AMS 6274
AMS 6274 is the SAE Aerospace Material Specification for SAE 8620 nickel-chromium-molybdenum carburizing alloy steel in the bar and mechanical tubing product forms. SAE 8620 (0.18–0.23% C, 0.40–0.70% Ni, 0.40–0.60% Cr, 0.15–0.25% Mo) is the most widely used carburizing steel in the aerospace industry, combining good core hardenability (providing a tough, impact-resistant core at 130,000–160,000 psi) with excellent case hardenability (providing a wear-resistant carburized case at 58–65 HRC) to produce the case/core combination required for aerospace transmission gears and shafts.
Bar and tubing to AMS 6274 is supplied in the annealed condition for machining of gear blanks, camshaft journals, and other case-hardened components. The Ni-Cr-Mo composition is particularly effective for nickel-doped carburizing processes that maximize case toughness while maintaining case hardness, and for applications requiring low-temperature impact toughness in the core at arctic operating temperatures.
SAE 8620 to AMS 6274, when gas carburized to a case depth of 0.020–0.060 inch and heat treated, produces a carburized case hardness of 58–65 HRC with core tensile strength of 130,000–160,000 psi and Charpy V-notch impact energy of 50–80 ft-lb. Full case depth and hardness uniformity is verified by Vickers microhardness traverse. Retained austenite in the case is controlled below 25% by cryogenic treatment after quenching to ensure dimensional stability in precision gear applications.
- Aerospace transmission spur, helical, and bevel gears
- Helicopter gearbox compound gear sets
- Aircraft engine camshafts and valve train components
- Aerospace drive shaft universal joint yokes
- Planetary gear carriers and sun gears
- Splined shaft and coupling components
AMS 6322 — 8740 Bar/Tube
Higher-Mo Ni-Cr-Mo alloy with greater hardenability than 8620 — for larger-section gears, shafts, and aerospace bolts.
AMS 6440 — 52100 Bearing Steel
Through-hardening bearing steel for rolling element bearings — maximum hardness and contact fatigue life at 60–66 HRC.
Certified Material for Critical Service
AMS 6274 bar certifications include chemical composition per heat, mechanical properties of core material per lot (tensile, yield, elongation, reduction of area, Charpy impact), grain size, and inclusion rating per AMS 2301. Carburizing process certification and case hardness/depth testing are performed per the applicable gear manufacturing specification and drawing requirements. Full heat-lot traceability is maintained.