Commercially Pure Titanium

Classification & Characteristics

Commercially pure titanium is unalloyed titanium with small traces of impurities such as carbon, hydrogen, iron, nitrogen, and oxygen. It is classified into four ASTM grades: Grade 1, Grade 2, Grade 3 and Grade 4, which have varying amounts of impurities. The CP titanium generally has more than 1000 ppm oxygen and iron, nitrogen, carbon, and silicon as principal impurities. Because small amounts of interstitial impurities greatly affect the mechanical properties of pure titanium, it is not convenient to distinguish the various grades of unalloyed titanium on the basis of chemical analysis. Titanium mill products are more readily distinguished by mechanical properties.

For ASTM Grade 1, 2, 3, 4 in sequence, as the impurity content goes up, the corrosion resistance, room-temperature ductility and formability are reduced but the strength goes higher. In general, commercially pure (CP) titanium is useful in applications requiring high ductility for fabrication as well as high corrosion resistance and good weldability but relatively low strength in service.

Crystal Structure & Transus Temperatures

Commercially pure titanium has several crystal structures, each of which is only stable within particular temperature ranges. The complete transformation from one into another crystal structure is called allotropic transformation; the respective transformation temperature is called the transus temperature. Pure titanium crystallizes at low temperatures in a modified ideally hexagonal close-packed (hcp) structure, called α titanium. At high temperatures, however, the body-centered cubic (bcc) structure is stable and is referred to as β titanium. The atomic unit cells of the hexagonal close packed (hcp) α titanium and the body-centered cubic (bcc) β titanium are schematically shown in the figure below with their most densely packed planes and directions highlighted.

The transformation temperature from one phase to another can be raised or lowered depending on the type and amount of impurities. The presence of impurities in CP titanium divides the single temperature for equilibrium transformation into two temperatures: the α transus temperature, below which the alloy is all-alpha; and beta transus temperature, above which the alloy is all-beta. Between these temperatures, both alpha and beta are present.

ASTM
Designationα Transus
°C [°F]β Transus
°C [°F] Grade 1880 [1620]888 [1630] Grade 2890 [1635]913 [1675] Grade 3900 [1650]920 [1685] Grade 4905 [1660]950 [1740] * The typical alpha and beta transus temperatures for ASTM Grade 1, 2, 3, 4 of commercially pure titanium, respectively.

Standards & Product Forms

* The typical alpha and beta transus temperatures for ASTM Grade 1, 2, 3, 4 of commercially pure titanium, respectively.

StandardProduct Form ASTM B265plate, sheet, strip ASTM B348bar, billet ASTM B367casting ASTM B381forging ASTM F467bolt, stud, screw ASTM F468nut ASTM B363BW fitting ASTM B861seamless pipe ASTM B862welded pipe ASTM B338smls & wld tube *ASTM standards and products forms for commercially pure titanium.

Chemical Composition Requirements

*ASTM standards and products forms for commercially pure titanium.

ElementASTM Grade 1
wt. %ASTM Grade 2
wt. % C≤0.10≤0.10 H≤0.015≤0.015 O≤0.18≤0.25 N≤0.03≤0.03 Fe≤0.20≤0.30 Tibalancebalance *Chemical requirements for ASTM CP titanium Grade 1 (UNS R50250) and Grade 2 (UNS R50400).

*Chemical requirements for ASTM CP titanium Grade 1 (UNS R50250) and Grade 2 (UNS R50400).

ElementASTM Grade 3
wt. %ASTM Grade 4
wt. % C≤0.10≤0.10 H≤0.015≤0.015 O≤0.35≤0.40 N≤0.05≤0.05 Fe≤0.30≤0.50 O.T.≤0.400.40 Tibalancebalance *Chemical requirements for ASTM CP titanium Grade 3 (UNS R50550) and ASTM titanium Grade 4 (UNS R50700).

Mechanical Properties

*Chemical requirements for ASTM CP titanium Grade 3 (UNS R50550) and ASTM titanium Grade 4 (UNS R50700).

ASTM
DesignationTensile Strength
min. MPa [ksi]Yield Strength
MPa [ksi]Elongation
min. % Grade 1240 [35]170-310 [25-45]24 Grade 2345 [50]275-450 [40-65]20 Grade 3440 [64]380-550 [55-80]18 Grade 4550 [80]480-655 [70-95]18 *Tensile requirements for CP titanium ASTM Grade 1, 2, 3, 4, respectively.

*Tensile requirements for CP titanium ASTM Grade 1, 2, 3, 4, respectively.