4565 (UNS S34565, Wnr. 1.4565, marketed as Alloy 24) is grouped commercially alongside 2507 and Zeron 100 because it competes directly with super duplex grades on corrosion performance — but metallurgically it's a different animal. Where 2205, 2507, and Zeron 100 rely on a genuine two-phase austenite-ferrite microstructure, 4565 is a fully austenitic, high-nitrogen "super-austenitic" stainless steel. It reaches super-duplex-level pitting resistance not through a ferrite phase but through an unusually heavy single-phase alloy recipe: roughly 24% chromium, 17% nickel, 4.0-4.5% molybdenum, 5.5% manganese, and around 0.45% nitrogen — a nitrogen level well beyond what even 2507 carries.

That chemistry pushes 4565's pitting resistance equivalent number (PREN = %Cr + 3.3×%Mo + 16×%N) to approximately 45, among the highest PREN values on this site and on par with the true super duplex grades. Combined with excellent resistance to intergranular corrosion, high mechanical strength, and strong weldability, 4565 is specified as a substitute for duplex, high-alloy super-austenitic, or even nickel-alloy equipment in flue-gas desulfurization systems, seawater handling equipment, and chemical process industry vessels — anywhere a fully austenitic structure is preferred over a duplex grade's ferrite phase, such as thick-section welding where duplex phase-balance control gets difficult.

4565's machining behavior follows a fully austenitic stainless steel, not a duplex one — and that matters because it lacks the ferrite phase that moderates work hardening in 2205, 2507, or Zeron 100. Instead, 4565 work-hardens aggressively under a rubbing or dull tool, the same fundamental behavior seen in 316 or Nitronic 60, but from a much higher starting alloy base: roughly 24% chromium and 4.0-4.5% molybdenum both add substantial abrasive wear on the cutting edge, while the approximately 0.45% nitrogen content — the highest of any grade in this material family — drives very high work hardening rates and mechanical strength that resist the cut itself.

The practical result combines the harder edges of both machining worlds: duplex-level cutting forces and abrasive wear from the heavy chromium-molybdenum content, plus austenitic-level work hardening from the high nitrogen content and the absence of a ferrite phase to interrupt it. Sharp, positive-rake carbide that shears cleanly is essential — any hesitation or rubbing contact work-hardens the surface immediately and compounds the difficulty of every subsequent pass. A tough, wear-resistant coated grade, rigid workholding, generous coolant, and conservative feeds and speeds are the baseline for consistent tool life; this is one of the more demanding materials in the FM Carbide stainless steel line despite not being a true duplex.