The austenitic workhorse for marine, medical, and chemical-process environments. The 2–3% molybdenum addition over 304 gives 316L its defining advantage — pitting resistance in chloride-rich environments like seawater, body fluids, and de-icing salts. The "L" low-carbon variant prevents sensitization during welding, essential for fabricated assemblies.
The choice between 304 and 316L is almost entirely about chloride exposure. In clean, dry, indoor environments, 304 performs identically to 316L at 70% of the cost. But introduce seawater, sweat, chlorinated cleaning agents, food brines, or de-icing salt runoff, and 304 pits and crevice-corrodes within weeks while 316L shrugs it off. The 2–3% molybdenum in 316L changes the passive oxide chemistry enough that localized corrosion initiation requires much higher chloride concentrations.
The "L" designation (316L vs 316) means carbon is kept below 0.03% — crucial for welded assemblies. Standard 316 with 0.08% carbon is prone to sensitization: during welding, chromium carbides precipitate at grain boundaries, depleting the adjacent metal of chromium and creating corrosion pathways. For machined monolithic parts that won't be welded, both 316 and 316L perform identically. But the industry has standardized on 316L because the price premium is minimal and it removes a failure mode.
316L is tough on tooling. It work-hardens rapidly if feeds are too light, generates built-up edge at moderate speeds, and has only 45% the machinability of free-machining steel. Expect 30–50% higher machining cost per pound than 304, and 2–3× vs. carbon steel. Budget for it — specifying 316L for parts that see no chlorides is one of the most common procurement-engineering disconnects we see.
| Element | Min % | Max % | Role |
|---|---|---|---|
| Chromium (Cr) | 16.0 | 18.0 | Passivation layer formation |
| Nickel (Ni) | 10.0 | 14.0 | Austenite stabilization |
| Molybdenum (Mo) | 2.0 | 3.0 | Pitting & crevice corrosion resistance |
| Carbon (C) | — | 0.030 | Low-C prevents sensitization |
| Manganese (Mn) | — | 2.00 | Deoxidizer, austenite former |
| Silicon (Si) | — | 0.75 | Deoxidizer |
| Phosphorus (P) | — | 0.045 | Impurity |
| Sulfur (S) | — | 0.030 | Impurity |
| Nitrogen (N) | — | 0.10 | Strengthening, austenite stabilizer |
| Iron (Fe) | balance | Matrix | |
| Property | Metric | Imperial | Test method |
|---|---|---|---|
| Ultimate tensile strength | 515 MPa min | 75,000 psi | ASTM E8 |
| Yield strength (0.2%) | 205 MPa min | 30,000 psi | ASTM E8 |
| Elongation at break | 40% min | 40% | ASTM E8 |
| Hardness (max, annealed) | 217 HB / 95 HRB | — | ASTM E10/E18 |
| Modulus of elasticity | 193 GPa | 28×10⁶ psi | ASTM E111 |
| Density | 8.00 g/cm³ | 0.289 lb/in³ | — |
| Thermal conductivity | 16.3 W/m·K | — | Low — retains heat during cutting |
| PREN (pitting resistance) | 25–28 | Cr + 3.3×Mo + 16×N | |
| Magnetic | No (austenitic) | May become slightly magnetic after cold work | |
| Max service temperature | ~870°C | ~1600°F | Oxidation threshold |
Rigid setups, sharp tools, flood coolant. The cardinal rule: don't let the tool dwell. Continuous feed with adequate depth prevents work-hardening. Carbide grades: coated (TiAlN/AlTiN) for most operations, cermet for finishing.
| Operation | Surface speed (m/min) | Feed per tooth (mm) | Depth of cut | Tool |
|---|---|---|---|---|
| Face milling (rough) | 120–180 | 0.10–0.20 | 1.5–3 mm | Coated carbide, tough grade |
| Face milling (finish) | 150–220 | 0.08–0.12 | 0.2–0.5 mm | Coated carbide or cermet |
| End milling (rough) | 80–130 | 0.05–0.12 | 1–1.5× dia | Solid carbide, variable helix |
| End milling (finish) | 100–160 | 0.03–0.08 | 0.1–0.3 mm | Fine-grain carbide, 4-flute |
| Drilling | 20–35 | 0.08–0.20/rev | — | Cobalt HSS or carbide, peck cycle |
| Tapping | 4–8 | — | — | Cobalt spiral-flute, use paste lubricant |
| Turning (rough) | 120–180 | 0.20–0.40/rev | 2–4 mm | Coated carbide CNMG, positive rake |
| Turning (finish) | 150–240 | 0.08–0.20/rev | 0.3–0.8 mm | Cermet or coated carbide |
Surgical tools, bone screws (short-term), orthodontic components. ISO 5832-1 for implant grade with tighter inclusion limits.
Sailboat fittings, underwater sensors, offshore platform components. Pairs with 316L fasteners to avoid galvanic issues.
Valves, manifolds, mixing equipment. 3-A Sanitary Standards compliance, electropolished for CIP/SIP cleanability.
Filling nozzles, mixing impellers, bioreactor internals. ASME BPE compliance for Ra specifications.
Valves, pump shafts, heat exchanger components for dilute acid and chloride service.
Ultra-high-purity gas and chemical delivery manifolds. Electropolished, argon-purged packaging.
| Property | 304 | 316L | Notes |
|---|---|---|---|
| Chromium | 18–20% | 16–18% | Similar passivation |
| Nickel | 8–10.5% | 10–14% | 316L more stable austenite |
| Molybdenum | — | 2–3% | The key difference |
| PREN | 17–19 | 25–28 | Pitting resistance index |
| Chloride resistance | Poor above 200 ppm | Good to 1000+ ppm | Marine difference |
| Typical cost | Baseline | 1.4–1.6× 304 | Mo drives premium |
| Machinability | Similar | Slightly worse | Both tough to machine |
| Use indoors, dry | Yes — save money | Overkill | Specify 304 |
| Use outdoors, marine, medical | Will fail | Yes | Specify 316L |
Machining embeds iron particles into the surface and disturbs the passive chromium oxide layer. Without passivation (ASTM A967 citric or nitric), 316L can show rust within days of exposure to humidity. We passivate 316L parts by default unless you specify otherwise.
Not because the alloy itself is that different (it's actually similar machinability), but because tolerances are usually tighter, surface finishes higher, and passivation adds a step. The cost gap is usually in the finishing operations, not the cutting.
Smaller radii force small-diameter tooling that deflects under 316L's cutting forces. If your design has sharp internal corners, expect either radius compromises or EDM operations — both add cost. Design around this early.
Only if the part will be welded after machining, or subjected to sustained temperatures above 425°C (sensitization range). For solid-machined, non-welded parts used below that temperature, regular 316 and 316L are functionally identical. Industry default is 316L anyway — don't spec 316 unless you have a reason.
If your application is implant-grade, specify ISO 5832-1 or ASTM F138 — these require tighter non-metallic inclusion content than standard ASTM A276 bar. Source material cost ~1.3× standard 316L. Required for FDA-cleared medical devices.
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