The Two Most Important Titanium Alloys
Titanium Grade 2 (CP-Ti, UNS R50400) and Grade 5 (Ti-6Al-4V, UNS R56400) represent the two most widely used titanium materials in industry. Grade 2 is the workhorse of commercially pure titanium — chosen for corrosion resistance and formability. Grade 5 is the dominant aerospace alloy — prized for its high strength-to-weight ratio.
Understanding the differences between these two alloys is critical for engineers selecting titanium for chemical processing, aerospace, medical, marine, and energy applications.
Chemical Composition
| Element | Titanium Grade 2 (R50400) | Titanium Grade 5 (R56400) |
|---|---|---|
| Ti | Balance (≥ 99.0%) | Balance |
| Oxygen | ≤ 0.25% | ≤ 0.20% |
| Iron | ≤ 0.30% | ≤ 0.40% |
| Carbon | ≤ 0.08% | ≤ 0.08% |
| Nitrogen | ≤ 0.03% | ≤ 0.05% |
| Hydrogen | ≤ 0.015% | ≤ 0.015% |
| Aluminum | — | 5.5–6.75% |
| Vanadium | — | 3.5–4.5% |
Grade 2 is essentially pure titanium with controlled interstitial elements. Grade 5 adds aluminum (alpha stabilizer) and vanadium (beta stabilizer) to create an alpha-beta alloy with significantly higher strength through heat treatment.
Mechanical Properties Comparison
| Property | Grade 2 (Annealed) | Grade 5 (Annealed) | Grade 5 (Solution Treated & Aged) |
|---|---|---|---|
| Tensile Strength | 345 MPa min | 895 MPa min | 1035 MPa min |
| Yield Strength (0.2% offset) | 275 MPa min | 828 MPa min | 965 MPa min |
| Elongation (% in 50mm) | 20% min | 10% min | 8% min |
| Reduction of Area | 30% min | 25% min | 20% min |
| Hardness (HB) | ~170 | ~334 | ~380 |
| Density | 4.51 g/cm³ | 4.43 g/cm³ | 4.43 g/cm³ |
| Elastic Modulus | 105 GPa | 114 GPa | 114 GPa |
Grade 5 delivers approximately 2.5× the strength of Grade 2 while maintaining similar density — resulting in a dramatically superior strength-to-weight ratio.
Corrosion Resistance
Grade 2: Superior in Most Environments
As commercially pure titanium, Grade 2 offers excellent corrosion resistance in most environments:
- Seawater: Virtually immune to pitting, crevice corrosion, and stress corrosion cracking
- Chloride solutions: Excellent resistance up to high concentrations and temperatures
- Oxidizing acids: Outstanding resistance to nitric acid and chromic acid
- Alkalis: Excellent resistance at all concentrations
- Reducing acids: Good resistance, but may require inhibitors or aeration in dilute HCl and H₂SO₄
Grade 5: Good But Not Equal
Grade 5 has good corrosion resistance in most environments but is not quite as resistant as Grade 2 in certain aggressive conditions:
- Seawater: Good, but susceptible to crevice corrosion at temperatures above 70°C in stagnant conditions
- Crevice corrosion: The alpha-beta structure is slightly more susceptible than alpha structure
- Stress corrosion cracking: Generally resistant, but susceptible in hot concentrated chloride environments
- Galvanic considerations: When coupled with Grade 2 or other CP-titanium, Grade 5 acts as the anode
Key Takeaway
If corrosion resistance is the primary design driver (especially in creviced or stagnant seawater conditions), Grade 2 is the safer choice. For structural applications where corrosion resistance is important but strength is paramount, Grade 5 is acceptable.
Formability and Fabrication
Grade 2 — Excellent Formability
- Can be cold-formed using standard equipment (with consideration for springback)
- Bend radii: 2× thickness (90° bend) for sheet and plate
- Readily machinable with proper techniques (low speed, high feed, copious coolant)
- Weldable by all standard methods — filler metal should match or exceed Grade 2 (ERTi-1 or ERTi-2)
Grade 5 — Limited Formability
- Higher strength means higher forming forces required
- Greater springback than Grade 2 — tooling must account for this
- Bend radii: 4–6× thickness (90° bend) at room temperature
- Hot forming (650–790°C) significantly improves formability
- Machinable but more challenging — galling tendency and work hardening
- Weldable — ERTi-5 filler metal required; post-weld heat treatment recommended
High-Temperature Performance
| Property | Grade 2 | Grade 5 |
|---|---|---|
| Max Continuous Service Temp | 315°C (600°F) | 400°C (750°F) |
| Creep Resistance | Moderate | Good (at elevated temperatures) |
| Oxidation Resistance | Excellent up to 315°C | Excellent up to 400°C |
| Cryogenic Performance | Excellent | Excellent |
Application Comparison
Grade 2 Applications
- Chemical processing: Heat exchangers, reactor vessels, piping in corrosive service
- Desalination: MSF and RO plant tubing, piping, and fittings
- Marine: Condenser tubes, seawater piping, cathodic protection anodes
- Medical: Surgical implants (where biocompatibility is paramount)
- Aerospace: Non-structural components, ductwork, firewalls
- Power generation: Condenser tubing (fossil and nuclear)
Grade 5 Applications
- Aerospace: Airframe structures, jet engine components, landing gear, wing spars
- Medical: Orthopedic implants (hip joints, bone plates), surgical instruments
- Marine: Submarine hull components, propeller shafts, deep-sea equipment
- Sports: Golf club heads, bicycle frames, high-performance fasteners
- Automotive: Racing engine components, valve springs, connecting rods
- Oil & Gas: Downhole tools, risers for high-pressure, high-temperature wells
Cost Comparison
Grade 2 is significantly less expensive than Grade 5:
- Grade 2 sponge price: approximately 30–40% of Grade 5 pricing
- Grade 5 commands a premium due to alloying costs (vanadium is expensive) and more complex processing
- Product forms: Grade 2 is more readily available in all standard forms; Grade 5 lead times may be longer for less common sizes
Decision Matrix
| Design Priority | Choose Grade 2 | Choose Grade 5 |
|---|---|---|
| Maximum corrosion resistance | ✓ | |
| High strength-to-weight ratio | ✓ | |
| Complex cold forming | ✓ | |
| High-temperature strength (200–400°C) | ✓ | |
| Lowest material cost | ✓ | |
| Biocompatibility (implants) | ✓ (bone contact) | ✓ (load-bearing implants) |
| Seawater crevice resistance | ✓ | |
| Fatigue-critical structural parts | ✓ |
Conclusion
Titanium Grade 2 and Grade 5 serve different but complementary roles in engineering design. Grade 2 is the material of choice when corrosion resistance, formability, and cost are the primary concerns. Grade 5 is selected when high strength, fatigue resistance, and elevated-temperature capability are required — even though corrosion resistance and cost are somewhat compromised.
For titanium Grade 2 and Grade 5 in all product forms — sheet, plate, bar, pipe, tube, and fittings — Xi’an Coremetal Steel Co., Ltd. provides certified materials with full traceability and Mill Test Certificates. Contact our team for material selection guidance and quotations.