Nitralloy N Steel
Nitralloy N is an aluminum-chromium-molybdenum alloy steel specifically formulated for the nitriding process. The aluminum addition (0.85–1.20% Al) forms very hard aluminum nitrides in the surface layer during nitriding, producing case hardness values of 65–70 HRC — the highest surface hardness achievable in ferrous alloys without compromising core toughness. The nitrided case is formed without quenching, so dimensional distortion is minimal and the risk of quench cracking is eliminated.
Nitralloy N is governed by AMS 6470 (air melt) and AMS 6471 (VIM-VAR) for premium-cleanliness aerospace applications. Its combination of extreme surface hardness, excellent wear resistance, and good fatigue strength under bending and torsion makes it the standard material for aerospace nitrided gears, spindles, dies, and precision shafts in applications where conventional case-hardening steels are insufficient.
Product Forms & Size Range of Nitralloy N Steel
Nitralloy N bar per AMS 6470 is available in round bar diameters from 0.500″ to 10.000″, supplied quenched and tempered to 130,000–150,000 psi before nitriding. Used for gear blanks, spindles, arbors, and die bodies that are finish-machined and then gas-nitrided to final case hardness.
NITRIDING PROCESS FOR NITRALLOY N
Nitralloy N is pre-heat-treated to the required core strength before nitriding: austenitize at 1600–1650°F (871–899°C), oil quench, and double temper at 1050–1200°F (565–649°C) to develop the core properties. Nitriding is then performed at 925–975°F (496–524°C) in a dissociated ammonia atmosphere for 20–90 hours depending on the required case depth (0.010–0.025 inch effective). Post-nitriding temper at 300–400°F removes hydrogen. Final case hardness: 65–70 HRC. Core hardness: 28–35 HRC.
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Certified Material for Critical Service
Nitralloy N steel is supplied to AMS 6470 (air melt, bar and forging stock) and AMS 6471 (VIM-VAR, premium cleanliness). Certified mill test reports document chemistry (including aluminum content), core mechanical properties after pre-nitriding heat treatment, and melt practice. AMS 2759/10 governs the nitriding treatment process specification.