Titanium Grade 5 vs Grade 2: Alloy Strength vs Pure Simplicity

## What They Are Grade 2 (UNS R50400) is commercially pure (CP) titanium with controlled oxygen content for moderate strength. Grade 5 (UNS R56400), commonly known as Ti-6Al-4V, is the most widely used titanium alloy, accounting for over 50% of all titanium production. | Property | Grade 2 (CP) | Grade 5 (Ti-6Al-4V) | |----------|-------------|---------------------| | Aluminum | None | 6% | | Vanadium | None | 4% | | Oxygen (max) | 0.25% | 0.20% | | Phase | Alpha | Alpha-Beta | | UNS | R50400 | R56400 | ## Mechanical Properties | Property | Grade 2 | Grade 5 (Annealed) | |----------|---------|--------------------| | Tensile Strength | 345 MPa | 930 MPa | | Yield Strength | 275 MPa | 860 MPa | | Elongation | 20% | 14% | | Hardness | 200 HV | 349 HV | | Density | 4.51 g/cm3 | 4.43 g/cm3 | Grade 5 can be further strengthened by solution treating and aging (STA) to reach tensile strengths above 1100 MPa, a capability Grade 2 does not have because CP titanium cannot be precipitation hardened. ## Corrosion Resistance Both grades form a stable, self-healing TiO2 passive film that provides exceptional corrosion resistance. Grade 2 is often preferred for chemical processing because it resists reducing and oxidizing acids, chloride solutions, and wet chlorine gas, and is immune to stress corrosion cracking in most environments. Its lower cost makes it economical for large vessels and heat exchangers. Grade 5 has similar corrosion resistance in most environments but is typically used where strength, not corrosion resistance, is the primary driver. In biomedical applications, the excellent biocompatibility of both grades makes them suitable for implants, with Grade 5 used for load-bearing implants (hip stems, bone plates) and Grade 2 for non-structural applications (dental posts, pacemaker cases). ## Fabrication **Welding**: Grade 2 is readily welded by GTAW (TIG) under argon shielding. The weld retains ductility close to the base metal. Grade 5 is also weldable but requires more stringent gas coverage (trailing shields, backing gas) because the alloying additions make it more sensitive to oxygen and nitrogen contamination. **Forming**: Grade 2 has excellent cold formability, comparable to some austenitic stainless steels. Grade 5 has limited cold formability and is typically hot-formed at 700-950 degrees C. **Machining**: Grade 5 machines better than Grade 2. The higher hardness of Grade 5 produces better chip formation, while Grade 2 tends to gall and smear. Both require sharp tooling, rigid setups, and flood coolant. ## Cost Grade 2 costs approximately 30-50 USD/kg in mill product form. Grade 5 costs 50-100 USD/kg, reflecting the added alloy content and more complex processing. Both are significantly more expensive than stainless steel (3-6 USD/kg for 316L). ## When to Choose Each **Choose Grade 2 when**: Corrosion resistance is the primary requirement, the service stress is moderate, formability and weldability are important, and cost needs to be controlled. Typical applications include chemical processing vessels, heat exchangers, marine hardware, and desalination equipment. **Choose Grade 5 when**: High strength-to-weight ratio is essential, the application is load-bearing, and the budget supports the premium cost. Typical applications include aerospace structural components, turbine blades, medical implants, and high-performance sports equipment.