Grade 3 titanium is a type of unalloyed commercially pure (CP) titanium, primarily composed of the alpha (α) phase (hexagonal close-packed structure) at room temperature. Its mechanical properties are typically specified in the annealed condition (the most common supply state), with typical values as follows:
Strength Properties
Yield Strength (0.2% offset): Approximately 370–480 MPa (54,000–70,000 psi), which is higher than Grade 1 and Grade 2 CP titanium, classifying it as a medium-strength pure titanium grade.
Tensile Strength (Ultimate): Around 480–620 MPa (70,000–90,000 psi), suitable for applications requiring moderate strength without the need for high-strength titanium alloys.
Ductility and Plasticity
Elongation at Break: 15%–25% (over a 50 mm gauge length). While lower than Grade 1 (20%–30%) and Grade 2 (20%–30%) CP titanium, it still maintains good tensile deformability, enabling forming processes like bending, stamping, and drawing.
Reduction of Area: Approximately 30%–40%, indicating excellent cross-sectional contraction capacity before fracture and balanced plastic performance.
Hardness
Brinell Hardness (HB): 110–140 HB; Rockwell Hardness (HRB): 80–95 HRB. Its moderate hardness balances wear resistance and machinability.
Low-Temperature Performance
It retains good toughness at low temperatures without significant brittle transition. Even at cryogenic temperatures (e.g., -253°C, the temperature of liquid hydrogen), it maintains acceptable ductility, making it suitable for low-temperature service applications.
Note: Specific values may vary slightly based on manufacturing processes (e.g., rolling, forging) and heat treatment parameters. For practical applications, refer to the Material Test Report (MTR) provided by the manufacturer.
Despite its utility, Grade 3 titanium has inherent limitations due to its unalloyed nature:
Lower Strength Than Titanium Alloys: Its yield strength (370–480 MPa) is significantly lower than that of alloyed titanium (e.g., Ti-6Al-4V/Grade 5, with a yield strength of ~860 MPa). This makes it unsuitable for high-load applications such as aerospace structural components or high-pressure vessels.
Poor High-Temperature Performance: Pure titanium exhibits a sharp decline in strength above 300°C, and its oxidation resistance weakens (as loose oxide films form). Thus, Grade 3 titanium is generally limited to service temperatures below 300°C and cannot be used in high-temperature environments like engine turbines or hot dies.
Inferior Corrosion Resistance to Specialized Titanium Alloys: While it performs well in most environments (e.g., seawater, dilute acids), it is less resistant to highly corrosive media (e.g., concentrated hydrochloric acid, hot nitric acid, high-concentration chloride solutions) compared to corrosion-resistant titanium alloys (e.g., Grade 2 Ti-Pd, Grade 7 Ti-0.15Pd). It is prone to pitting or crevice corrosion in such conditions.
Higher Cost Than Common Metals: The complex and energy-intensive extraction process (Kroll process) for pure titanium results in a much higher raw material cost than carbon steel or stainless steel. For cost-sensitive applications with low strength requirements (e.g., general piping, daily goods), it is less cost-effective than traditional metals.
Difficult Machinability: Titanium has a low thermal conductivity (about 1/5 that of steel), causing heat to concentrate at the tool edge during machining, leading to rapid tool wear. Additionally, titanium tends to bond with tool materials (e.g., high-speed steel) at high temperatures, requiring specialized tools and processes-reducing machining efficiency and increasing costs.
Grade 3 titanium leverages the inherent properties of pure titanium while striking a balance between strength and practicality, offering the following key advantages:
Balanced Strength and Ductility: Among CP titanium grades, Grade 3 has higher strength (370–480 MPa yield strength) than Grade 1 and Grade 2, while still retaining good ductility (15%–25% elongation). This balance allows it to meet both structural load requirements and forming needs (e.g., welding, forging, bending), making it ideal for complex-shaped components like medical device housings and chemical pipelines.
Excellent Corrosion Resistance: In natural environments (atmosphere, fresh water), marine environments (seawater, salt spray), and most industrial media (dilute sulfuric acid, dilute hydrochloric acid, organic acids), Grade 3 titanium forms a dense, stable titanium dioxide (TiO₂) passive film on its surface. This film prevents the penetration of corrosive media, giving it far superior corrosion resistance to carbon steel and stainless steel. It is widely used in marine parts, desalination equipment, and chemical storage tanks.
Superior Biocompatibility: Pure titanium is non-toxic, non-allergenic, and highly compatible with human tissues (bones, muscles), causing no immune rejection. Grade 3 titanium is therefore extensively used in medical devices, such as orthopedic implants (screws, bone plates) and dental implant abutments.
Low Density and High Specific Strength: Titanium has a density of approximately 4.51 g/cm³-only 56% that of steel and 45% that of copper. While Grade 3 titanium's specific strength (strength-to-density ratio) is lower than that of titanium alloys, it still exceeds that of carbon steel and stainless steel. This makes it suitable for lightweight applications (e.g., portable medical equipment, small marine components) where reducing structural weight is critical.
Excellent Low-Temperature Toughness: Pure titanium has no ductile-brittle transition temperature. Grade 3 titanium maintains nearly unchanged toughness over the temperature range from -253°C (liquid hydrogen temperature) to room temperature, avoiding the brittle fracture that plagues carbon steel at low temperatures. It is thus well-suited for cryogenic engineering, such as liquid gas storage tanks and low-temperature pipelines.
