← All grades

AISI 4340

SAE 4340 · AISI/SAE

EngineeringAISI Ni Cr Mo

AISI 4340 (SAE 4340) is an engineering steel (Ni-Cr-Mo family) to AISI/SAE. It has a specified 0.2 % proof stress of 470 MPa and a typical tensile strength of about 745 MPa, with a uniform elongation of 22 %. Nominal carbon content is around 0.38 %. For nonlinear FEA, a bilinear model uses E = 210 GPa up to yield and a tangent modulus of 1275 MPa above it. It is a general-purpose wrought steel selected on strength, cost and availability.

0.2% proof Rp0.2
470MPa
UTS Rm (typ)
745MPa
Uniform elong. εu
22.0%
Condition / basis
N

Bilinear material model — nonlinear FEA

Elastic modulus E
210GPa
0.2% proof Rp0.2
470MPa
UTS Rm (typ)
745MPa
Tangent modulus Et
1275MPa

Uniform elongation εu = 22.0% · conservative analysis limit ½εu = 11.0%

Bilinear (BISO) approximation. Elastic modulus E up to the 0.2% proof stress R_p0.2, then a single tangent slope Eₜ to the ultimate tensile strength: Eₜ = (Rₘ − R_p0.2) / (εu − R_p0.2/E − 0.002), where εu is the uniform elongation and Rₘ is a typical (nominal) UTS within the specified band. The half-εu figure is a conservative strain limit for the analysis. Treat these as guidance for first-pass models; for critical work use a measured true stress–strain curve for the actual product and condition.

Ratings — engineering judgement

Weldabilitypoor

Higher carbon (~0.38%) raises the risk of HAZ cracking — preheat and PWHT are usually required, if welding is advisable at all.

Machinabilitygood

Machines well, particularly in the normalised or pre-tempered condition.

Corrosion resistancepoor

No inherent corrosion resistance — protect by paint, galvanising or plating in exposed use.

Hardenabilitygood

Responds well to quench-and-temper (and, for the case-hardening/nitriding grades, to surface treatment).

Toughnessmoderate

Adequate toughness for general use at ambient temperature.

Indicative ratings derived from composition and family — engineering guidance, not specification values.

Physical properties

Density7850kg/m³
Elastic modulus210GPa
Shear modulus80.8GPa
Poisson's ratio0.30
Thermal expansion12.0×10⁻⁶/°C
Thermal conductivity48W/(m·K)
Specific heat470J/(kg·K)
MagneticYes

Typical values for aisi ni-cr-mo steel — use the mill certificate for the specific product.

Chemical composition (wt %)

C
0.38–0.43
Mn
0.60–0.80
Cr
0.70–0.90
Ni
1.65–2.00
Mo
0.20–0.30

Nominal composition per AISI/SAE for AISI 4340 — confirm exact limits against the standard.

Available forms

barexcellent
round, flat, square, hex
Primary form, black or bright/pre-treated.
forginggood
open- & closed-die
Commonly forged for shafts and gears.
tubemoderate
seamless
Available to order.

Common applications

  • Shafts, axles and spindles
  • Gears, pinions and couplings
  • Connecting rods and levers
  • General machined components and fasteners

History

The alloy engineering steels add chromium, nickel and molybdenum for deep hardenability and a high strength-to-toughness balance — the shafts-gears-and-bolts steels. They grew from early-1900s automotive and aircraft demand and were unified across Europe by EN 10083.

  1. 1910
    Ni–Cr and Cr–Mo alloy steels adopted for automotive and aircraft parts
  2. 1942
    BS 970 defines the EN-series alloy steels (EN19, EN24, EN36…)
  3. 1991
    EN 10083-3 harmonises the alloy quench-and-temper grades

This profile is generated from the grade's core data and family. Composition is decoded from the designation where its naming system defines it; physical properties are family-typical and ratings are indicative. Confirm critical values against the governing standard or the mill certificate. Equivalents, historical designations and hand-written expert notes are added per grade over time.