2205 is the benchmark duplex stainless steel — the grade every other duplex alloy on this site gets compared against. Its name is shorthand for its composition: roughly 22% chromium and 5% nickel, backed by about 3% molybdenum and 0.14-0.20% nitrogen. Those four elements are balanced specifically to split the solidified microstructure into close to equal parts austenite and ferrite. That dual-phase structure is the source of everything that makes duplex stainless distinct from the standard 300-series: the austenite islands provide ductility and toughness, while the continuous ferrite network resists chloride stress-corrosion cracking and pitting far better than an all-austenitic structure, and pushes yield strength to roughly double that of 304 or 316 in the annealed condition.

With a PREN (pitting resistance equivalent number) in the mid-30s, 2205 comfortably outperforms 316L in chloride-rich environments while costing meaningfully less than the super duplex grades that push PREN into the 40s. That balance of strength, corrosion resistance, and cost is why 2205 dominates real-world duplex use: offshore platforms and subsea equipment, pressure vessels, pulp and paper processing, desalination plants, and chemical tankers all lean on 2205 as the default duplex specification, reserving super duplex grades for the most aggressive chloride or acidic conditions.

2205's dual-phase structure is the whole story behind its machining behavior. The austenite half of the microstructure work-hardens the same way 304 or 316 does, but nowhere near as aggressively, since it only makes up about half the material instead of all of it. The ferrite half doesn't work-harden much at all — but it's noticeably harder and stiffer than austenite, and it's what makes 2205 a genuinely demanding material to cut. The net effect is a material that generates higher cutting forces and more heat at the tool edge than any standard austenitic stainless, even though it's less prone to the classic 300-series problem of a hardened skin building up under a dull tool.

Because both phases have to be sheared cleanly on every pass, tool rigidity and edge support matter as much as sharpness. A tough, wear-resistant coated carbide grade generally beats a fine-edged, aggressive geometry on 2205 — the priority is surviving sustained mechanical load and heat rather than minimizing work hardening. Coolant is important for pulling heat out of the cutting zone, since 2205's thermal conductivity is lower than carbon steel and only moderately better than 316L. Chip control tends to be more predictable than on fully austenitic grades because the ferrite content shortens the chip, but a rigid, low-deflection setup remains the single biggest factor in getting consistent tool life on this alloy.