ASTM F837 – Mechanical & Material Properties

The mechanical requirements for ASTM F837 fasteners are tiered based on the alloy group and the specific processing method used to achieve required strength levels.

• Austenitic Alloys (Groups 1 & 2): These are available in the AF (Annealed) condition for maximum corrosion resistance, specified at 85 ksi maximum. Alternatively, CW and CW1 conditions utilize cold working to increase minimum tensile strength up to 102 ksi.
• Martensitic Alloys (Group 5): Reserved for high-strength applications, these screws undergo a hardening and tempering process (HT). This involves heating to 1800 ± 50°F for austenitization, quenching, and reheating to a minimum of 525°F to achieve a minimum tensile strength of 160 ksi.
• Testing Protocols: While hardness and tension tests may both be performed, acceptance based on tensile requirements takes precedence. Full-size axial strength testing is the decisive method for arbitration, though core hardness (Vickers or Rockwell) is utilized when full-size tensile testing cannot be accomplished.

Material selection under the ASTM F837 specification is driven by the specific environmental challenges and structural requirements the fastener will face.

• Alloy Groups: Group 1 and 2 (Austenitic) provide superior general corrosion resistance for various applications, while Group 5 (Martensitic) offers the highest mechanical strength but requires a specific hardening and tempering heat treatment to achieve its properties.
• Chemical Composition: All alloys must strictly adhere to the chemical limits defined in the specification, including precise control over elements such as Carbon, Chromium, and Nickel to ensure material integrity.
• Manufacturing Standards: Unless otherwise specified, screw heads may be hot forged, cold forged, or machined at the manufacturer's option. For fasteners up to 1.00 in. in diameter and 6 in. in length, threads are typically formed by rolling to enhance fatigue resistance.
• Passivation: To ensure the longevity of the stainless steel's protective oxide layer and maximize corrosion resistance, screws are typically cleaned, descaled, and passivated in accordance with ASTM A380 or ASTM A967.