F55 is the ASTM forging and fitting designation (A182 Grade F55) for UNS S32760, a super duplex chemistry best known under the trade name Zeron 100. Like F51 is to 2205, F55 is not a separate alloy from S32760 — it's the same composition supplied as forgings, flanges, and fittings rather than plate or tube. What makes this specific super duplex chemistry distinctive is a combination most duplex grades don't carry together: roughly 25% chromium and 3.5% molybdenum typical of super duplex, plus small but deliberate additions of copper (0.5-1.0%) and tungsten (0.5-1.0%) that push corrosion resistance further than chromium and molybdenum alone would.

That combination gives F55 a PREN comfortably above 40 — among the highest of any duplex grade in general commercial use — along with the roughly 50/50 austenite-ferrite structure and doubled yield strength common to every duplex alloy. The tungsten addition in particular improves pitting resistance in hot, acidic chloride environments beyond what a molybdenum-only super duplex like 255 achieves. F55 forgings and fittings show up in the most demanding oil and gas, subsea, and marine applications: deepwater wellhead components, seawater injection systems, and chemical processing equipment where even standard duplex or 316L doesn't provide enough corrosion margin.

F55 is the most demanding material on this page, and it earns that distinction honestly — it carries the highest alloy content of any duplex grade covered here, and every one of those alloying additions (chromium, molybdenum, nickel, tungsten) raises the strength and abrasiveness of the ferrite phase the tool has to cut through. Cutting forces and heat generation both run well above standard duplex, and tool life at aggressive parameters can fall off quickly if speeds and feeds aren't dialed back to match the alloy's mechanical strength.

As with other duplex grades, work hardening from a rubbing edge is a smaller factor than it is on 316, but that's cold comfort when the base material itself resists shearing this strongly. The priority on F55 is edge survival: a tough substrate with a wear- and heat-resistant coating, generous edge preparation, and cutting parameters set conservatively rather than pushed toward what a standard duplex grade would tolerate. Machine and workholding rigidity matter more here than almost any other material on this site — any chatter or deflection accelerates both flank wear and the risk of catastrophic edge chipping. Reduced depths of cut, moderate feeds, strong coolant delivery, and a grade specifically rated for super duplex stainless are the baseline requirements, not optional refinements.