Commercially Pure Grade 1 and Grade 2 Titanium vs Grade 5 Ti-6Al-4V: Key Differences
Nov 24, 2025
Titanium is supplied in a broad family of grades, and the difference between them decides how a finished component behaves once it is in service. The three grades most often compared during specification reviews are Grade 1 and Grade 2 commercially pure (CP) titanium and Grade 5, the Ti-6Al-4V alloy. All three resist chloride-bearing water and oxidising media far better than carbon steel or stainless steel, yet they differ in purity, alloy content, strength, formability and cost. Matching the grade to the duty, instead of defaulting to the strongest option, is what keeps pressure equipment, heat exchangers and structural parts safe and economical at the same time.
Chemical Composition at a Glance
Commercially pure grades are unalloyed titanium held within tight limits on interstitial elements, while Grade 5 adds aluminium and vanadium as deliberate alloying additions. The table below summarises the limits that separate the three grades.
| Element | Grade 1 (UNS R50250) | Grade 2 (UNS R50400) | Grade 5 (UNS R56400) |
|---|---|---|---|
| Oxygen, max % | 0.18 | 0.25 | 0.20 |
| Iron, max % | 0.20 | 0.30 | 0.30 |
| Nitrogen, max % | 0.03 | 0.03 | 0.05 |
| Carbon, max % | 0.08 | 0.08 | 0.08 |
| Hydrogen, max % | 0.015 | 0.015 | 0.015 |
| Aluminium % | none | none | 5.50 to 6.75 |
| Vanadium % | none | none | 3.50 to 4.50 |
| Titanium | Balance | Balance | Balance |
Oxygen is the single most influential interstitial element in the commercially pure grades: it raises strength while reducing ductility. That is why Grade 1 and Grade 2 differ mainly in oxygen content rather than in alloy additions.
Mechanical Properties Compared
| Property | Grade 1 | Grade 2 | Grade 5 |
|---|---|---|---|
| Tensile strength, min | 240 MPa | 345 MPa | 895 MPa |
| Yield strength (0.2 % offset), min | 138 MPa | 275 MPa | 828 MPa |
| Elongation, min | 24 % | 20 % | 10 % |
| Reduction of area, min | 30 % | 30 % | 25 % |
| Density | 4.51 g/cm3 | 4.51 g/cm3 | 4.43 g/cm3 |
| Elastic modulus, typical | about 103 GPa | about 103 GPa | about 114 GPa |
| Practical service temperature | up to about 300 C | up to about 300 C | up to about 400 C |
Grade 5 delivers roughly three times the yield strength of Grade 2 while remaining about 40 % lighter than an equivalent steel section, which is why it dominates aerospace and high-performance engineering. Grade 1 and Grade 2 are chosen instead where the part must be formed, bent, expanded or welded extensively and where the mechanical duty is moderate.
Corrosion Resistance, Formability and Weldability
Oxidising and neutral chloride media: Grade 1 and Grade 2 form a stable passive oxide film and are the preferred choice in seawater, brine, hypochlorite and wet chlorine service.
Grade 5 in corrosive duty: performance is close to the commercially pure grades in most environments, but the alloying additions reduce ductility and slightly reduce resistance in some aggressive reducing media.
Hot reducing acids: where CP titanium is attacked, the molybdenum-bearing Grade 12 or palladium-stabilised grades are specified instead of Grade 5.
Formability: Grade 1 is the most formable and weldable, followed by Grade 2. Grade 5 requires higher forming forces, tighter control of springback and stress relief after welding.
Fabrication behaviour: all three grades conduct heat poorly, so low cutting speeds, generous coolant flow and sharp tooling are needed to avoid work hardening and galling.
Typical Industrial Applications
Grade 1: chemical process vessels, heat exchanger tube, seawater piping, desalination plant, electroplating racks and anodes.
Grade 2: the general-purpose CP grade for pressure vessels, storage tanks, tube and pipe, flanges, fittings and condenser tubing. It is the most widely stocked titanium grade in industry.
Grade 5: aerospace structural parts, landing gear components, engine hardware, surgical implants, high-pressure hydraulic fittings, subsea equipment and high-load fasteners.
Grade 5 ELI (ASTM F136): the extra-low-interstitial variant, used where fracture toughness and fatigue life matter, such as implants and critical forgings.
Selection Guidance for Project Engineers
Begin with the environment rather than the strength figure. If the medium is seawater, brine, hypochlorite or wet chlorine and the component is formed or welded, Grade 2 usually satisfies the duty at the lowest cost, with Grade 1 reserved for severe forming such as deep-drawn or expanded tube. If the component carries high mechanical load, sees elevated temperature or must save weight, Grade 5 is the appropriate selection and fabrication must be planned around its lower ductility, including full argon shielding, qualified welding procedures and post-weld stress relief. Where the medium is a hot reducing acid, neither Grade 2 nor Grade 5 is adequate and a molybdenum-bearing grade should be evaluated. Document the grade, the governing standard and the delivery condition on the purchase specification, because properties such as minimum yield strength are guaranteed by the material standard rather than by the mill certificate alone.
Frequently Asked Questions
Q: What is the main difference between Grade 1 and Grade 2 titanium?
Both are unalloyed commercially pure titanium. Grade 1 is limited to 0.18 % oxygen and Grade 2 to 0.25 % oxygen, so Grade 1 is softer, more ductile and easier to form, while Grade 2 offers higher strength with slightly lower elongation. Grade 2 is the more common industrial choice.
Q: Is Grade 5 titanium as corrosion resistant as Grade 2?
In seawater, brine and most oxidising media the two behave similarly, and the passive film protects Grade 5 just as effectively. In hot reducing acids the commercially pure grades are already unsuitable, and a molybdenum-bearing grade such as Grade 12 should be used for either application.
Q: Can the three grades be welded to each other?
Yes. Grade 1, Grade 2 and Grade 5 are all alpha or alpha-beta titanium alloys and can be joined with matching filler metals such as ERTi-1, ERTi-2 and ERTi-5, provided the joint is protected by argon on both faces and the procedure is qualified. Dissimilar joints should be qualified separately because the weld pool chemistry differs from both parent metals.
Q: Which grade should be used for seawater piping?
Grade 2 is the standard selection for seawater pipe, fittings and condenser tube. Grade 1 is used where the tube is expanded or bent severely, and Grade 5 only where high mechanical loads or high pressure rule out the commercially pure grades.
Q: How hot can each grade be used?
Commercially pure grades are normally limited to about 300 C in continuous service because strength falls and oxidation accelerates above that level. Grade 5 retains useful strength to about 400 C, and the extra-low-interstitial variant trades a small amount of strength for improved toughness.
Q: Which standards cover these grades?
ASTM B265 covers plate, sheet and strip, ASTM B338 covers seamless and welded tube, ASTM B348 covers bar and billet, ASTM B381 covers forgings, and ASTM F136 covers the extra-low-interstitial Grade 5 medical grade. Equivalent ASME SB numbers apply for pressure equipment.
