What is Grade 4340?

AISI 4340 is a nickel-chromium-molybdenum alloy steel. It provides the highest toughness and fatigue strength among standard alloy grades. The alloy contains nickel (1.65-2.00%), chromium (0.70-0.90%), and molybdenum (0.20-0.30%). This combination delivers exceptional hardenability and impact resistance. The 4340 steel tube achieves excellent strength at both high and low temperatures. It also maintains good ductility. This aerospace-grade material is for applications where failure is not acceptable.

AISI 4340 Tubes Specification

The following specifications define the dimensional and manufacturing parameters for AISI 4340 seamless mechanical tubing as per ASTM A519:

Specification ASTM A519 / ASME SA519
Thickness 3 - 12 millimeter, Cut to length
Schedule Thickness Ranges SCH XS, SCH 40, SCH 80S, SCH 5, SCH 80, SCH XXS, SCH 160, SCH 10, All Schedules
Tolerance Cold rolled tube: +/-0.05 millimetre
Cold drawn tube: +/-0.1 millimetre
Form Hydraulic, Square, Rectangular, Round Etc.
Sizes 1/2" NB to 36" NB
End Beveled, Threaded, Plain
Type Welded | CDW | ERW | DOM | Seamless | Fabricated | CEW | LSAW
Surface Finish 2B, No.1, No.4, No.8 Mirror Finish
Length Single and Double Random, Cut to Length
Delivery Condition Annealed & Pickled, Polished, Bright & Annealed, etc.

ASTM A519 GRADE 4340 Tube Chemical Composition

AISI 4340 features a carefully balanced nickel-chromium-molybdenum alloy composition designed for superior strength and toughness. The chemical composition is detailed in the table below:

C Mn P S Si Ni Cr Mo
0.38-0.43 0.60-0.80 0.035 0.040 0.15-0.35 1.65-2.00 0.70-0.90 0.20-0.30

ASTM A519 GRADE 4340 Tube Mechanical Properties

AISI 4340 mechanical properties vary with heat treatment conditions. The mechanical properties are given in the table below.

  Normalized Annealed
Tensile Strength 185,500 psi 108,000 psi
Yield Strength 125,000 psi 68,500 psi
Elongation (2") 12.2% 22%
Reduction in Area 36.3% 49.9%
Brinell Hardness 363 217

ASTM A519 GRADE 4340 Tube Equivalent Grades

The following table presents AISI 4340 steel tube equivalents across major international standards:

Standard ASTM A519 EN 10297 BS 3059 JIS G3441
Grades 4340 36CrNiMo4/
1.6511		 EN24/817M40 SNCM 439/SNCM8

4340 Steel Tubes Melting Point

The melting point of 4340 alloy steel is approximately 1427-1510°C (2600-2750°F).

Applications

4340 tube applications demand the highest levels of strength, toughness, and fatigue resistance. This tube is used in the following 4 applications:

Aircraft Landing Gear Components

Landing gear assemblies need grade 4340 for its combination of high strength and impact toughness. These critical structural components must handle severe loading during takeoff and landing. Safe aircraft operation depends on this reliability.

Forged Hydraulic Equipment

Racing and extreme-duty hydraulic components use this tube for a reason. The material withstands high pressures. It handles cyclic loading without fatigue failure. This makes it a preferred choice for applications where performance matters.

High-Strength Forged Steel Crankshafts

Performance engine crankshafts use a 4340 steel tube for its superior fatigue strength. The material handles the torsional and bending stresses of high-output applications. Racing engines and heavy machinery benefit from this capability.

Power Transmission Gears and Shafts

Heavy-duty gears, shafts, and couplings in industrial machinery rely on 4340 tube. The wear resistance and core toughness make it suitable for reliable power transmission. Automotive drivetrains also use this grade for demanding applications.