• ALLOY STEEL - 4340 / 36CrNiMo4 / 1.6511
  • 4340 / 36CrNiMo4 / 1.6511

4340 / 36CrNiMo4 / 1.6511

SAE 4340 Steel Mechanical Properties:

Machining is best done with this alloy in the annealed or normalized and tempered condition. It can be machined by all conventional methods. However in the high strength conditions of 200 ksi or greater the machinability is only from 25% to 10% that of the alloy in the annealed condition.

AISI 4340 Chemical  Composition:

C(%) Mn(%)  Cr(%) Mo Ni Si(%) P(%) S(%)
0.38 - 0.43 0.6 - 0.8 1.35-1.60 0.2 - 0.3 1.65 - 2 0.15 - 0.3 ≤0.035 ≤0.04
  • Introduction

  • Heat Treatment

  • Applications

  • Equivalent Grade

  • 4340 Steel Introduction:

    AISI 4340 is a heat treatable, low alloy steel containing nickel, chromium and molybdenum. It is known for its toughness and capability of developing high strength in the heat treated condition while retaining good fatigue strength.

  • Annealing:

    A full anneal may be done at 1550 F followed by controlled (furnace) cooling at a rate not faster than 50 F per hour down to 600 F. From 600 F it may be air cooled.


    The temperature for tempering depends upon the strength level desired. Before tempering the alloy should be in the heat treated or normalized & heat treated condition - see "Heat Treatment". For strength levels in the 260 - 280 ksi range temper at 450 F. For strength in the 125 - 200 ksi range temper at 950 F. Do NOT temper the alloy if it is in the 220 - 260 ksi strength range as tempering can result in degradation of impact resistance for this level of strength.


    The alloy will harden by cold working or by heat treatment -- see "Heat Treatment" and "Tempering".

  • AISI4340 Steel Applications:

    Typical applications are for structural use, such as aircraft landing gear, power transmission gears and shafts and other structural parts.

  • 4340 Alloy Steel Equivalent Grade:

    4340 1.6511 36CrNiMo4


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