SAE 4330 Steel
SAE 4330 is a nickel-chromium-molybdenum-vanadium alloy steel (1.65–2.00% Ni, 0.70–0.90% Cr, 0.35–0.45% Mo, 0.03–0.10% V) that represents a significant step up in fracture toughness over the simpler Cr-Mo 41xx grades at comparable strength levels. The nickel and vanadium additions refine the grain structure, inhibit grain growth during heat treatment, and substantially improve low-temperature impact resistance. Tensile strengths of 180,000–220,000 psi are routinely achieved.
The vanadium-modified composition governed by AMS 6411 — sometimes designated 4330V or 4330 Modified — is the standard aerospace form of this alloy. It is the primary specification for aircraft structural forgings, actuator bodies, and landing gear components where the combination of high strength and fracture toughness is mandatory for damage-tolerant design compliance.
Product Forms & Size Range of SAE 4330 Steel
SAE 4330 bar and forging stock per AMS 6411 is available in round bar diameters from 0.750 inch to 12.000 inches and as billet for forging. Bar is supplied in the annealed or normalized condition. Vacuum arc remelt (VAR) grades are available for applications requiring maximum fracture toughness and fatigue resistance, particularly in large-section landing gear forgings.
Mechanical tubing in SAE 4330 is produced per AMS 6411 in outside diameters and wall thicknesses per customer specification. Tubing is used for actuator cylinders, structural hollow shafts, and hydraulic system bodies in critical aerospace and defense systems where light weight and high strength are simultaneously required.
HEAT TREATMENT OF SAE 4330 STEEL
Austenitize at 1550–1600°F (843–871°C), oil quench, and double temper at 300–600°F (149–316°C) for maximum strength applications such as landing gear, or at 700–1000°F (371–538°C) for higher toughness structural applications. Double tempering is standard to ensure complete transformation of any retained austenite and full stress relief of the martensite. AMS 6411 specifies a minimum tensile strength of 180,000 psi in the heat treated condition.
4340 Air Melt Steel
Classic aerospace Ni-Cr-Mo structural steel achieving 200–260 ksi — the most specified high-strength alloy steel for aircraft primary structure.
4335 Steel
Higher-nickel Ni-Cr-Mo alloy offering improved hardenability and toughness for large-section aerospace structural forgings.
Certified Material for Critical Service
SAE 4330 steel is supplied to AMS 6411 (bars, forgings, and mechanical tubing). Material is certified to chemical composition, mechanical properties, and cleanliness per AMS 2301 or AMS 2303 depending on the quality level specified. VAR and VIM-VAR melt practice is available for the most demanding applications.