Ti Gr 9 (3.7194 / UNS R56320) Seamless Tubing for Bicycle Frames and Aircraft Lines
Oct 20, 2025
What Grade 9 Is and Where It Fits
Ti-3Al-2.5V, designated Grade 9 in the ASTM system and 3.7194 in the European material numbering system, with UNS number R56320, is an alpha-beta alloy that is sometimes described as half of Ti-6Al-4V. It offers higher strength than the commercially pure grades, and it is significantly easier to form and bend than the Ti-6Al-4V workhorse alloy. Its main product form is seamless tubing, used in the aircraft and leisure industries for bicycle frames, wheelchair frames and golf club shafts.
Two delivery conditions dominate the market. Annealed material is the ductile, general-purpose condition. Cold worked and stress relieved material, usually abbreviated CWSR, is drawn to the final size without a full anneal and carries about 40 % higher strength as a result.
Material Data
| Item | Value |
|---|---|
| Alloy | Titanium 3Al-2.5V |
| Material number | 3.7194 |
| UNS | R56320 |
| Density | 4.48 g/cm³ |
| Elastic modulus | 100 GPa |
| Shear modulus | 44 GPa |
| Melting range | Below 1,700 °C |
Chemistry
| Element | Range or maximum | Role |
|---|---|---|
| Al | 2.5–3.5 % | Alpha stabiliser, strength |
| V | 2.0–3.0 % | Beta stabiliser, formability |
| O | 0.15 % max | Strength and transus control |
| Fe | 0.25 % max | Beta stabiliser, impurity control |
| H | 0.015 % max | Hydride embrittlement |
| Ti | Balance | Matrix |
Oxygen in particular is worth watching. At 0.15 % maximum the grade is more tolerant than an implant-grade ELI material but tight enough that the strength difference between a low-oxygen and a high-oxygen heat is visible in the tensile result, which is why tube mills qualify each heat rather than certifying to the grade average.
Mechanical Properties by Condition
| Condition | Tensile strength | 0.2 % yield strength | Elongation, 2 in |
|---|---|---|---|
| Annealed | 620 MPa | 485 MPa | Reported per specification |
| Cold worked and stress relieved | 861 MPa | 724 MPa | Lower than annealed |
That strength range is what makes the grade useful. A bicycle frame built from CWSR tubing can be laid out with thinner walls than an annealed equivalent, which saves weight without losing the stiffness that governs ride quality, because the elastic modulus of 100 GPa does not change with the delivery condition.
Tube Specifications and Supply Range
ASTM B338 covers seamless and welded titanium and titanium alloy tube for condenser and heat exchanger service and is the specification most frequently quoted for Grade 9 tube. ASTM B861 covers seamless titanium tube for general service and ASTM B337 covers welded tube, both of which include the grade in their scope. For aircraft hydraulic and pneumatic lines the governing requirement is AMS 4943, which sets the annealed and CWSR mechanical values quoted above and adds the cleanliness, dimensional and examination requirements that an aerospace tube system demands.
| Parameter | Typical range |
|---|---|
| Outside diameter, general seamless tube | 3–114 mm |
| Outside diameter, frame and aircraft tube | 4–60 mm |
| Wall thickness | 0.5–10 mm |
| Wall thickness, bicycle frame sets | 0.8–1.2 mm |
| Length | Up to 6 m, or cut to length |
| End finish | Plain, bevelled, threaded |
| Documentation | EN 10204 type 3.1, radiography on request, third party inspection |
Forming, Welding and Bicycle Frame Practice
Grade 9 tubing bends and swages more readily than Ti-6Al-4V, which is why it has been the default material for titanium bicycle frames. Frame builders normally work with butted tube sets, where the wall is thicker at the ends than in the middle, so that the heat-affected zone from welding has material to work with and the middle section stays light. Tube ends are mitred to fit and then welded, most often by TIG in an argon-purged enclosure, because the arc and the hot metal must be shielded from air until the temperature drops below roughly 400 °C.
Cold working changes the rules after welding. A CWSR tube that is bent cold will retain a residual stress pattern that adds to the welding stress, and a stress relief treatment after forming is normal practice on any tube that has been bent beyond a modest radius. Mandrel bending with internal support is used to avoid ovality and wall thinning on the outside of the bend.
In aircraft service, the same tube carries hydraulic fluid at pressure, so the acceptance route is stricter: dimensional tolerance on outside diameter and wall, hydrostatic proof testing when the purchase order calls for it, eddy current or ultrasonic examination, and full traceability from tube to heat number. Because the walls are thin, a scratch or a handling dent is a genuine defect rather than a cosmetic one.
Frequently Asked Questions
Q: Why is Grade 9 used for bicycle frames instead of Ti-6Al-4V?
A: Because it forms and bends much more easily while still being considerably stronger than commercially pure titanium, and its lower modulus gives the compliant ride that frame designers want.
Q: What is the difference between annealed and CWSR tubing?
A: Annealed tube has been recrystallised and is ductile with a 620 MPa tensile floor. CWSR tube is cold drawn and stress relieved, giving 861 MPa tensile and 724 MPa yield with reduced elongation.
Q: Which specification should a bicycle frame tube order cite?
A: ASTM B338 for seamless tube, with the chemistry and mechanical values of Grade 9. Aerospace line tubing goes to AMS 4943, which adds cleanliness and examination requirements.
Q: Can Grade 9 tube be welded to other titanium grades?
A: Yes. Matching filler is usual, and the joint quality depends on gas shielding rather than on the grade combination. Weld colour is the quickest field indicator of shielding quality.
Q: Why is a stress relief needed after bending?
A: Cold bending leaves residual stress that adds to service and welding stress. A stress relief returns the tube closer to the delivered condition and reduces the risk of stress corrosion and dimensional movement in service.
Q: How does Grade 9 perform in seawater and hydraulic fluid?
A: It resists pitting, crevice and erosion corrosion well, so it is used for seawater and hydraulic service on aircraft and marine equipment, where its thin walls also reduce system weight.
