Why the Choice Matters
Grade 1 and Grade 2 are both commercially pure titanium with the same face-centered-cubic-to-hexagonal crystal structure and the same broad corrosion resistance. They differ in interstitial and impurity limits, which shift the balance between ductility and strength. Choosing the right grade avoids over-specifying expensive purity where strength is needed, and avoids brittle forming or premature corrosion where ductility and low impurity content are essential.
Mechanical Property Requirements
Grade 1 has lower impurity content, especially oxygen at 0.18% maximum and iron at 0.20% maximum, which gives it superior elongation of 24% minimum, higher reduction of area and better toughness; its yield strength is about 170–280 MPa and tensile strength about 240–370 MPa. Grade 2, with oxygen up to 0.25% and iron up to 0.30%, achieves yield strength of about 275–485 MPa and tensile strength of 345–550 MPa, with elongation of 20% minimum. In short, Grade 1 is the formability specialist and Grade 2 the balanced general-purpose grade. For dynamic loads and cryogenic service, Grade 1's lower impurity content reduces embrittlement risk and is preferred for pressure vessels and aerospace components.
Corrosion Environment
In air, fresh water, organic acids and most chemical media, both grades are excellent and the small impurity difference is irrelevant. In chloride-rich media such as seawater and brines, and in crevice-corrosion-prone designs such as heat-exchanger tubes, Grade 1's lower iron, oxygen and carbon content reduces microgalvanic effects and precipitate-induced crevice attack, so it is preferred for long-term immersion service. Grade 2 is acceptable for less severe chloride exposure and coastal structures with regular maintenance, and both grades perform well up to about 400°C; between 400°C and 500°C Grade 2's slightly higher oxygen gives marginally better oxidation resistance, but neither grade is recommended for sustained use above 500°C, where alloyed titanium such as Grade 5 should be considered.
Processing and Fabrication
Grade 1 cold works more easily because of its lower yield strength and higher ductility, which reduces tooling wear and processing cost for deep drawing, rolling, stamping and intricate components. Both grades weld readily by TIG, MIG or plasma methods; Grade 1 produces cleaner welds with lower impurity-induced cracking risk for critical welds such as medical implants and high-pressure systems, while Grade 2's slightly higher iron improves weld-pool fluidity but demands stricter parameter control. For machining, neither grade is easy because titanium's low thermal conductivity drives tool wear, but Grade 1's lower hardness (about HB 110 or less) makes it marginally easier to machine than Grade 2 (about HB 135 or less).
Temperature, Cost and Standards
For cryogenic to ambient service down to -253°C, Grade 1 is the optimal choice because its low impurity content prevents brittle behavior and preserves ductility. For service from 200°C to 400°C, Grade 2 is preferred for its better strength retention and creep resistance. On cost, Grade 2 is the most widely produced CP grade and is typically more economical, while Grade 1 is usually about 10–20% more expensive because of tighter impurity control; specify Grade 1 only when its ductility, toughness or corrosion performance is decisive. Both grades are covered by ASTM B265 (sheet, strip and plate), ASTM B348 (bar), ASTM B338 (seamless tube) and AMS 4900/4901, with Grade 1 commonly required for medical devices under ISO 5832-2 and cryogenic equipment under ASME Section VIII.
FAQ
Which grade is easier to form, Grade 1 or Grade 2?
Grade 1. Its lower yield strength and higher elongation (24% minimum) make deep drawing, bending and severe cold forming easier and less prone to cracking.
Which grade is stronger, Grade 1 or Grade 2?
Grade 2. Its higher oxygen and iron limits raise yield strength to 275 MPa minimum and tensile strength to 345 MPa minimum, versus about 170 MPa and 240 MPa minimum for Grade 1.
Which grade should I choose for seawater service?
For long-term immersion and crevice-prone designs, Grade 1's lower impurity content gives the best resistance; for less severe exposure, Grade 2 is acceptable and more economical.
Why is Grade 1 preferred for cryogenic service?
Its low interstitial content preserves ductility and toughness at temperatures down to -253°C, avoiding the embrittlement that higher-impurity material can show.
Is Grade 1 or Grade 2 more expensive?
Grade 1 is typically 10–20% more expensive because tighter impurity control raises refining and processing cost; use it only when its properties are required.
What are the UNS numbers for Grades 1 and 2?
Grade 1 is UNS R50250 and Grade 2 is UNS R50400, both under ASTM B265 and related product specifications.
