300M Alloy Steel: AMS6257, AMS6419

The key modifications that separate 300M from standard 4340 are a higher silicon content (approximately 1.45-1.80%) and the addition of vanadium. Silicon significantly improves the alloy's resistance to low-cycle fatigue and temper softening, while vanadium refines the grain structure and enhances hardenability. The result is a steel that maintains toughness and ductility at tensile strengths exceeding 280 ksi, levels where conventional 4340 would exhibit unacceptable brittleness.

300M is produced exclusively as a consumable electrode vacuum remelted (CEVAR) product to AMS 2300 aircraft-quality cleanliness standards. This melting practice ensures extremely low non-metallic inclusion content, providing outstanding transverse ductility, impact strength, and suitability for magnetic particle inspection of finished components.

300M alloy steel is used in aircraft landing gear, flap tracks, slat tracks, structural fittings, actuator housings, and other primary structure components on both commercial and military aircraft. The alloy's ability to maintain fracture toughness at ultra-high strength levels has made it the preferred replacement for 4340 in the most demanding airframe applications. Outside of aerospace, 300M serves in racing drivetrain components and oil and gas equipment subjected to extreme mechanical loading.