Guides / Grades

Grade 23 ELI Titanium and the Paperwork That Comes With It

Grade 23 is Grade 5 with the interstitial elements held down. Same nominal 6 percent aluminium and 4 percent vanadium, tighter ceilings on oxygen, nitrogen, carbon, hydrogen and iron. ELI stands for extra low interstitial.

That is a small change in chemistry and a large change in what the material is for, and in what it costs to buy a part in it.

What extra low interstitial actually changes

Interstitial elements sit in the gaps in the crystal lattice. They pin dislocations, which raises strength and lowers toughness. Capping them trades one for the other.

Property	Grade 5	Grade 23 (ELI)
Max oxygen	around 0.20 percent	around 0.13 percent
Max iron	around 0.40 percent	around 0.25 percent
Minimum tensile strength	around 895 MPa	around 860 MPa
Fracture toughness	Good	Better
Ductility	Good	Better
Cryogenic behaviour	Acceptable	Preferred

So Grade 23 is marginally weaker and meaningfully tougher. A crack that would propagate in Grade 5 has a harder time in Grade 23. For a load bearing part inside a human body, or a part at liquid helium temperature, that is the property that matters.

Where Grade 23 is specified

Medical implants. This is the big one. ASTM F136 covers Ti-6Al-4V ELI bar and wire for surgical implants, and ISO 5832-3 is the matching international standard. Hip and knee components, spinal cages and screws, trauma plates, dental abutments.

Cryogenic service. Grade 23 keeps its toughness where standard Grade 5 turns brittle, so it appears in cryogenic vessels and fittings.

Offshore and subsea. Where a fracture mechanics case has to be made for the part rather than a simple yield check.

Outside those three, Grade 23 is usually the wrong call. You are paying for toughness you do not need, from a smaller pool of stock.

Why the price gap is not about machining

Buyers sometimes assume Grade 23 costs more because it is harder to cut. It is not. Cutting data, insert grades, coolant pressure and fixturing are the same as Grade 5. A programmer would not change the toolpath.

The cost sits in three other places.

Stock. Fewer mills make it, fewer distributors hold it, fewer sizes are on the shelf. A diameter that is a phone call away in Grade 5 can be a six week wait in Grade 23.

Certification. An F136 heat is tested more thoroughly than a B348 heat. That cost is in the bar before your shop touches it.

Traceability inside the shop. This is the part buyers underestimate. When a bar is cut into blanks, the heat number has to follow every blank. That means transfer marking before the original marking is machined away, segregated storage, controlled paperwork and a QC signature. It is a process, not a photocopy, and a shop that does it properly charges for it.

What a compliant traceability chain looks like

1. The mill issues a certificate for the heat, tested to F136, with the heat number on the bar.
2. The shop receives it, records the heat number against the purchase order and segregates it from other grades.
3. Before any cut removes the marking, the heat number is transferred to each blank and witnessed.
4. Work in progress stays identified through every operation and every outside process.
5. The finished parts ship with a certificate of conformity that names the heat number and the original mill certificate.

If any link breaks, the parts are no longer traceable and, for an implant, no longer usable. This is why a shop that has never done it should not learn on your order.

ISO 13485 and what it does and does not mean

ISO 13485 is the quality management standard for medical device manufacture. A shop holding it has documented processes for traceability, change control, validation and complaint handling.

It is not a titanium capability and it is not a guarantee of machining skill. Plenty of ISO 13485 shops are better at paperwork than at cutting Ti-6Al-4V. Ask about both separately.

Ask for ISO 13485 when your device file requires it, which usually means the part is a finished device or a component you will not further process under your own system. Otherwise ISO 9001 plus a demonstrated traceability process may be enough, and it widens your supplier pool considerably.

What to put on the RFQ

• The grade: Grade 23, Ti-6Al-4V ELI.
• The standard: ASTM F136 or ISO 5832-3, whichever your device file names.
• Whether you need an ISO 13485 shop, honestly assessed.
• Whether you need a certificate of conformity naming the heat number, which you almost certainly do.
• Any cleanliness or passivation requirement, and the specification it is called to.
• Surface finish, because implant surfaces are often specified in Ra and sometimes in more than that.

Say all of it up front. A Grade 23 quote built on the assumption of Grade 5 paperwork is not a quote you can use.

Frequently asked questions

Keep reading

• Grade 2 vs Grade 5 Titanium: Picking the Right Grade for a Machined Part
• A Titanium Grades Chart for People Who Have to Buy Machined Parts