Quick Answer
Grade 5 and Grade 23 are both Ti-6Al-4V alloys; the difference is purity, not chemistry. Grade 23 is the “Extra Low Interstitial” (ELI) version of Grade 5, with tighter limits on oxygen (≤0.13% vs. ≤0.20%) and iron (≤0.25% vs. ≤0.40%) . This tighter chemistry gives Grade 23 higher ductility, better fracture toughness, and improved biocompatibility, which is why Grade 23—not Grade 5—is the standard choice for surgical implants . Grade 5 remains the workhorse for aerospace and industrial applications where maximum strength and cost-efficiency matter more than implant-grade purity. The governing standard for Grade 23 in implants is ASTM F136; Grade 5 is typically specified under ASTM B348 .
Key Takeaways
- Grade 23 is a cleaner version of Grade 5. Both contain 6% aluminum and 4% vanadium. The ELI designation limits oxygen to 0.13% max and iron to 0.25% max, compared with 0.20% and 0.40% for Grade 5 .
- Lower interstitials mean better toughness, not higher strength. Grade 23 sacrifices some tensile strength for improved ductility and fracture toughness—properties that matter for implants under cyclic loading .
- ASTM F136 is the implant standard. Grade 23 is specified under ASTM F136 for surgical implants, while Grade 5 is typically covered by ASTM B348 for general industrial use .
- Grade 5 is not “wrong” for medical, but Grade 23 is preferred. Some non-implant medical instruments or equipment may use Grade 5. For implanted devices, Grade 23′s purity profile is the established choice .
- The target URL provided is for Ti-6246 aerospace alloy, not Grade 5 or Grade 23. Buyers seeking implant-grade Ti-6Al-4V ELI should reference the bone screw or spine screw product pages, not the Ti-6246 aerospace page.
The Core Difference: Interstitial Element Limits
What “ELI” Actually Changes
Both grades share the same base chemistry: titanium with 5.5–6.5% aluminum and 3.5–4.5% vanadium. The distinction lies in the interstitial elements—oxygen, nitrogen, carbon, and iron—that occupy the spaces between titanium atoms in the crystal lattice .
| Element | Grade 5 (Ti-6Al-4V) | Grade 23 (Ti-6Al-4V ELI) |
|---|---|---|
| Oxygen (O) | ≤ 0.20% | ≤ 0.13% |
| Iron (Fe) | ≤ 0.40% | ≤ 0.25% |
| Nitrogen (N) | ≤ 0.05% | ≤ 0.03% |
| Carbon (C) | ≤ 0.08% | ≤ 0.08% |
| Hydrogen (H) | ≤ 0.015% | ≤ 0.0125% |
Data sources: Grade 23 limits per ASTM F136 ; Grade 5 limits per ASTM B348 .
Why Oxygen Matters Most
Oxygen is the most influential interstitial element in titanium. Higher oxygen content increases strength but reduces ductility and fracture toughness. The ELI grade’s 0.13% oxygen limit (versus 0.20% for Grade 5) is the primary reason Grade 23 delivers better damage tolerance—a critical property for implants that must withstand years of cyclic loading without cracking .
The Mechanical Property Trade-Off
| Property | Grade 5 (Annealed) | Grade 23 (ELI, Annealed) |
|---|---|---|
| Yield Strength | ~830–880 MPa | ~760–800 MPa |
| Tensile Strength | ~895–950 MPa | ~825–860 MPa |
| Elongation | ~10–14% | ~8–10% |
| Fracture Toughness | Lower | Higher |
Data sources: Grade 5 mechanical properties ; Grade 23 ELI properties .
The numbers reveal the trade-off: Grade 5 is slightly stronger, but Grade 23 is tougher and more ductile. For an implant like a bone screw or hip stem, the ability to deform without fracturing under unexpected loads is more valuable than a marginal increase in yield strength. This is why implant designers specify Grade 23.
Medical Application Standards: Why Grade 23 Is the Implant Grade
ASTM F136 vs. ASTM B348
The standards tell the story of intended use:
- Grade 23: Governed by ASTM F136 (“Standard Specification for Wrought Ti-6Al-4V ELI Alloy for Surgical Implant Applications”) and ISO 5832-3 . The standard title itself specifies surgical implants.
- Grade 5: Typically governed by ASTM B348 (“Standard Specification for Titanium and Titanium Alloy Bars and Billets”), a general industrial specification .
A supplier quoting “ASTM F136″ is explicitly claiming implant-grade material. A supplier quoting “ASTM B348 Grade 5″ is claiming industrial-grade material. These are not interchangeable for implant applications.
Biocompatibility and Clinical Preference
Grade 23′s improved biocompatibility profile is attributed to its lower interstitial content and the resulting cleaner microstructure . While Grade 5 has been used in some medical devices historically, the modern standard for implanted components—particularly load-bearing implants like bone screws, spinal rods, and joint replacements—is Grade 23 ELI.
The target supplier’s bone screw product page references suitability for cortical bone screws, cancellous bone screws, and locking screws—applications where Grade 23 is the appropriate specification.
When Grade 5 Is Appropriate—and When It Is Not
Legitimate Grade 5 Applications
- Aerospace structural components: Where maximum strength-to-weight ratio is critical and interstitial purity is not a clinical concern
- Industrial equipment: Chemical processing, marine hardware, and general engineering where corrosion resistance and strength matter but implant standards do not apply
- Non-implant medical instruments: Surgical tools, instrument trays, and equipment housings that do not contact patient tissue long-term
Where Grade 5 Should Not Be Used
- Implanted devices: Bone screws, spinal fixation, joint components, dental implant bodies—these should specify Grade 23 ELI per ASTM F136
- Long-term tissue contact: Any application where material purity and long-term biocompatibility are regulatory requirements
The distinction is not about quality—Grade 5 is an excellent alloy. It is about fitness for purpose. An aerospace bracket and a spinal screw have different performance requirements, and the standards reflect that difference.
Procurement Verification: What to Check
| Verification Item | Grade 23 (Implant) | Grade 5 (Industrial) |
|---|---|---|
| Standard cited | ASTM F136 or ISO 5832-3 | ASTM B348 or AMS 4911 |
| Oxygen content | ≤ 0.13% | ≤ 0.20% |
| Iron content | ≤ 0.25% | ≤ 0.40% |
| Mill certificate | Must show ELI chemistry | Standard chemistry |
| Melting practice | Typically triple-melted | May be double-melted |
A material certificate that says “Ti-6Al-4V” without specifying ELI or Grade 23 is not sufficient for implant applications. The certificate must explicitly state Grade 23 or Ti-6Al-4V ELI and reference ASTM F136.
FAQ
Is Grade 23 stronger than Grade 5?
No. Grade 5 is slightly stronger in terms of yield and tensile strength. Grade 23′s advantage is toughness and ductility, not strength. The lower oxygen content in Grade 23 reduces strength slightly but improves fracture resistance—a trade-off that favors implant durability .
Can I use Grade 5 titanium for a medical implant?
Regulatory standards and clinical practice generally expect Grade 23 ELI for implanted devices. Grade 5 may be acceptable for non-implant medical instruments or equipment, but for devices that contact tissue long-term, Grade 23′s ASTM F136 compliance is the established requirement. Consult your regulatory pathway and implant design requirements.
What does “ELI” stand for?
Extra Low Interstitial. It indicates tighter limits on oxygen, nitrogen, carbon, and iron compared to standard Grade 5 Ti-6Al-4V .
Is Grade 23 the same as Ti-6Al-4V ELI?
Yes. Grade 23 is the UNS designation (UNS R56401) for Ti-6Al-4V ELI . The terms are used interchangeably in medical and aerospace contexts.
Does the target supplier (Xinnuo) offer Grade 23 for bone screws?
The target URL provided points to Ti-6246 aerospace alloy, not Grade 23. The supplier’s bone screw titanium bar product page describes material for cortical, cancellous, and locking screws, which typically implies Grade 23 ELI. Buyers should request the specific material certificate to confirm ASTM F136 compliance.
Why does Grade 23 have lower strength than Grade 5?
The lower oxygen content in Grade 23 reduces solid-solution strengthening. Oxygen atoms in the titanium lattice impede dislocation movement; fewer oxygen atoms mean less strengthening but greater ductility. This is a deliberate trade-off for implant applications where toughness is prioritized .
How can I verify a supplier is providing genuine Grade 23?
Request: (1) Mill Test Certificate citing ASTM F136 with chemistry showing O ≤0.13% and Fe ≤0.25%; (2) heat number traceability from certificate to bar; (3) confirmation that the supplier’s quality system is certified to ISO 13485 (medical device quality management).
Post time: Nov-10-2026