Aircraft Alloy Steel AISI 4340 / E-4340

Technical Data Sheet


Chemical Composition Limits
Weight% C Mn P & S Si Cr Ni Mo
E4340 Bar 0.38 - 0.43 0.65 - 0.85 0.025 0.15-0.30 0.70-0.90 1.65-2.00 0.20-0.30
E4340 Plate 0.38-0.43 0.60-0.80 0.025 0.15-0.35 0.70-0.90 1.65-2.00 0.20-0.30

Alloy E 4340 is a widely used deep-hardening constructional steel. Due to E-4340's high alloy content it obtains a uniformed hardness by heat treatment. The high fatigue strength makes E4340 ideal for highly stress parts as it maintains it's strength and hardness at elevated temperatures.

Typical Mechanical Properties


Alloy Condition Tensile Strength ksi Yield Strength ksi Elongation 4D % Reduction of Area % Hardness HB
Alloy Steel E4340 Bar Annealed - - - - 235 max
Alloy Steel E4340 Bar Hardened and Tempered 260 217 10 30 -

Heat Treatment
To obtain the highest strength (260,000 psi minimum ultimate)

E 4340
Normalised 1650°F / 1 hr
Austenitise 1500°F / 1 hr
Quench Oil
Double Temper 475°F / 2 hr twice

Alloy E-4340 (4340) is available in Bar, Square, Round, Hexagon, Flat, Plates, Forging Stock and Welding Wire.  For all stock availability contact Sales.

UNS G43406
AMS 6359 Sheet / strip / plate
AMS 6409 Bars / Forgings N&T
AMS 6414 Vac Melt Bars / Forgings
AMS 6415 Bars / Forgings
AMS 6484 Bars / Forgings N&T
MIL-S-8844 Cl1
AISI E4340
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Every effort is made to ensure that technical specifications are accurate. However, technical specifications included herein should be used as a guideline only. All specifications are subject to change without notice.