Why Gr23 Must Be Verified
Gr23 titanium, designated UNS R56401, differs from standard Grade 5 mainly in its lower oxygen and iron content, which gives it the extra fracture toughness required for implantable medical devices. The ELI designation stands for extra low interstitial, referring to oxygen, carbon, nitrogen and hydrogen. Because the price difference is significant, buyers must verify that delivered material is truly Gr23 and not relabeled Grade 5.
Certificate and Marking Review
The first verification step is examining the mill test certificate, which must state the grade as Gr23 or Ti-6Al-4V ELI, the UNS number R56401, the heat number and the certified chemistry. The certificate must show the oxygen content at or below 0.13 percent, the key difference from Grade 5. Physical markings on the material should match the certificate, and any discrepancy is grounds for rejection.
Chemical Analysis
Definitive identification requires chemical analysis of the actual material. The aluminum and vanadium contents confirm that the alloy is Ti-6Al-4V, while the oxygen, iron and other interstitial levels confirm the ELI grade. Oxygen is measured by inert gas fusion analysis, and the result is compared with the 0.13 percent maximum for Gr23. A certified laboratory report is the only fully reliable proof of grade.
Mechanical Property Screening
Gr23 and Grade 5 have similar tensile strength requirements, but the ELI grade shows higher ductility and fracture toughness. Tensile testing that shows elongation at the high end of the Grade 5 range is consistent with Gr23, while low ductility suggests standard Grade 5 or improper processing. Mechanical screening supports the chemical evidence but cannot replace it.
Hardness and Microstructure Checks
Hardness testing and metallographic examination provide additional supporting evidence. Gr23 has an alpha-beta microstructure similar to Grade 5, so microstructure alone cannot separate the grades, but abnormal structures indicate wrong processing. Hardness values near the lower end of the alloy range are consistent with the softer ELI material. These checks help flag suspicious material for full analysis.
Procurement Safeguards
Buyers protect themselves by purchasing only from qualified mills with documented quality systems, requiring certificates from the mill rather than intermediate traders, and performing incoming chemical verification on critical lots. For implant manufacturing, the regulatory framework requires full traceability and certified material. Independent third-party inspection can verify chemistry at the mill before shipment.
Frequently Asked Questions
Q: What is the difference between Gr23 and Grade 5 titanium?
A: Gr23 is the extra low interstitial version of Ti-6Al-4V with maximum 0.13 percent oxygen, giving higher fracture toughness for implant use.
Q: What is the UNS number for Gr23?
A: Gr23 titanium is designated UNS R56401, while standard Grade 5 is UNS R56400.
Q: How is Gr23 identified definitively?
A: Chemical analysis confirming aluminum, vanadium, oxygen and interstitial levels is the definitive identification method.
Q: Why is Gr23 more expensive than Grade 5?
A: The extra low interstitial control requires more careful melting and processing, and the material is certified for medical implant service.
Q: Can Gr23 be identified by hardness alone?
A> A: Hardness screening is only supporting evidence, because chemical analysis is required to confirm the ELI grade.
