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) C Si Mn P (≤) S (≤) Cr Mo Ni
4140 (G41400) 0.38-0.43 0.15-0.35 0.75-1.00 0.035 0.040 0.80-1.10 0.15-0.25

AISI 4140 Steel Mechanical Properties

Material 4140 mechanical properties are given in the table below.

Steel Tensile strength (Mpa) Yield strength (Mpa) Elongation in 50 mm, % Reduction in area, % Hardness (HB) Sample diameter Conditions
AISI 4140 1020 655 17.7 46.8 302 25.4mm (1 inch) Normalized at 870 °C
655 414 25.7 56.9 197 Annealed at 815 °C
1075 986 15.5 56.9 311 Water 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
20-100 12.2 Oil hardened, tempered
20-200 12.6
20-400 13.6
20-600 14.5
4140 thermal conductivity
Value (W/m·K) Temperature (°C) Treatment or condition
42.7 100 Hardened &
tempered
42.3 200
37.7 400
33.1 600
AISI / SAE 4140 Specific Heat
Value (J/Kg·K) Temperature (°C) Treatment or condition
473 20-200 Hardened &
tempered
519 20-400
561 20-600
Mateiral 4140 Electrical Resistivity
Value (μΩ· m) Temperature (°C) Treatment or condition
0.22 20 Hardened &
tempered
0.26 100
0.33 200
0.48 400
0.65 600

Material 4140 Steel Heat Treatment

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

Material 4140 Heat Treat Temperature (℃) 4140 steel hardness Cooling/Agent
Normalizing 870 302 HB Air
Annealing 790-845 197 HB Furnace cooling
Quenching 830-845 Oil
Tempering (2 hour) 205 58 HRC Oil hardening
260 54 HRC
315 50 HRC
370 47 HRC
425 45 HRC
480 40 HRC
540 35 HRC
595 33 HRC
650 28 HRC

Normalizing

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

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.

Forging

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
USA European Union China Japan ISO
Standard Grade (UNS) Standard Grade (Steel Number) Standard Grade Standard Grade Standard Grade
AISI SAE;
ASTM A29/A29M
4140 (G41400) EN 10083-3 42CrMo4 (1.7225) GB/T 3077 42CrMo JISG 4105 SCM440

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1 Comment
  1. Pete Peters says

    Hello,

    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?

    Thanks!

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