Titanium Grade 3 (UNS R50550) is a premium Commercially Pure (CP) titanium that bridges the critical engineering gap between highly formable lower grades (Grade 1 and 2) and heavily alloyed, high-strength titanium (Grade 5). This specific grade achieves a significant boost in mechanical strength through a highly controlled, deliberate increase in interstitial Oxygen content, without sacrificing the legendary corrosion resistance inherent to unalloyed titanium.
Weighing nearly half as much as steel, Grade 3 provides a robust strength-to-weight ratio while maintaining absolute immunity to chloride-induced stress corrosion cracking, seawater pitting, and oxidizing acids. Because it balances moderate structural strength with excellent weldability and chemical inertness, UNS R50550 fasteners are heavily specified for aerospace airframe assemblies, pressurized chemical reactors, and heavy-duty marine hardware where Grade 2 simply lacks the necessary tensile yield limits.
| Material Classification | Commercially Pure (CP) Titanium - Moderate Strength |
|---|---|
| UNS Designation | R50550 |
| Microstructure | Single-Phase Alpha Matrix |
| Magnetic State | Completely Non-Magnetic |
| Density | 4.51 g/cm³ (0.163 lb/in³) — Exceptionally Lightweight |
| Size Range | Metric: M3 to M36 | Imperial: #4 to 1-1/2" |
| Primary Attribute | Optimized Balance of Mechanical Strength and Chemical Immunity |
Contains detailed high-pressure vessel clamping thresholds, specific inert-gas shielding parameters for TIG welded assemblies, and anti-galling lubrication matrices for titanium-on-titanium joints.
⬇ DOWNLOAD DATASHEETBecause the structural integrity of Grade 3 relies entirely on precise interstitial gas management, verifying the exact Oxygen content is critical. Ananka ensures that every lot of Grade 3 fasteners is backed by stringent Vacuum Arc Remelting (VAR) certification.
Unlike alloyed titaniums (which use Aluminum or Vanadium), Grade 3 remains Commercially Pure. It achieves its higher strength classification simply by allowing a higher concentration of Oxygen (up to 0.35%) and slightly more Iron compared to Grades 1 and 2, which stiffens the alpha-phase crystal lattice.
| Titanium (Ti) | Oxygen (O) | Iron (Fe) | Carbon (C) | Nitrogen (N) | Hydrogen (H) |
|---|---|---|---|---|---|
| Balance (~99.2) | 0.35 Max | 0.30 Max | 0.08 Max | 0.05 Max | 0.015 Max |
| Mechanical Property | Typical Limits (Annealed Temper) |
|---|---|
| Tensile Strength | 65,000 psi (450 MPa) Minimum |
| Yield Strength (0.2% Offset) | 55,000 - 65,000 psi (380 - 450 MPa) |
| Elongation (in 2 inches) | 18% Minimum |
| Hardness (Brinell) | ~ 200 HB (approx. 93 HRB) |
| Standard / System | Designation |
|---|---|
| ASTM Specifications | ASTM B348 (Rod/Bar), ASTM F467 / F468 (Fasteners) |
| Common Trade Names | CP Titanium Grade 3, Unalloyed Titanium |
| European Equivalent | EN 3.7055 (Ti3) |
| Aerospace Standard | AMS 4921 |
| Mating Bolts/Studs | Internal Threads (Nuts) | Washers / Gaskets |
|---|---|---|
| Grade 3 CP Titanium Hex Bolts | Grade 3 CP Titanium Hex Nuts | Grade 3 Flat Washers / PTFE |
CRITICAL WARNING: Like all titanium alloys, Grade 3 is highly susceptible to severe thread galling (cold-welding) when clamped under tension. If a raw titanium nut is threaded onto a raw titanium bolt without proper lubrication, the friction will cause the threads to seize permanently. Premium dialectric anti-seize pastes or Teflon-based dry films are absolutely mandatory prior to installation.
| Nominal Diameter | Threads Per Inch (UNC) | Max Target Torque (in-lbs) — Lubricated | Max Target Torque (ft-lbs) — Lubricated |
|---|---|---|---|
| 1/4" | 20 | 50 - 60 | ~ 4.5 |
| 5/16" | 18 | 110 - 130 | ~ 10.0 |
| 3/8" | 16 | 190 - 210 | ~ 16.5 |
| 1/2" | 13 | 400 - 450 | ~ 35.5 |
Grade 2 is the most common CP titanium, acting as the "workhorse" of the industry. However, Grade 3 is intentionally specified when an engineering design requires higher tensile strength (approx. 20% stronger than Grade 2) to handle increased pressure or structural loads, but cannot risk using an alloyed titanium like Grade 5, which might be too brittle or chemically reactive in a specific acidic environment.
Yes, Grade 3 has excellent weldability. However, titanium is highly reactive to oxygen and nitrogen at elevated temperatures. Welding must be performed using strictly controlled TIG processes with 100% pure Argon or Helium shielding gas (including a trailing shield and back-purge). If the weld pool is exposed to ambient air, the titanium will absorb oxygen, become severely embrittled, and crack instantly.
No. Grade 3 Titanium is virtually immune to all forms of seawater corrosion, including chloride pitting, crevice corrosion, and microbiologically influenced corrosion (MIC), regardless of the water temperature or velocity. You can leave a Grade 3 titanium fastener submerged in the ocean for a century, and it will remain structurally identical to the day it was installed.
