Grade 4 titanium is a commercially pure (CP) titanium grade, meaning it contains minimal alloying elements (unlike titanium alloys such as Grade 5 Ti-6Al-4V) and consists primarily of pure titanium (typically ≥99.0% titanium content). It is one of the most widely used CP titanium grades, distinguished by its balance of mechanical strength, corrosion resistance, and formability-though it is the strongest among all standard CP titanium grades (surpassing Grades 1, 2, and 3).
Chemically, Grade 4 titanium includes trace impurities (controlled by industry standards like ASTM B265 for plates/sheets or ASTM F67 for medical applications) such as iron (max ~0.50%), oxygen (max ~0.40%), carbon (max ~0.08%), nitrogen (max ~0.05%), and hydrogen (max ~0.015%). These impurities, particularly oxygen, contribute to its higher strength compared to lower CP grades.
Key characteristics of Grade 4 titanium include:
Excellent corrosion resistance in mild-to-moderate environments (e.g., air, fresh water, most organic acids, and dilute inorganic acids), thanks to a dense, self-healing oxide film (TiO₂) that forms on its surface.
Good formability (e.g., can be bent, rolled, welded, and machined) despite its higher strength, though it is slightly less ductile than lower CP grades (e.g., Grade 2).
Biocompatibility, making it suitable for medical implants and devices.
Its typical applications span industries like medical (orthopedic implants, surgical instruments), aerospace (non-structural components), chemical processing (low-corrosion fluid handling), and consumer goods (high-strength jewelry, watch cases).
The density of Grade 4 titanium is consistent with that of commercially pure titanium across all grades, as density is a material property primarily determined by its elemental composition (and titanium content is nearly identical in all CP grades).
The standard density of Grade 4 titanium is:
4.51 grams per cubic centimeter (g/cm³)
Or, in imperial units: approximately 0.163 pounds per cubic inch (lb/in³)
This density is significantly lower than that of common metals like steel (7.85 g/cm³) or stainless steel (7.93 g/cm³), making Grade 4 titanium a lightweight option while maintaining high strength-a key advantage for weight-sensitive applications (e.g., medical implants, aerospace components).
The hardness of Grade 4 titanium varies slightly depending on its temper (heat treatment state)-the most common temper for Grade 4 is "annealed" (a softening heat treatment that optimizes ductility and formability). Below is the typical hardness range for Grade 4 titanium in its standard annealed state, measured using common hardness scales:
Note: Hardness can increase slightly if Grade 4 titanium is subjected to cold working (e.g., rolling, forging without subsequent annealing), as cold deformation introduces internal stresses that raise strength and hardness at the cost of ductility. For example, cold-worked Grade 4 may reach Brinell hardness values up to ~130 HB, but this is less common than the annealed state for most applications.
Compared to lower CP grades, Grade 4's hardness is notably higher: for reference, annealed Grade 2 titanium typically ranges from 70–80 HB, while Grade 4's 90–110 HB range reflects its status as the strongest CP titanium grade.
