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.

Duplex Steel: Strength & Corrosion Resistance Beyond 316
316 Stainless steel fasteners have many applications, but if you are looking for an all-around improved fastener without breaking the budget, Duplex alloys might be a good choice. Duplex steel fasteners are known for their improved strength (being about 2x stronger) and have significantly improved corrosion resistance compared to 316 stainless steel.  This newsletter highlights the difference between Duplex 2205 and Super Duplex 2507 fasteners; and when you may want to upgrade from a 316 stainless steel.

Why Choose Duplex Alloy over 316 Stainless?
You should consider a Duplex steel alloy bolt when the limits of 316 fasteners are reached from both a mechanical and corrosion resistance perspective. Both of these alloys: Duplex 2205 (S32205) and Super Duplex 2507 (S32750) have typically 2X the yield strength of 316. Additionally, both alloys are significantly more corrosion resistant than 316 stainless fasteners; with the Super Duplex alloy being the more resistant of the two.

Additional Duplex Offerings: Zeron 100
Before moving up to nickel alloys, Extreme Bolt also offers Zeron 100 fasteners (also known as F55 or UNS S32760) which is a variant of Super Duplex 2507 for even further improved corrosion resistance.

Availability
Many common sizes of Duplex 2205 and Super Duplex 2507 fasteners are in stock and are available in standard (inch), metric and custom fasteners designs. Typically, fasteners that are not in stock can be made in about 2-4 weeks.