with wrought within measurement uncertainty.
For applications requiring full corrosion performance equivalence to wrought — marine hardware, chemical process valves, pharmaceutical equipment — solution anneal and passivation should be specified.
Biocompatibility and Medical Device Applications
316L stainless steel has a long history of use in medical implants (surgical instruments, orthopaedic implants, dental tools). DMLS 316L can be qualified for Class I and Class II medical device applications under ISO 10993 biocompatibility testing. The qualification pathway requires:
- Powder chemistry certification confirming composition within ASTM F138 (implant grade) or ASTM A276 requirements
- Full solution anneal to homogenise the microstructure and eliminate solidification segregation
- Passivation per ASTM A967 (nitric or citric acid bath) to maximise the Cr₂O₃ passive layer
- Electropolishing for implantable devices — reduces Ra to ≤0.4 µm and removes the surface-enriched iron layer
- ISO 10993-1 cytotoxicity, sensitisation, and pyrogenicity testing for the specific application
Layer X holds ISO 13485 certification for medical component production. Our quality system supports full material traceability from powder certificate through machining, heat treatment, and surface finishing records for regulatory submissions.
Post-Processing Options
Solution Annealing
1,050–1,100°C / 30–60 min in inert atmosphere, water quench. Homogenises microstructure, relieves residual stress, maximises ductility and corrosion resistance. Standard specification for medical, food contact, and marine applications.
Passivation
Nitric or citric acid bath per ASTM A967. Removes free iron from the surface and thickens the chromium oxide passive layer. Minimum 24-hour passive film stabilisation before service. Mandatory for food-contact parts and recommended for all corrosive-environment applications.
Electropolishing
Electrochemical material removal in phosphoric/sulfuric acid bath. Removes 5–30 µm of surface material, preferentially attacking peaks over valleys. Reduces Ra from 4–8 µm (as-built) to 0.1–0.4 µm. Eliminates crevice-prone surface topology. Standard finishing for pharmaceutical, dairy, and semiconductor-grade components.
Media Blasting and Tumbling
Glass bead or alumina blasting removes residual powder and gives a uniform matte finish without significantly changing Ra. Vibratory tumbling achieves Ra 1–3 µm — suitable for general industrial parts without regulatory surface requirements.
Industry Applications
Medical Devices
Surgical instrument handles, laparoscopic component bodies, orthopaedic cutting guides, sterilisation trays, custom implant trials. DMLS enables patient-specific geometry that machined instruments cannot approach. Electropolished DMLS 316L passes standard autoclave and gamma sterilisation without degradation.
Food and Beverage Processing
Impeller housings, valve bodies, conveyor guide rails, mixing chamber liners. 316L's chloride resistance handles CIP (Clean-In-Place) caustic and acidic wash cycles. Electropolished surfaces meet EU 10/2011 and US FDA 21 CFR food contact standards.
Chemical Process and Pharmaceutical
Manifolds with complex internal flow paths, heat exchanger fins, micro-reactor channels. DMLS produces internal geometries that fabricated sheet metal cannot achieve. The ASME BPE (Bioprocessing Equipment) standard specifies Ra ≤ 0.4 µm for product-contact surfaces — achievable with electropolishing on DMLS 316L.
Marine and Offshore
Hardware, brackets, and fastener systems in chloride-rich environments. After solution anneal and passivation, DMLS 316L outperforms cast 316 in pitting resistance due to the finer grain structure.
Layer X produces 316L under ISO 9001 and ISO 13485 with documented heat treatment and surface finishing records. Contact us to discuss your application requirements, or upload your part files for a DMLS 316L quote with optional post-processing specifications.