UNS #K44220

300M VAC-ARC steel is a modified 4340 steel with added silicon allowing for use of a higher tempering temperature. The steel has high hardenability and strength with good ductility and toughness in heavy sections. It is used primarily in the 270/300ksi (1862/2068) tensile strength range for structrual aircraft applications. Vacuum arc remelting (VAR) is used to provide optimium cleanliness and preferred ingot structure.

Type Analysis

  • Carbon (Nominal) 0.42
  • Silicon (Nominal) 1.65
  • Nickel (Nominal) 1.8
  • Manganese (Nominal) 0.75
  • Chromium (Nominal) 0.8
  • Molybdenum (Nominal) 0.4
  • Iron (Nominal) Balance
  • Vanadium (Nominal) 0.07


Aircraft landing gears, flap tracks, structural applications

Applicable Specifications

  • AMS 6257 (Replaces MIL-S-8844 Class 3)
  • AMS 6417
  • AMS 6419
  • BMS 7-26 (Boeing)
  • BE1036 (Bendix)
  • CE-0896 (Bendix)
  • C-05-1190 (Lockheed)
  • DMS1935 (McDonnell-Douglas)
  • GM1012 (Grumman)
  • MIL-S-83135
  • MTL 1201 (Messier-Dowty)




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