Grade 5 vs. Grade 23 (ELI): An Insider’s Guide to Choosing Medical Titanium

The Price Difference: Grade 5 vs. Grade 23

Years ago, while sourcing raw material for a new line of orthopedic bone screws, a confusing set of quotes landed on my desk.

On one side was standard Ti-6Al-4V (Grade 5); on the other, Ti-6Al-4V ELI (Grade 23).

Glancing at the chemical specifications, they appeared nearly identical—both roughly 90% Titanium, 6% Aluminum, and 4% Vanadium. Yet, the bottom line told a different story: The Grade 23 (ELI) was about 30% more expensive.

Naturally, skepticism set in. Was this just a ‘medical tax’? It felt like suppliers were simply rebranding the same metal to charge a premium. The temptation to go with the cheaper Grade 5—and impress the boss with the cost savings—was strong.

That would have been a disaster.

Over the years—after dealing with fractured prototypes, angry machinists, and the nightmare of FDA compliance audits—I’ve learned the hard way that the extra cost of ELI isn’t about marketing. It’s about what happens inside the metal structure when it’s inside a human body.

In this guide, I’m going to skip the textbook definitions. Instead, I’ll share the practical lessons we learned on the shop floor. I’ll explain exactly what you are paying for with that 30% premium, why Grade 23 is actually harder to machine (surprise!), and how to decide which grade your project actually needs.

What is “ELI” (Extra Low Interstitials)?

To understand why we pay extra for Grade 23, we have to zoom in—way in.

“ELI” stands for Extra Low Interstitials.

But what are “interstitials”? In the early days, I glossed over this term. I just knew it meant “purity.” But knowing what kind of purity matters. Think of interstitials as tiny “contaminants”—specifically Oxygen, Nitrogen, and Carbon—that get stuck in the empty spaces between the titanium atoms.

Here is the non-textbook way to visualize it:

Imagine the atomic structure of titanium as a perfectly organized military marching band. The soldiers (titanium atoms) are lined up in neat rows.

In Grade 5 (Standard): Imagine someone threw a handful of gravel (Oxygen atoms) into the formation. These rocks get stuck between the soldiers. Now, the formation is very “tight” and rigid. It’s hard to push them out of line because the rocks are blocking them. This makes the metal very strong, but also brittle. If you force it to move, the formation breaks.
In Grade 23 (ELI): We carefully remove most of that gravel. The formation is cleaner. The soldiers can slide past each other smoothly without tripping over rocks. This makes the metal slightly less “hard,” but incredibly “tough.” It can bend and flex under pressure without snapping.

So, the premium you are paying isn’t just for “cleaner” metal. You are paying for the removal of these microscopic “roadblocks.” This leads to the most critical trade-off:

High Oxygen (Grade 5): Higher Strength, Lower Toughness.
Low Oxygen (Grade 23): Lower Strength, Superior Toughness.

Comparison Data: Tensile Strength vs. Fracture Toughness

Here is the trap most new engineers fall into: they look at the datasheet, see that Grade 5 has a higher “Tensile Strength,” and assume it’s the superior material.

I made this mistake early in my career. I chased the highest number on the chart. I was wrong.

Let’s look at the actual numbers side-by-side. These are typical minimum values derived from ASTM F136 (Medical ELI) and ASTM B348 (Industrial Grade 5).

Property	Grade 5 (Standard)	Grade 23 (ELI)	The “Insider” Takeaway
Oxygen (Max)	0.20%	0.13%	Less oxygen = More flexibility.
Iron (Max)	0.40%	0.25%	Less iron = Better corrosion resistance.
Tensile Strength	~895 MPa (Min)	~860 MPa (Min)	Grade 5 is actually stronger (statically).
Fracture Toughness ($K_{IC}$)	~50-60 MPa$\sqrt{m}$	~75-90+ MPa$\sqrt{m}$	Here is the winner. Grade 23 resists cracking much better.

The “Strength Trap”

Standard Grade 5 is technically “stronger.” But in the human body, Tensile Strength is rarely the failure mode.

Think about a hip stem or a bone plate. It doesn’t fail because someone pulled it apart with 1000 MPa of force. It fails because of cyclic loading—walking, chewing, running—millions of times a year.

This is where Fracture Toughness ($K_{IC}$) becomes the only number that matters. It is the material’s ability to stop a microscopic crack from growing into a catastrophic snap. Grade 23 absorbs the energy; Grade 5 snaps.

Machining Reality: Why Grade 23 is Harder to Cut

If you look at the datasheet we just discussed, you might make a logical assumption: “Since Grade 23 (ELI) has less oxygen and is slightly softer than Grade 5, it must be easier to machine, right?”

That was my assumption too. And we paid the price for it.

A few years ago, we switched a dental implant project from Grade 5 to Grade 23 to improve biocompatibility. We expected our tool life to improve.

Within the first hour of the production run, the floor supervisor called me down to the CNC machine. He held up a carbide end mill that looked like it had been dipped in molten wax.

“It’s not cutting,” he told me. “It’s smearing. It’s like trying to machine chewing gum.”

The Hidden Enemy: Galling

This is the dirty secret of ELI titanium. Because Grade 23 is so pure and ductile (thanks to the lack of “roadblock” atoms), it doesn’t chip away cleanly. Instead, it tends to adhere or “weld” itself to the cutting tool. We call this Galling.

To fix this, we couldn’t just “power through.” We had to slow down our cutting speeds significantly to manage the heat.

Why does this matter to you as a buyer? When you see a quote for a Grade 23 part, you aren’t just paying for the premium raw material. You are paying for machine time. A part that takes longer to cut costs more to make.

Application Guide: When to Choose Grade 23 vs. Grade 5

After navigating the microscopic structures and the machining nightmares, you are probably asking: “Okay, but which one do I put on my Purchase Order?”

To keep things simple for my own team, I developed a simple “Traffic Light” rule.

🔴 The Red Zone: MUST USE Grade 23 (ELI)

If your device falls into this category, do not compromise. The risk of fracture is too high.

Permanent Implants: Anything that stays in the body for more than 30 days.
High-Load Applications: Hip stems, knee components, spinal rods.
Small Cross-Sections: Dental implants or tiny bone screws (<3mm).
Why? In these parts, the Fracture Toughness of ELI is your insurance policy against the device snapping inside a patient.

🟢 The Green Zone: SAVE MONEY with Grade 5

If your device falls here, Grade 23 is likely a waste of budget.

Surgical Instruments: Scalpels, retractors, forceps, drill bits.
External Fixators: Those “cages” that hold bones in place but sit outside the skin.
Trials & Sizers: Tools used by doctors to measure the size of an implant during surgery.
Why? Here, you want the higher Hardness of Grade 5 to keep cutting edges sharp. Plus, since they don’t stay in the body, the “biological purity” of ELI is unnecessary.

Compliance Trap: How to Spot Fake Medical Titanium

I cannot stress this enough: Not all “Ti-6Al-4V” is created equal.

A few years ago, we were auditing a new potential supplier. The label on the crate said “Ti-6Al-4V,” and the chemical analysis showed the oxygen levels were low enough to technically pass as ELI. It looked like a bargain.

But something felt off.

I asked them for the full MTR (Material Test Report) and specifically asked to see the “Microstructure Examination” section required by ASTM F136.

The room went quiet.

It turned out they were trying to sell us ASTM B348 (Industrial Grade) titanium. While it chemically matched the medical grade, it had never undergone the rigorous microstructure testing required for implants. It could have had microscopic voids that would cause fatigue failure. We walked away immediately.

My Actionable Advice: When you receive your material certs, look for a specific line item that says “Tested per ASTM F136” or “Microstructure: Acceptable/No Alpha Case.” If that line is missing, do not sign for the shipment.

Cost Breakdown: Raw Material and Machining

Let’s address the elephant in the room: The Budget.

When I present a quote for Grade 23 (ELI) parts, clients often ask, “Can we just switch to Grade 5 to shave 20% off the unit price?”

It’s a fair question. But to answer it, we need to break down exactly where that extra money is going.

The Raw Material Premium (~15-20%): Making ELI titanium isn’t as simple as just “filtering” standard titanium. It requires starting with a higher grade of “titanium sponge” and undergoing additional Vacuum Arc Remelting (VAR) to burn off impurities.
The Hidden “Machining Tax” (~10-15%): Remember the “gummy” machining nightmare? Because we have to run our machines slower to prevent galling, the cycle time increases. In manufacturing, Time = Money.

The Bottom Line: It’s an Insurance Premium

I tell my clients to think of the extra cost not as an expense, but as an insurance premium. The cost of a single FDA recall due to a fractured implant can run into the millions. Compared to that, paying a few extra dollars for the superior toughness of Grade 23 is the cheapest insurance policy you will ever buy.

Final Summary: Making the Right Choice

If there is only one thing you take away from this guide, let it be this distinction:

Grade 5 (Standard) is the “Warrior.” It is rigid, hard, and cost-effective. It holds a sharp edge and fights back against wear. It is the perfect choice for the tools in the surgeon’s hand.
Grade 23 (ELI) is the “Guardian.” It is pure, flexible, and forgiving. It absorbs the shocks of daily life without breaking. It is the only choice for the implant that stays inside the patient’s body.

Navigating the choice between these two materials isn’t just about reading a datasheet; it’s about balancing budget realities with patient safety. Hopefully, this guide saves you from the “gummy” machining surprises and the compliance scares that I faced earlier in my career.

Still Unsure? Let Us Double-Check.

If you are looking at a drawing right now and aren’t 100% sure which grade is specified—or if you have a stack of Material Test Reports (MTRs) that look suspicious—don’t guess.

Contact our engineering team today. We can review your specs and help you source the exact ASTM F136 compliant material your project demands, without the “Trojan Horse” risks.