ASTM A449 – Mechanical & Material Properties

The mechanical properties of ASTM A449 fasteners are defined by a combination of hardness and tensile requirements, which vary according to the nominal diameter of the bolt or stud. For short fasteners—specifically bolts less than three diameters in length and studs less than four—hardness testing is the sole mechanical requirement for acceptance. For larger or longer components, full-size tensile testing is the preferred method to verify minimum tensile strength and proof load. Where full-size testing is impractical due to equipment capacity or specimen length, machined specimens are utilized to measure tensile strength, yield strength, elongation, and reduction of area. The specification establishes three primary performance tiers based on size: diameters up to 1 inch require a minimum tensile strength of 120,000 psi; those over 1 inch to 1.5 inches require 105,000 psi; and larger sizes up to 3 inches require 90,000 psi. In instances where both hardness and tension tests are performed, the tensile results take precedence for final lot acceptance.

The material integrity of ASTM A449 fasteners is predicated on controlled chemical compositions and specific steel-making processes. Steel must be produced via open-hearth, basic-oxygen, or electric-furnace methods. Type 1 fasteners utilize a medium-carbon steel chemistry, while Type 2 requires a fully killed, fine-grain steel formulated as low-carbon or medium-carbon martensite. A key chemical distinction is the requirement for a minimum of 0.0005% Boron in Type 2 heats to ensure sufficient hardenability during the quenching process. To maintain metallurgical purity and prevent embrittlement, the intentional addition of elements such as lead, bismuth, selenium, or tellurium is strictly prohibited. These chemical profiles are engineered to support the mandatory heat-treatment cycle, which involves quenching in a liquid medium followed by tempering at a minimum temperature of 800°F (425°C).