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300M is a low alloy, vacuum melted, steel of very high strength. Essentially it is a modified AISI 4340 steel with silicon, vanadium and slightly greater carbon and molybdenum content than 4340. 300M has a very good combination of strength (280 to 305 ksi), toughness, fatigue strength and good ductility. It is a through hardening alloy.

Applications for 300M steel are those that require strength in the 290 – 300 ksi range, such as aircraft landing gear, high strength bolts, flap tracks, structural applications and airframe parts.

Chemical Properties

Element min max
Carbon 0.40 0.45
Manganese 0.60 0.90
Silicon 1.45 1.80
Phosphorus — 0.010
Sulfur — 0.010
Chromium 0.70 0.95
Nickel 1.65 2.00
Molybdenum 0.30 0.50
Vanadium 0.05 0.10
Copper — 0.35

Minimum Longitudinal Tensile Properties

Property Value
Tensile Strength 280 ksi
Yield Strength at 0.2% Offset 230 ksi
Elongation in 4D 7%
Reduction of Area 25%

Minimum Transverse Tensile Properties, Inch/Pound Units

Nominal Cross-Sectional Area Square Inches Tensile Strength ksi Yield Strength at 0.2% Offset ksi Average Reduction of Area % Individual Reduction of Area %
Up to 100, incl 280 230 30 25
Over 100 to 144, incl 280 230 25 20
Over 144 to 225, incl 280 230 20 15
Over 225 280 230 15 10