Titanium Grade 1, Grade 2, Grade 3 and Grade 4 belong to the group "Commercially Pure Titanium" (CP-Ti).
At the microstructural level, all of these materials consist of alpha-phase titanium.
The alpha phase is a crystal structure in titanium (hexagonal close-packed, HPC), which is stable at lower temperatures. The alpha phase gives the material advantages such as corrosion resistance, toughness and formability, but the material has lower strength than some titanium alloys that contain multiple phases.
The difference between the grades lies mainly in the content of interstitial elements; small atoms that are placed in the spaces in the titanium material's crystal structure.
In addition, iron (Fe) affects the properties of the material. Among these elements, oxygen is the most important strength factor.
As the content of interstitial elements increases, the strength of titanium also increases - while the formability (ductility) decreases.
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Ultimate Tensile Strength (UTS) indicates the maximum tensile strength before fracture and is measured in megapascals (MPa).
Weight % describes the proportion of an element present in the alloy.
For example, 0.18% oxygen by weight means that the alloy contains 0.18 grams of oxygen per 100 grams of titanium.
Titanium Grade 1 contains the least amount of interstitial elements. The result is the lowest strength, but the highest toughness and formability.
Typical values are around 240 MPa UTS and 24% elongation at break.
Titanium Grade 4 is at the opposite end of the scale. With higher contents of oxygen and iron, among other things, the material achieves higher strength - up to 550 MPa UTS, but with reduced toughness and formability.
This explains a fundamental relationship in commercially pure titanium:
More interstitial elements provide higher strength but lower ductility.
The strength therefore increases systematically with the degree number:
Want to read more about titanium? Here you can read about welding titanium .
Sources: NeoNickel, ASM International, Matmatch, AZoM
