Titanium vs Stainless Steel: Ti-6Al-4V vs 316L for Aerospace and Medical Parts

For load-bearing permanent implants, ASTM F136-26 (Ti-6Al-4V ELI, UNS R56401) is the specification you write on the drawing. ASTM F138 wrought 316L bar and wire (UNS S31673) covers short-term implants and surgical instruments where cost matters more than fatigue life. For aerospace bar, wire, forgings, and rings, SAE AMS4928X covers Ti-6Al-4V annealed and SAE AMS5653K covers 316L in solution heat treated condition. Both aerospace callouts specify alloy, revision, product form, and condition together, not the bare grade name.

This article covers CNC-grade bar, wire, forging stock, and small-diameter rings up to about 254 mm (10 in.). It does not cover plate forming, additive manufacturing, casting, or sheet-metal work.

1. Is Ti-6Al-4V stronger than 316L? A direct answer

Depends on which strength you mean.

On absolute tensile strength, Ti-6Al-4V wins for CNC bar stock. SAE AMS4928X Table 2 requires ultimate tensile strength of at least 931 MPa (135 ksi) for annealed bar up to 2.000 in (50.80 mm) diameter, with a minimum 0.2% yield of 862 MPa (125 ksi). SAE AMS5653K Table 2 requires only 482 MPa (70 ksi) UTS min and 172 MPa (25 ksi) 0.2% yield min for 316L bar and forging in solution heat treated condition above 0.50 in (12.7 mm). Ti-6Al-4V bar is roughly 1.9x stronger on UTS and about 5x on yield at these minimum specification values, and the way you read yield strength vs tensile strength for CNC part selection determines whether that gap matters for your design.

On strength-to-weight, the gap widens. Ti-6Al-4V density runs about 4.43 g/cm³ against 7.99 g/cm³ for 316L. That gives Ti-6Al-4V a specific UTS around 210 kN·m/kg versus 60 kN·m/kg for 316L, roughly a factor of 3.5 on spec minimums. Commercial 316L bar leaves mills at yield values well above the AMS5653K minimum, so the real-world strength-to-weight advantage for Ti-6Al-4V lands closer to two.

316L wins on stiffness. Modulus of elasticity sits near 195 GPa for annealed 316L against 110 to 114 GPa for annealed Ti-6Al-4V. If your part is deflection-limited under load, 316L wins regardless of specific strength. For the same wall thickness and geometry, a 316L bracket deflects less than a Ti-6Al-4V bracket at the same load.

316L can also match or exceed Ti-6Al-4V on absolute strength in heavily cold-drawn fine wire per ASTM F138-19, but at gauge sizes below the CNC bar range.

2. Ti-6Al-4V vs 316L: property comparison anchored to standards

The table below pulls each row from the standard’s own text. Chemistry and mechanical values are specification minimums, not vendor catalog numbers, and each is tied to a specific size and condition. Density and modulus at the bottom are published engineering reference values because neither standard mandates them.

Ti-6Al-4V per AMS4928X vs 316L per AMS5653K, CNC bar and forging basis

UNS relationship	Similar to UNS R56400	Similar to UNS S31603
Delivery condition	Annealed	Solution heat treated
Key alloy content (wt%)	Al 5.50 to 6.75, V 3.50 to 4.50	Cr 16.00 to 18.00, Ni 10.00 to 14.00, Mo 2.00 to 3.00
Carbon max (wt%)	0.08	0.030
Applicable size for Table 2	Bar ≤2.000 in (50.80 mm) diameter	Bar and forging above 0.50 in (12.7 mm)
Ultimate tensile strength min	931 MPa (135 ksi)	482 MPa (70 ksi)
0.2% yield strength min	862 MPa (125 ksi)	172 MPa (25 ksi)
Elongation min (longitudinal)	10%	40% hot-finished / 30% cold-finished
Reduction of area min (longitudinal)	25%	50% hot-finished / 40% cold-finished
Hardness	Not specified in AMS4928X	140 to 255 HBW for bar ≤2.000 in (50.80 mm)
Density (published reference)	4.43 g/cm³	7.99 g/cm³
Elastic modulus (published reference)	110 to 114 GPa	~195 GPa

Three lines matter for how you read this table.

The alloy identity clause reads “similar to UNS R56400” and “similar to UNS S31603” in each standard’s title. That leaves room for chemistry inside the AMS envelope but outside a supplier’s stated UNS chemistry, so a material certificate quoting only the UNS number is not proof of AMS compliance.

AMS4928X gives four size tiers for tensile properties. The table shows the ≤2.000 in bar tier for direct comparison against the 316L specification. Larger Ti-6Al-4V diameters drop to 896 MPa UTS min and 827 MPa YS min with the same 10% elongation floor. The 316L spec applies its Table 2 values to any bar or forging over 0.50 in diameter, without size tiers.

Condition control differs. AMS4928X leaves annealing temperature and time to the producer under the annealed condition label, while AMS5653K requires solution heat treated delivery but does not specify a temperature. If a drawing requires a specific solution temperature or annealing cycle, the RFQ must call it out separately.

The table does not cover corrosion or microstructure control. AMS5653K requires an intergranular attack test on sensitized material per ASTM A262 Practice A or E. AMS4928X requires alpha case limits and microstructure control under its own acceptance clauses. Neither test is a mechanical property, but both are acceptance conditions on the material certificate.

For a broader alloy-family comparison against 6061, 7075, 4140, brass C360, and other CNC-grade materials, see the metal strength chart for CNC materials and the materials and properties reference.

3. Aerospace grade: AMS 4928 titanium vs AMS 5653 stainless steel

Aerospace bar for a Ti-6Al-4V or 316L flight part is not described by the alloy name alone. The correct procurement string on a drawing or PO reads alloy + specification + revision + product form + condition. For Ti-6Al-4V annealed bar per the current revision:

Ti-6Al-4V per SAE AMS4928X, annealed, bar

For 316L in the solution-heat-treated condition:

316L per SAE AMS5653K, solution heat treated, bar

Drop any element and the material certificate no longer proves compliance. Revision letters carry real content. AMS4928X added vacuum arc skull melting as an initial melting route requiring reporting, revised the lot definition, and updated exception handling and ordering information. AMS5653K added strain-rate control for tensile testing, added bar finish requirements, and updated exception clauses. Under AMS5653K a supplier can also ship inventory manufactured to the immediately previous revision until existing stock is consumed. A PO that says only “AMS5653” does not force the K revision, so it must be written as AMS5653K explicitly.

Both standards note the alloy is “similar to” a UNS designation, not equivalent: UNS R56400 for AMS4928X and UNS S31603 for AMS5653K. That distinction has cost implications. A vendor certificate showing only “UNS R56400” or “UNS S31603” chemistry can fall inside the UNS envelope but outside the AMS envelope on iron, oxygen, or other trace-element limits.

Two AMS-specific rules on 316L bar catch buyers who assume material is fungible. AMS5653K states “Bars shall not be cut from plate.” A supplier who reduces sheet or plate stock to bar-shaped strips does not deliver AMS5653K bar, whatever the chemistry says. AMS5653K also controls finish condition by product geometry and size, with round bars over 2.75 in (69.8 mm) diameter required to be hot- or cold-finished, solution heat treated, and descaled.

Neither standard specifies the actual solution heat treatment temperature for 316L or the annealing cycle for Ti-6Al-4V. Both leave those parameters to the producer. If a drawing calls out a specific temperature or hold time, that requirement belongs as a separate line in the RFQ, and the way heat treatment fits into machining sequence is covered in heat treatment before or after CNC machining.

Mill length is spec-controlled for AMS5653K bar under clause 5.1: 6 to 20 ft (1.8 to 6.1 m) standard, with no more than 10% of a shipment shorter than 10 ft (3 m). AMS4928X does not fix a mill length. If your part sizes force particular blank lengths, that requirement belongs on the PO. Aerospace supplier quality controls that make these callouts stick are covered in ISO 9001:2026 supplier checks.

4. Medical implant grade: ASTM F136 vs ASTM F138

For permanent load-bearing implants (spinal fixation, hip stems, orthopedic plates), the implant grade titanium specification on the drawing is Ti-6Al-4V ELI per ASTM F136-26. For surgical instruments, short-term fixation devices, and non-load-bearing implants where cost matters more than fatigue life, the medical grade stainless steel specification is 316L per ASTM F138-19. Substituting one for the other on a load-bearing part changes the failure envelope by a wide margin.

ASTM F136-26 2026 revision added cobalt limits to both Tables 1 and 2, updated product form classification, revised the flat tensile specimen out-of-gauge-length break clause, and revised melting requirements. A material certificate issued against F136-13 does not deliver against F136-26, and buyers relying on older test reports need to reverify the cobalt result.

The material identity is Ti-6Al-4V ELI (Extra Low Interstitial), UNS R56401. ELI is not defined in a single sentence in F136-26. It shows through Table 1 interstitial element limits (iron, oxygen, nitrogen, carbon, hydrogen) that are tighter than industrial Ti-6Al-4V under AMS4928X or ASTM B348-25 Grade 5. A supplier delivering “Ti-6Al-4V per B348 Grade 5” does not deliver F136-26 material. UNS R56401 versus UNS R56400 is the numerical shorthand for that distinction.

ASTM F138-19 covers wrought 316L bar and wire for surgical implants, UNS S31673. The clause 3.1.1 maximum cross-sectional area is 103 cm² (16 in²), and fine wire is defined as diameter or thickness under 1.60 mm (0.063 in.). Bar and wire are delivered in one of three conditions (annealed A, cold-worked B, or strain-hardened S) with different mechanical property tables per condition. The Type 316L that appears in ASTM A276-25 (UNS S31603) is not F138 material. Same “316L” name, different acceptance envelope, no automatic substitution.

ISO 5832-1:2024 is the ISO standard for wrought stainless steel used in surgical implants. The standard’s own title uses “wrought stainless steel,” not “316L,” and Note 2 in Clause 1 states the alloy “corresponds to UNS S31673 in ASTM F138 and ASTM F139.” Correspondence is not equivalence. The 2024 revision changed the silicon maximum to 0.75% and added a cobalt limit (Co <0.10%) not present in ISO 5832-1:2016. Clause 4.2 also requires a combined C value ≥ 26 where C = 3.3×%Mo + %Cr, an additional constraint beyond individual element limits.

ISO 5832-3:2021 covers wrought Ti-6Al-4V for surgical implants. Its Table 1 base chemistry (Fe ≤0.3%, O ≤0.2%, C ≤0.08%, N ≤0.05%, H ≤0.015% for bar) is not ELI. Clause 4 Note 2 explicitly states that ELI is a separate condition requiring stricter O and Fe limits. Writing “ISO 5832-3 Ti-6Al-4V” alone does not procure ELI-grade material.

One boundary matters more than any table row. Material specification compliance does not equal finished medical device compliance. ASTM F136-26 covers raw material only. Complete implant qualification also requires biological evaluation per ISO 10993, risk management per ISO 14971, and quality system compliance per ISO 13485. This constraint governs how CNC shops covered under medical device manufacturing can and cannot represent their scope.

5. When 316L is enough vs when Ti-6Al-4V is required

Six axes frame the choice.

Cost. 316L raw bar runs roughly one-quarter to one-sixth the per-kilogram cost of Ti-6Al-4V in the industrial market, based on current commodity pricing. If the application is non-critical and the material spec minimum is met, 316L wins on cost.

Weight. Ti-6Al-4V is roughly 45% lighter per unit volume than 316L. For flight parts, wearable devices, or moving mass in a robotic assembly, that gap can outweigh cost by itself.

Service life under cyclic load. Ti-6Al-4V shows a fatigue endurance ratio around 0.5 for smooth polished bar in air. Annealed 316L runs closer to 0.4. Rotating aerospace components and permanent load-bearing implants favor Ti.

Corrosion environment. Ti-6Al-4V resists chloride pitting in body fluid and marine service. Annealed 316L handles neutral chlorides at ambient, but pitting and crevice attack rise sharply above 60°C in chloride-bearing water. Hot chloride, body fluid, and marine crevice conditions push the selection to Ti.

Service temperature. Annealed 316L retains code-rated strength up to about 425°C (800°F) in ASME pressure service and takes short-term exposure higher. Ti-6Al-4V loses roughly half its room-temperature strength by 315°C (600°F) and is not used above 400°C sustained. Hot-service parts default to 316L or higher-nickel alloys.

Magnetism. Annealed 316L is nominally paramagnetic (permeability under 1.05), but cold work and welding raise magnetic permeability. Ti-6Al-4V stays non-magnetic under all processing. MRI-adjacent devices and magnetic-clean instruments default to Ti.

Neither alloy fits every case. Cobalt chrome (CoCrMo per ASTM F1537) is chosen for articulating implant surfaces such as femoral heads and knee bearing surfaces where wear resistance and biocompatibility drive the selection. Inconel 718 or 625 covers hot service above Ti-6Al-4V’s usable range, at further cost and machining difficulty. Duplex stainless (UNS S31803, “2205”) handles hot chlorides where 316L pits but Ti is overkill. These are alternatives, not defaults; the decision matrix above still frames the primary selection between the two alloys covered here. For structural constraints upstream of this material choice, see DFM design guidelines.

6. CNC machining Ti-6Al-4V vs 316L: cost and lead time

Machinability data comes from published industry references, not from either aerospace or medical spec. The AISI 1212 free-machining benchmark scales as 100%. On that scale, annealed 316L machines at 36 to 45% and annealed Ti-6Al-4V at 22 to 25%. Ti-6Al-4V is roughly half as machinable as 316L, and both trail free-machining carbon steels and aluminum by a wide margin.

Cutting speed reflects that gap. Published carbide-insert cutting speeds run 90 to 120 m/min (300 to 400 sfm) for turning 316L and 40 to 60 m/min (130 to 200 sfm) for turning Ti-6Al-4V, at moderate depth of cut in flood coolant. Tool life for Ti-6Al-4V lands around 30 to 50% of comparable 316L tool life under similar depth-of-cut and coolant conditions. Ti also requires more careful chip evacuation because localized heat concentrates in the tool tip and does not spread into the workpiece.

Surface finish achievable in a finishing pass sits around Ra 0.4 to 0.8 μm for both alloys with a sharp insert and a moderate feed, but Ti-6Al-4V is more sensitive to elastic recovery, which affects final dimension hold. Additional finish improvement to Ra 0.2 μm or better is achievable on either alloy with polishing or lapping.

The composite effect on quotes is direct. For the same drawing on a CNC turn-mill with identical stock removal, Ti-6Al-4V runs two to three times the cycle time of 316L. Combined with the four-to-six-fold material cost gap noted in the opening, a finished Ti-6Al-4V part prices at three to five times the same part in 316L. Understanding how CNC machining tolerances and cost interact with material selection helps buyers size the budget at the RFQ stage, and the CNC machining service page covers the shop scope on both alloys.

7. How to specify Ti-6Al-4V or 316L in your RFQ

A complete material call-out on an aerospace or medical drawing contains six fields: alloy, specification number, revision letter, product form, condition, and any drawing-added constraints (heat treatment temperature, size, mill length, packaging). Missing fields leave interpretation open, and a material certificate cannot resolve ambiguity that the PO never closed.

Aerospace 316L 316L per SAE AMS5653K, solution heat treated, bar, [dia] × [length]

Aerospace Ti-6Al-4V Ti-6Al-4V per SAE AMS4928X, annealed, bar, [dia] × [length]

Medical implant 316L 316L per ASTM F138-19, condition A (annealed), bar, UNS S31673, [dia] × [length]

Medical implant Ti-6Al-4V Ti-6Al-4V ELI per ASTM F136-26, annealed, bar, UNS R56401, [dia] × [length]

Three call-out errors show up on RFQs. Writing “AMS5653” without the revision letter opens the door to older-revision inventory per clause 8.4. A “316L bar” line without the specification number defaults to commercial ASTM A276, which does not carry the aerospace bar-from-plate prohibition or the medical cross-section limit. And “Ti-6Al-4V per AMS 4928” for a medical implant is a category error: AMS 4928 is aerospace and does not enforce the ELI interstitial limits.

Tolerance callouts that pair with these material lines are covered in ISO 2768 Edition 2 for CNC drawings, and drawing conventions for high-precision features are covered in tight tolerance CNC drawings.

Frequently asked questions

What is the difference between ASTM F136 and F138?

F136 covers Ti-6Al-4V ELI (UNS R56401) as wrought bar and forging stock for surgical implants. F138 covers wrought 316L (UNS S31673) as bar and wire for surgical implants. Different alloy families, different UNS numbers, different acceptance envelopes. A device qualified against F136 cannot be built from F138 material.

Can I use commercial 316L per ASTM A276 instead of F138 for a surgical instrument?

Not if the drawing calls out F138. ASTM A276 covers Type 316L bar and shapes for commercial and industrial use (UNS S31603). F138 requires UNS S31673, imposes a maximum bar cross-section of 103 cm² (16 in²), requires intergranular corrosion testing, and controls surface finish condition. A276 material carries none of those constraints.

Does specifying Ti-6Al-4V per AMS 4928 automatically deliver ELI grade material?

No. AMS4928X governs industrial Ti-6Al-4V (UNS R56400) for aerospace. The ELI condition (UNS R56401) sits under ASTM F136-26 or ISO 5832-3 with an added ELI callout. A medical implant drawing needing ELI must read F136-26 or ISO 5832-3 with the ELI grade identified.

Why does aerospace 316L bar cost more than commercial 316L bar of the same size?

The chemistry is close but the acceptance testing, source traceability, and certification burden differ. AMS5653K requires intergranular attack testing per ASTM A262 Practice A or E, prohibits bar cut from plate, controls finish condition by geometry, and requires heat-and-lot certified reports. Those steps add cost the commercial route does not carry.