Commercially Pure Titanium Grades Explained, With Grade 1 in Focus
Nov 26, 2025
Commercially pure titanium is not one material. Four unalloyed grades are defined by the same specifications, and the difference between them is almost entirely a matter of how much oxygen the metal is allowed to contain. Understanding that single variable is enough to select between them correctly.
Why Oxygen Is the Real Alloying Element
Oxygen dissolves in the titanium lattice as an interstitial element and strengthens it substantially, at the cost of ductility. Raising the oxygen limit from 0.18 % to 0.40 % roughly doubles the tensile strength of the grade, which is why the four unalloyed grades form a ladder of strength running from the softest and most formable to the strongest and least formable. Iron and nitrogen act in a similar direction, and all three are capped individually in the specification, but oxygen is the element that changes by the largest amount across the grade ladder and the one most often used to describe the grades.
The Four Unalloyed Grades Compared
| Grade | Oxygen, max | Iron, max | Tensile, min | Yield, min | Elongation, min |
|---|---|---|---|---|---|
| Grade 1 | 0.18 % | 0.20 % | 240 MPa | 138 MPa | 24 % |
| Grade 2 | 0.25 % | 0.30 % | 345 MPa | 275 MPa | 20 % |
| Grade 3 | 0.35 % | 0.30 % | 450 MPa | 380 MPa | 18 % |
| Grade 4 | 0.40 % | 0.50 % | 550 MPa | 483 MPa | 15 % |
Carbon is limited to 0.08 % and hydrogen to 0.015 % in all four grades under ASTM B265, the specification for titanium strip, sheet and plate, with parallel requirements in ASTM B338 for tube and ASTM B348 for bar. Corrosion resistance is essentially the same for all four in most environments, so the choice of grade is normally made on strength and formability rather than on corrosion performance.
Grade 1 in Detail
Grade 1 is the softest and most ductile of the group. The specification fixes a minimum tensile strength of 240 MPa and a minimum yield strength of 138 MPa with 24 % minimum elongation, and because the oxygen is held to 0.18 % maximum the metal bends, deep draws, spins and expands into a tubesheet with less risk of cracking than any other grade. When a component needs a tight bend radius, a deep formed shape, or a rolled tube joint that has to seal, Grade 1 gives the fabricator the most working room.
The limitations are equally clear. It has the lowest strength of the four, so it is the wrong choice for a loaded structural member where Grade 2 or Grade 4 would allow a thinner section. It is also the grade whose strength varies most with a small change in oxygen, so ordering to the low end of the oxygen range is a deliberate specification decision rather than a default.
Where Grade 1 Wins
Grade 1 is selected for chemical processing equipment handling chlorides and oxidising acids, desalination and seawater systems, plate and frame exchanger plates, anodes and cathodes in electrochemical plant, food and pharmaceutical contact surfaces where a non-toxic and readily cleaned surface is required, and medical implants and instruments where biocompatibility and formability both matter. Its resistance to seawater, chlorides and a wide range of chemicals is the reason it appears in marine and desalination components, and its lack of magnetic response is useful in instruments and in equipment where magnetic interference would be a problem.
When to Move Up the Ladder
Moving from Grade 1 to Grade 2 is the normal step when a modest strength increase is needed without giving up much formability, and Grade 2 is the general purpose workhorse of the unalloyed family. Grade 3 is used where the strength of Grade 2 is not sufficient at the permitted section. Grade 4, with oxygen up to 0.40 %, offers the highest strength of the unalloyed grades and is used for fasteners, valve parts and moderate duty structural components, at the cost of reduced ductility and more difficulty in forming. Where higher strength is needed at a lower weight, the alloyed Grade 5 takes over, and where crevice corrosion in hot chlorides is the constraint, the palladium stabilised grades are the answer.
Fabrication Notes
Titanium work hardens rather than thinning locally, so forming operations benefit from generous bend radii and from planning the number of forming steps rather than relying on one large deformation. All welding and thermal cutting must be shielded with inert gas until the metal cools below roughly 400 °C, since titanium absorbs oxygen and nitrogen readily when hot. Machining needs sharp tooling, low cutting speed and effective coolant, because titanium conducts heat poorly and the cutting edge absorbs the heat instead of the chip. Pickling after forming or welding removes surface oxide and any iron contamination, and it must be followed by thorough rinsing to avoid leaving residue that could later promote hydrogen uptake.
Frequently Asked Questions
Q: What is the difference between Grade 1 and Grade 2 titanium?
A: Oxygen content. Grade 1 allows 0.18 % maximum against 0.25 % for Grade 2, which makes Grade 1 more ductile and formable and Grade 2 stronger, with minimum tensile strengths of 240 MPa and 345 MPa respectively.
Q: Why is Grade 1 described as commercially pure if it contains oxygen?
A: It contains no deliberate alloying addition. Oxygen is an interstitial impurity that is controlled to a specification limit, and it is that limit which sets the strength of each unalloyed grade.
Q: Does Grade 1 have better corrosion resistance than Grade 2?
A: They are effectively equivalent in most environments because both rely on the same passive oxide film. The choice between them is normally driven by formability and strength rather than corrosion performance.
Q: What are the typical uses of Grade 1 titanium?
A: Chemical processing equipment, desalination and seawater systems, electrochemical anodes and cathodes, food and pharmaceutical contact equipment, and medical implants and instruments where formability and biocompatibility matter.
Q: How does Grade 4 differ from the lower grades?
A: Grade 4 permits up to 0.40 % oxygen and 0.50 % iron, giving a minimum tensile strength of 550 MPa and yield strength of 483 MPa, which is the highest of the unalloyed grades but comes with 15 % minimum elongation and reduced formability.
