ASTM F880 – Mechanical & Material Properties

ASTM F880 is the standard specification for austenitic stainless steel socket-set screws (SSS), covering sizes ranging from 0.060 in. through 0.500 in.. This specification is critical for applications requiring high corrosion resistance and specific mechanical performance in a fastener that must withstand significant torsional stress without failure. Fasteners under this standard are typically produced in two conditions: AF (Solution Annealed) and CW (Cold Worked). While AF provides maximum corrosion resistance and minimum permeability, CW is utilized when higher strength and hardness are required. To ensure compliance, the specification mandates strict controls on chemical composition, heat treatment (heating to 1900 ± 50°F), and rigorous torsional strength testing using specialized fixtures.

Mechanical Properties

The mechanical integrity of ASTM F880 set screws is primarily verified through torsional strength testing. Screws are inserted into a tapped hole of a 5H tolerance test block and subjected to the minimum torque values specified below based on their size and material condition (AF or CW). A successful test requires the screw to withstand the specified torque without evidence of socket reaming or screw bursting. Hardness limits are also defined: screws in Condition AF must maintain a hardness between 70 to 95 HRB, while Condition CW screws must meet a range of 96 HRB to 33 HRC.

Torsional Strength Requirements
Nominal Screw Size Shortest Nominal Screw Lengths Subject to Torque Testing Test Torque, in.-lb, min
Cup and Flat Points, mm Cone and Oval Points Half Dog Points, mm AF CW
#0 0.109 0.125 0.109 0.3 0.6
#1 0.125 0.141 0.125 0.7 1.2
#2 0.125 0.141 0.141 0.7 1.2
#3 0.141 0.156 0.156 1.6 3.3
#4 0.141 0.172 0.156 1.6 3.3
#5 0.188 0.188 0.172 3 5
#6 0.172 0.203 0.188 3 5
#8 0.188 0.219 0.203 9 16
#10 0.188 0.250 0.234 16 26
1/4 0.250 0.312 0.297 40 67
5/16 0.312 0.391 0.359 79 135
3/8 0.375 0.438 0.438 138 237
7/16 0.438 0.547 0.484 220 378
1/2 0.500 0.609 0.547 358 600

Material Properties

ASTM F880 utilizes various Austenitic Stainless Steel alloys, commonly within the 300-series (such as 303, 304, and 316) and specialized XM-series alloys. The choice of alloy is typically left to the manufacturer unless a specific grade is requested in the purchase order. The chemical requirements focus on maintaining high Chromium (typically 15.0%–20.0%) and Nickel (5.0%–19.0%) content to ensure the "austenitic" structure, which provides the non-magnetic properties and excellent corrosion resistance these fasteners are known for. For applications where intergranular corrosion is a concern, the specification references Practice A262 for susceptibility testing.

Chemical Composition
UNS Designation Alloy Composition, % maximum except as shown
Carbon Manganese Phosphorus Sulfur Silicon Chromium Nickel Copper Molybdenum
S30300 303 0.15 2.00 0.20 0.15 min 1.00 17.0 to 19.0 8.0 to 10.0 - 0.60 maxA
S30323 303Se 0.15 2.00 0.20 0.060 1.00 17.0 to 19.0 8.0 to 10.0 - Se 0.15 min
S30400 304 0.08 2.00 0.045 0.030 1.00 18.0 to 20.0 8.0 to 10.5 1.00 -
S30403 304L 0.030 2.00 0.045 0.030 1.00 18.0 to 20.0 8.0 to 12.0 1.00 -
S30500 305 0.12 2.00 0.045 0.030 1.00 17.0 to 19.0 10.5 to 13.0 1.00 -
S38400 384 0.08 2.00 0.045 0.030 1.00 15.0 to 17.0 17.0 to 19.0 - -
S20300 XM1 0.08 5.0 to 6.5 0.040 0.18 to 0.35 1.00 16.0 to 18.0 5.0 to 6.5 1.75 to 2.25 0.50 maxA
S30430 18—9LW 0.10 2.00 0.045 0.030 1.00 17.0 to 19.0 8.0 to 10.0 3.0 to 4.0 -
S30433 302HQ 0.03 2.00 0.045 0.030 1.00 17.0 to 19.0 8.0 to 10.0 3.0 to 4.0 -
A At the manufacturer's option, determined only when intentionally added.