Titanium Grade 4 (also known as commercially pure titanium Grade 4) is a unalloyed titanium grade, meaning its composition is dominated by pure titanium with minimal allowable impurities. The typical chemical composition (by weight), as specified in standards like ASTM B265 (for titanium plate, sheet, and strip) or ASTM B348 (for titanium bars), is as follows:
Titanium (Ti): ≥ 99.0% (the balance, with the exact percentage depending on the total content of impurities).
Carbon (C): ≤ 0.10%.
Iron (Fe): ≤ 0.50% (this is a key impurity; Grade 4 has a higher iron limit than lower-grade commercially pure titanium like Grade 1 or 2).
Oxygen (O): ≤ 0.40% (oxygen content directly influences the strength of commercially pure titanium-Grade 4 has one of the highest oxygen limits among unalloyed grades, contributing to its higher strength).
Nitrogen (N): ≤ 0.05%.
Hydrogen (H): ≤ 0.015% (strictly controlled to avoid hydrogen embrittlement).
Other elements: Each individual trace element (e.g., aluminum, vanadium) is ≤ 0.10%, and the total of all other trace elements is ≤ 0.40%.
The tensile strength of Titanium Grade 4 is one of its defining characteristics, as it is the strongest among all commercially pure titanium grades. Its tensile properties are standardized, with slight variations based on product form (e.g., plate, sheet, bar) and heat treatment state (typically annealed, the most common condition for Grade 4).
Per ASTM standards (e.g., ASTM B265, ASTM B348), the minimum tensile strength of annealed Titanium Grade 4 is 620 MPa (90 ksi, or 90,000 psi). In practical applications, the actual tensile strength often exceeds this minimum value-typical measured tensile strengths for annealed Grade 4 titanium range from 620 MPa to 795 MPa (90 ksi to 115 ksi).
It is important to note that tensile strength can be affected by factors like cold working (cold-rolled or cold-drawn products may have higher tensile strength than fully annealed ones) and product thickness (thinner sheets may exhibit slightly different strength values due to processing effects).
Yield strength (specifically 0.2% offset yield strength, the industry standard for metals) is a critical metric for Titanium Grade 4, as it indicates the stress at which the material begins to undergo permanent plastic deformation.
As per ASTM specifications (e.g., ASTM B265, ASTM B348) for annealed Titanium Grade 4, the minimum 0.2% offset yield strength is 550 MPa (80 ksi, or 80,000 psi). Similar to tensile strength, the actual yield strength of annealed Grade 4 titanium in practice often surpasses this minimum, typically ranging from 550 MPa to 725 MPa (80 ksi to 105 ksi).
Like tensile strength, yield strength is influenced by processing: cold-worked Grade 4 products (e.g., cold-finished bars) will have significantly higher yield strengths (sometimes exceeding 860 MPa / 125 ksi) due to the strain hardening effect. However, annealed Grade 4 is the most widely used form, as annealing balances strength with ductility (essential for forming and fabrication).
