Grade 2 and Grade 3 are both classified as commercially pure (unalloyed) titanium according to ASTM B265 and other international standards. They share the same basic nature of high-purity titanium, but their chemical composition limits, especially interstitial elements, are strictly controlled at different levels. These seemingly small differences directly determine their mechanical properties, formability, and application fields. Below is a detailed comparison of their composition characteristics.
Both grades are based on Ti as the main component, with a titanium purity of above 99%. The main differences lie in interstitial elements such as oxygen, nitrogen, hydrogen, carbon, and the residual element iron. Among these, oxygen content is the most critical and representative variable.
Oxygen (O) is the most influential element in commercially pure titanium. For Grade 2, the maximum oxygen content is limited to 0.18%, while for Grade 3 it is increased to 0.25%. Oxygen acts as a solid-solution strengthener in titanium: higher oxygen content significantly improves tensile strength, yield strength, and hardness, but reduces ductility and formability. This is the fundamental reason why Grade 3 has higher strength but lower bending and stamping performance than Grade 2.
Nitrogen (N) has a similar strengthening effect to oxygen. Both Grade 2 and Grade 3 have the same nitrogen limit, with a maximum content of 0.03%. Nitrogen is also a strong strengthening element, but its content is generally low in industrial production and does not form a real difference between the two grades.
Carbon (C) is a common residual element. The maximum carbon content for both Grade 2 and Grade 3 is 0.10%. Within this range, carbon has little effect on the basic properties of pure titanium and does not contribute to the performance difference between the two grades.
Hydrogen (H) must be strictly controlled to avoid hydrogen embrittlement. Both grades have the same hydrogen limit, with a maximum of 0.015%. Low hydrogen content ensures good toughness and avoids cracking during processing or service.
Iron (Fe) is the main residual element in titanium alloys. The maximum iron content for both Grade 2 and Grade 3 is 0.30%. Iron also strengthens titanium slightly, but since the limits are identical, iron does not cause differences between the two grades.
In summary, Grade 2 and Grade 3 have almost identical chemical composition systems - the only real and meaningful difference is oxygen content. Grade 2 uses lower oxygen to maintain excellent ductility, formability, bending and stamping performance; Grade 3 increases oxygen appropriately to obtain higher strength and rigidity, while still maintaining good processability.
This controlled difference in composition makes Grade 2 suitable for parts requiring deep drawing, bending, and complex forming, while Grade 3 is used in structural parts that require higher strength and certain stiffness. Understanding their composition differences helps users select the correct titanium grade for material design, production processing, and engineering applications.
