4340 Steel

4340 Chrome Moly Nickel Steel

AISI 4340 alloy steel is a heat treatable and low alloy steel containing chromium, nickel and molybdenum. It has high toughness and strength in the heat treated condition.

Chemical Composition
The following table shows the chemical composition of AISI 4340 alloy steel.

  • Element
  • Iron, Fe
  • Nickel, Ni
  • Chromium, Cr
  • Manganese, Mn
  • Carbon, C
  • Molybdenum, Mo
  • Silicon, Si
  • Sulfur, S
  • Phosphorous, P
  • Content (%)
  • 95.195 – 96.33
  • 1.65 – 2.00
  • 0.700 – 0.900
  • 0.600 – 0.800
  • 0.370 – 0.430
  • 0.200 – 0.300
  • 0.150 – 0.300
  • 0.0400
  • 0.0350


Fabrication and Heat Treatment

AISI 4340 alloy steel can be machined using all conventional techniques. Machining process can be performed in the annealed or normalized and tempered conditions.

AISI 4340 alloy steel has good ductility and formability in the annealed condition. It can be bent or formed by pressing or spinning in the annealed state.

AISI 4340 alloy steel can be welded using fusion or resistance welding methods. Preheat and post heat weld procedures are followed while welding this steel by established methods.

Heat Treatment
AISI 4340 alloy steel is heat treated at 830oC (1525oF) followed by quenching in oil.

This alloy steel is forged at 427 to 1233oC (1800 to 2250oF).

Cold Working
AISI 4340 alloy steel can be cold worked using all conventional methods in the annealed condition. It has high ductility.

This alloy steel is annealed at 844oC (1550oF) followed by cooling the furnace.

This alloy steel should be in the heat treated or normalized and heat treated condition before tempering. Tempering temperatures depend upon the desired strength level.

This alloy steel can be hardened by cold working or heat treatment.

This alloy steel is mainly used in power transmission gears and shafts, aircraft landing gear, and other structural parts.

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