Titanium is a lightweight and highly reactive transition metal valued in engineering for its unique balance of properties. To classify the material for different uses, a grading system is employed, which helps specify the chemical composition and expected mechanical performance. These grades are broadly split into unalloyed, or Commercially Pure (CP), and alloyed forms. Among the unalloyed options, Grade 2 titanium is recognized as the industry workhorse, providing the most common combination of strength, ductility, and resistance to chemical environments.
Commercially Pure Titanium: Defining Grade 2 Composition
The designation “Commercially Pure” (CP) means the material is unalloyed, consisting of at least 99% titanium, but contains controlled, trace amounts of impurities from the refinement process. These trace elements are not intentionally added as alloying agents. Their maximum allowable levels are strictly defined by specifications like the ASTM B348 standard.
The primary elements that control the mechanical properties of CP titanium are interstitial elements such as oxygen, iron, nitrogen, and carbon. Higher concentrations of these elements—especially oxygen—increase the metal’s strength but reduce its ductility and formability. Grade 2 is positioned between the softest Grade 1 and the stronger Grades 3 and 4 in terms of impurity content.
Grade 2 typically permits a maximum of 0.25% oxygen and 0.30% iron by weight. This moderate level of interstitial elements provides a good balance, making it stronger than Grade 1 while retaining a high degree of workability. This precise chemical control distinguishes the various CP grades, allowing engineers to select the best option based on required strength and ease of fabrication.
Essential Performance Characteristics and Formability
Grade 2 titanium offers a moderate strength profile, with a minimum yield strength of 275 megapascals (MPa). While lower than alloyed grades like Grade 5, it is superior to Grade 1, making it suitable for load-bearing, non-structural applications.
The material possesses a low density (approximately 4.51 g/cm³), which is less than 60% the density of many steels. This low mass combined with its moderate strength yields an excellent strength-to-weight ratio, a highly desirable trait in engineering design.
Grade 2’s exceptional corrosion resistance stems from a naturally occurring, stable titanium oxide film that forms immediately upon exposure to oxygen. This passive layer makes the metal virtually immune to attack from many common corrosive agents. It performs reliably in environments containing moist chlorides, seawater, and most oxidizing acids.
Grade 2 exhibits excellent ductility and is highly formable, earning its reputation as a preferred material for manufacturing complex shapes. It can be easily cold-formed, meaning it can be shaped without requiring high temperatures, which simplifies the manufacturing process. Furthermore, its excellent weldability allows for reliable joining using standard techniques like Gas Tungsten Arc Welding (GTAW).
Common Industrial and Consumer Applications
The outstanding corrosion resistance of Grade 2 makes it invaluable in the chemical processing industry for equipment handling aggressive fluids. Applications include heat exchangers, condensers, and reaction vessels that must withstand continuous exposure to high temperatures and corrosive agents. Its resistance to saltwater and brine also makes it a primary choice for marine and offshore environments.
In the maritime sector, Grade 2 is used in components for desalination plants, where it resists the highly corrosive effects of concentrated salt solutions. It is also found in submersible parts and ship structures where prolonged contact with seawater is unavoidable. The material’s low density is an advantage in aerospace for non-structural components like ductwork and airframe skins in areas that do not require the ultra-high strength of titanium alloys.
Grade 2’s biocompatibility allows it to be used in certain medical devices, such as surgical tools and equipment casings. While higher-strength alloys are often preferred for highly stressed orthopedic implants, Grade 2 serves well where ductility and corrosion resistance are the primary requirements. The material is also used in consumer products, like architectural cladding and jewelry, where its durability and resistance to tarnish are valued.