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SAE AISI 4140 Steel Properties, Material Heat Treatment, Rockwell Hardness

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SAE AISI 4140 Alloy Steel

SAE 4140 (AISI 4140 steel) is a Cr-Mo series (Chrome molybdenum series) low alloy steel, this material has high strength and hardenability, good toughness, small deformation during quenching, high creep strength and long-lasting strength at high temperature.

4140 Steel Uses

AISI SAE 4140 alloy steel can be made into round steel bar, flat & square steel bar, steel plate, steel tube, and has many uses in the aerospace, oil and gas and automotive industries, typical uses are thin-walled pressure vessels, forged gears and shafts (Motor shafts, pump shafts, hydraulic shafts, etc.), spindles (lathe spindles, milling spindles, etc.), collars, clamps, high strength bolts, valve bonnet, screws, nuts, worms, collets, torsion bars and various carburized parts.

Datasheet & Specification

Below are 4140 alloy steel datasheets including chemical composition, properties and equivalent chart, etc.

AISI SAE 4140 Chemical Composition

The table below lists AISI 4140 chemical composition.

AISI SAE 4140 Chemical Composition (%)
Steel (UNS)CSiMnP (≤)S (≤)CrMoNi
4140 (G41400)0.38-0.430.15-0.350.75-1.000.0350.0400.80-1.100.15-0.25

AISI 4140 Steel Mechanical Properties

Material 4140 mechanical properties are given in the table below.

SteelTensile strength (Mpa)Yield strength (Mpa)Elongation in 50 mm, %Reduction in area, %Hardness (HB)Sample diameterConditions
AISI 4140102065517.746.830225.4mm (1 inch)Normalized at 870 °C
65541425.756.9197Annealed at 815 °C
107598615.556.9311Water quenched from 845 °C & tempered at 540 °C

SAE 4140 Physical Properties

Notes: 10-6/K = 10-6.K-1 = (µm/m)/°C

Material 4140 coefficients of linear thermal expansion
Temperature (°C)Value (10-6/K)Treatment or condition
20-10012.2Oil hardened, tempered
4140 thermal conductivity
Value (W/m·K)Temperature (°C)Treatment or condition
42.7100Hardened &
AISI / SAE 4140 Specific Heat
Value (J/Kg·K)Temperature (°C)Treatment or condition
47320-200Hardened &
Mateiral 4140 Electrical Resistivity
Value (μΩ· m)Temperature (°C)Treatment or condition
0.2220Hardened &

Material 4140 Steel Heat Treatment

The following table shows AISI 4140 steel heat treatment, rockwell hardness.

Material 4140 Heat TreatTemperature (℃)4140 steel hardnessCooling/Agent
Normalizing870302 HBAir
Annealing790-845197 HBFurnace cooling
Tempering (2 hour)20558 HRCOil hardening
26054 HRC
31550 HRC
37047 HRC
42545 HRC
48040 HRC
54035 HRC
59533 HRC
65028 HRC


4140 alloy steel is typically normalized at 870 °C (1600℉), and should be cooled at a specified temperature in still air.

Spheroidizing Annealing

For spheroidizing annealing of 4140 alloy steel, it needs heat treated to 749 °C (1380 °F), followed by slowly cooling to 666 °C (1230 °F) at a rate of 6 °C (10 °F)/hour, or rapid cooling to 675 °C for isothermal annealing.

Full Annealing

Heat treatment to 845 °C, slow cooling from 755 °C at a rate of 14 °C (25 °F)/hour to 665 °C, or rapid cooling to 675 °C for 5 hours isothermal annealing.


Tempering temperature of 4140 alloy steel can be from 204-649 °C (400-1200°F) after normalizing and oil quenching, and the corresponding Rockwell hardness can be obtained.


Material 4140 forging temperature is about 1232 °C (2250 °F).

Welding of 4140 Steel

All common arc welding processes, such as (SAW, SMAW, FCAW, GMAW, GTAW) can be used to weld 4140 alloy steel, but in order to prevent cracking, it must be preheated to 170-350 °C (350-650 °F) before welding, preheating interpass temperature depends on the section thickness of the steel.

Equivalent Material

AISI 4140 equivalent material is listed in the table below.

AISI 4140 equivalent
USAEuropean UnionChinaJapanISO
StandardGrade (UNS)StandardGrade (Steel Number)StandardGradeStandardGradeStandardGrade
4140 (G41400)EN 10083-342CrMo4 (1.7225)GB/T 307742CrMoJISG 4105SCM440

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1 Comment
  1. Pete Peters says


    Will BS EN 10025 S355 Steel be exactly the same as DIN EN 10025 S355 Steel for chemical composition and mechanical properties? If not, what is the purpose of an EN specification if the adopting country changes the specifications?


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