Guides / Grades

Grade 2 vs Grade 5 Titanium: Picking the Right Grade for a Machined Part

Almost every titanium RFQ lands on one of two grades. Grade 2, commercially pure titanium, or Grade 5, the Ti-6Al-4V alloy. The choice moves the price more than most geometry decisions do, so it is worth settling before you send the drawing rather than after the quote comes back.

What the two grades actually are

Grade 2 is commercially pure titanium. It is not chemically pure, it carries small amounts of oxygen, iron, carbon and nitrogen, and the oxygen content is what separates Grade 1, 2, 3 and 4 from each other. More oxygen means more strength and less ductility.

Grade 5 is an alpha beta alloy, nominally 6 percent aluminium and 4 percent vanadium, which is where Ti-6Al-4V gets its name. Those two additions change the crystal structure and roughly triple the strength. They also make it harder to cut, harder to weld and more expensive as stock.

Property	Grade 2 (CP)	Grade 5 (Ti-6Al-4V)
Minimum tensile strength	around 345 MPa	around 895 MPa
Minimum yield strength	around 275 MPa	around 828 MPa
Elongation	around 20 percent	around 10 percent
Density	4.51 g/cm3	4.43 g/cm3
Useful temperature	to roughly 300 C	to roughly 400 C
Heat treatable	No	Yes
Relative bar price	Lower	Higher

Figures are typical specification minimums from the common ASTM bar standards. A mill certificate for your actual heat will read higher than the minimum, often noticeably higher.

Where Grade 2 is the right answer

Grade 2 exists because titanium’s headline property is not strength, it is corrosion resistance. Grade 2 has the same oxide layer as Grade 5 and behaves the same way in sea water, wet chlorine and oxidising acids, but it costs less and machines faster.

Pick Grade 2 when:

• The part lives in sea water, brine or bleach and stainless would pit or crevice corrode.
• The part is a heat exchanger plate, a pipe fitting, a valve internal or a tank component.
• The assembly is welded rather than bolted.
• The part needs to be formed or bent after machining.
• The load case is mild and you were only reaching for Grade 5 out of habit.

That last one is worth repeating. A meaningful share of drawings that call Grade 5 would do the same job in Grade 2, and nobody checked.

Where Grade 5 is the right answer

Grade 5 is about 50 percent of all titanium used worldwide, and for machined parts the share is higher still. It is the grade you reach for when the part carries load.

Pick Grade 5 when:

• The part is structural: a bracket, a fitting, a lug, an upright, a hub.
• You are replacing steel and the whole point is the weight saving.
• The part is an implant or an instrument and the specification calls Ti-6Al-4V or its ELI version.
• Service temperature runs above what aluminium tolerates.
• Fatigue life matters and the section is thin.

What each grade does to the quote

This is the part buyers feel. Grade 5 costs more twice over, once in the stock and again on the machine.

Line in the quote	Grade 2	Grade 5
Bar and plate cost	Lower per kilo	Higher per kilo
Typical carbide surface speed	around 80 m/min	around 50 m/min
Tool wear	Moderate	High, inserts change more often
Chip behaviour	Gummy, wants sharp tools and a steady feed	Stringy and hot, wants high pressure coolant
Deburring	More burr, softer material	Less burr, harder edges
Typical tolerance held	±0.05 mm general	±0.05 mm general, ±0.01 mm on called features

Both grades want the same three things from the shop: a rigid setup, a sharp tool and coolant that reaches the cutting edge. Grade 5 simply punishes the absence of any of them harder.

One habit that surprises buyers: Grade 2 is not automatically the easier material on the shop floor. It is softer and gummier, so it smears and builds up on the edge if the feed drops. Shops that cut a lot of Grade 5 sometimes quote Grade 2 slowly because they treat it like Grade 5. Ask.

Grade 23 ELI, and the other grades worth knowing

Grade 23 is Grade 5 with tighter limits on interstitial elements, mainly oxygen and iron. ELI stands for extra low interstitial. Mechanically it is slightly weaker and considerably tougher, which is why it is the implant grade. On the machine it behaves like Grade 5. The difference a shop feels is paperwork, not cutting data.

A few others come up:

• Grade 9, Ti-3Al-2.5V. Between the two on strength, common as tube, popular in bicycle frames and hydraulic lines.
• Grade 7 and Grade 11. Grade 2 and Grade 1 with a small palladium addition, for crevice corrosion in hot chloride.
• Grade 12. Nickel and molybdenum added for the same reason, cheaper than Grade 7.
• Grade 1, 3 and 4. The rest of the commercially pure family, separated by oxygen content. Grade 1 is the softest and most formable.

A decision table you can use on the drawing

The part	Grade to quote	Why
Sea water pump housing	Grade 2	Corrosion, not load
Aerospace bracket	Grade 5	Load, weight, specification
Heat exchanger plate	Grade 2	Formed and welded
Surgical instrument	Grade 5	Strength and stiffness
Implant component	Grade 23 ELI	Toughness and traceability
Bicycle or motorcycle frame tube	Grade 9	Supplied as tube
Hot chloride valve internal	Grade 7 or Grade 12	Crevice corrosion
Watch case or knife scale	Grade 5	Hardness, finish, anodizing

What to write on your RFQ

If the grade is fixed by a specification, name it and say it is fixed. If you picked it yourself, say so, and add one line about the service conditions: what the part touches, what temperature it sees and what load it carries.

A shop that cuts titanium every week will tell you when a cheaper grade would do the same job. That single line on the RFQ is often worth more than any negotiation on the hourly rate.

Frequently asked questions

Keep reading

• A Titanium Grades Chart for People Who Have to Buy Machined Parts
• Grade 23 ELI Titanium and the Paperwork That Comes With It