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# 12 -14 Flat Head Undercut Bi-Flex™ 300 Series Stainless Steel Bi-Metal Self-Drilling Screws ELCO


Susceptibility To Embrittlement Failures In head to head testing, Bi-Flex™ 300 fasteners and three different types of 400 series martensitic stainless, self-drilling screws were installed in identical test coupons of unplated steel and aluminum. They were then subjected to a mildly corrosive environment of 5% neutral salt spray testing per ASTM B117. At
the start of the test all samples were torqued (preloaded) to 75 in lbs. Every 24 hours the samples were inspected for torque value and retorqued to 75 in lbs. The parts were evaluated by scanning electron microscope (S.E.M.) to determine the type of fracture that had occurred. The three 400 series fasteners
showed an intergranular type failure, indicative of fracturing that occurs from hydrogen assisted stress corrosion cracking. No failures or loss of preload occurred with the Bi‑Flex fasteners

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