Q: How does a Duplex screw compare to a stainless steel 300 series fastener? Would they be better in a saltwater environment?
A: A Duplex stainless steel screw offers many advantages over 300 series stainless steel. Duplex is offered primarily in two grades Duplex 2205 and Super Duplex 2507 (with a bunch of similar varieties). Both offer good protection over salt air, brackish water and saltwater environments – a definite improvement in corrosion resistance compared to 300 stainless. In terms of strength, they are also much stronger. Duplex 2205 bolts provide a typical UTS of 110ksi and a yield strength of 80ksi, whereas Super Duplex bolts offer slightly higher strength at 125ksi UTS and 82ksi yield and a boost in corrosion resistance. This is nearly twice the strength of steels like 304 and 316.