Editorial Feature

AISI 4140 Alloy Steel (UNS G41400)

This article was updated on 18th December 2019

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Alloy steels are designated by AISI four-digit numbers and comprise different kinds of steels, each with a composition which exceeds the limitations of B, C, Mn, Mo, Ni, Si, Cr, and Va set for carbon steels.

AISI 4140 alloy steel is a chromium-, molybdenum-, and manganese-containing low alloy steel. It has high fatigue strength, abrasion and impact resistance, toughness, and torsional strength. The following datasheet gives an overview of AISI 4140 alloy steel.

Chemical Composition

The following table shows the chemical composition of AISI 4140 alloy steel.

Element Content (%)
Chromium, Cr 0.80 - 1.10
Manganese, Mn 0.75 - 1.0
Carbon, C 0.380 - 0.430
Silicon, Si 0.15 - 0.30
Molybdenum, Mo 0.15 - 0.25
Sulfur, S 0.040
Phosphorous, P 0.035
Iron, Fe Balance

Physical Properties

The physical properties of AISI 4140 alloy steel are highlighted in the following table.

Properties Metric Imperial
Density 7.85 g/cm3 0.284 lb/in³
Melting point 1416°C 2580°F

Mechanical Properties

The following table outlines the mechanical properties of AISI 4140 alloy steel.

Properties Metric Imperial
Tensile strength 655 MPa 95000 psi
Yield strength 415 MPa 60200 psi
Bulk modulus (typical for steel) 140 GPa 20300 ksi
Shear modulus (typical for steel) 80 GPa 11600 ksi
Elastic modulus 190-210 GPa 27557-30458 ksi
Poisson's ratio 0.27-0.30 0.27-0.30
Elongation at break (in 50 mm) 25.70% 25.70%
Hardness, Brinell 197 197
Hardness, Knoop (converted from Brinell hardness) 219 219
Hardness, Rockwell B (converted from Brinell hardness) 92 92
Hardness, Rockwell C (converted from Brinell hardness. Value below normal HRC range, for comparison purposes only) 13 13
Hardness, Vickers (converted from Brinell hardness) 207 207
Machinability (based on AISI 1212 as 100 machinability) 65 65

Thermal Properties

The thermal properties of AISI 4140 alloy steel are given in the following table.

Properties Metric Imperial
Thermal expansion coefficient (@ 0-100°C/32-212°F) 12.2 µm/m°C 6.78 µin/in°F
Thermal conductivity (@ 100°C) 42.6 W/mK 296 BTU in/hr.ft².°F

Other Designations

Other designations equivalent to AISI 4140 alloy steel are listed in the following table.

AMS 6349 ASTM A193 (B7, B7M) ASTM A506 (4140) ASTM A752 (4140)
AMS 6381 ASTM A194 (7, 7M) ASTM A513 ASTM A829
AMS 6382 ASTM A29 (4140) ASTM A513 (4140) SAE J1397 (4140)
AMS 6390 ASTM A320 (L7, L7M, L7D) ASTM A519 (4140) SAE J404 (4140)
AMS 6395 ASTM A322 (4140) ASTM A646 (4140) SAE J412 (4140)
AMS 6529 ASTM A331 (4140) ASTM A711  

Fabrication and Heat Treatment


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AISI 4140 alloy steel has good machinability in the annealed condition.


AISI 4140 alloy steel has high ductility. It can be formed using conventional techniques in the annealed condition. It requires more pressure or force for forming because it is tougher than plain carbon steels.


AISI 4140 alloy steel can be welded using all conventional techniques. However, the mechanical properties of this steel will be affected if it is welded in the heat-treated condition, and post-weld heat treatment should be performed.

Heat Treatment

AISI 4140 alloy steel is heated at 845°C (1550°F) followed by quenching in oil. Before hardening, it can be normalized by heating it at 913°C (1675°F) for a long period of time, followed by air cooling.


AISI 4140 alloy steel is forged at 926 to 1205°C (1700 to 2200°F)

Hot Working

AISI 4140 alloy steel can be hot worked at 816 to 1038°C (1500 to 1900°F)

Cold Working

AISI 4140 alloy steel can be cold worked using conventional methods in the annealed condition.


AISI 4140 alloy steel is annealed at 872°C (1600°F) followed by slowly cooling in the furnace.


AISI 4140 alloy steel can be tempered at 205 to 649°C (400 to 1200°F) depending upon the desired hardness level. The hardness of the steel can be increased if it has a lower tempering temperature. For example, a tensile strength of 225 ksi can be achieved by tempering at 316°C (600°F), and tensile strength of 130 ksi can be achieved by tempering at 538°C (1000°F).


AISI 4140 alloy steel can be hardened by cold working, or heating and quenching.


  1. Homayoun Rastan Homayoun Rastan United States says:

    What types of steel could better than AISI 4140 against torsion fatigue and shear force?

    • Shahrokh Shafiei Shahrokh Shafiei United States says:

      Hi Homyoun, what terms of use (Temperature conditions and etc )?

  2. Gary Ahlers Gary Ahlers United States says:

    Hi, I received some used track pins from a manitowik 4000 crane.  I am a blacksmith and plan to make some hammers with the steel.  I believe it is 4140.  Do you think this is a good metal for this purpose?

  3. Nicole Lecaniel Nicole Lecaniel Philippines says:

    is 4140 is same as PXA30?

    • Jimmy Jin Jimmy Jin United States says:

      PXA30 should be equivalent to P20, do you need to use P20?

  4. asem meselhy asem meselhy Egypt says:

    is it considered a good idea to manufacture gears?
    what are the suggested heat treatments to manufacture it more easily and to make the teeth endure the load and fatigue?

    • Alfredo Guerrero Alfredo Guerrero Mexico says:

      No, for gears is recommended use a steel with low carbon content to make carburizing for have a superficial case hard (wear resistant) and soft core (load and impact resistant), I recommend AISI 8620 steel

    • Dimas Silva Dimas Silva Brazil says:

      4140 is OK for big sized gears, above modulus 6. You shall then use a superficial hardening, usually with flame torch. Smaller gears, modulus below 3, for sure you should go with SAE 8620 with carburizing thickness below 20% of modulus value. After carburizing, hardening and stress relief.

  5. Subhas Nandy Subhas Nandy India says:

    Can this material be used in design of Spur Gears ? The design specifications are : Power transmitted : 5.6 kW and input speed : 1470rpm.


      that depends on your gear pcd, module, spacewidth..

  6. selwin jebadas selwin jebadas India says:

    Some one please tell me the P. No & G. No for AISI 4130 and also AISI 4140

    • Z Nipper Z Nipper United States says:

      P6 G4

  7. Hlulani Rikhotso Hlulani Rikhotso South Africa says:

    what is the best material that can be used for pressure vessels used in pneumatic vehicles.

  8. Shashidhar V Shashidhar V India says:

    What is the strength to weight ratio of AISI 4140?

  9. Muhammad Nazmi Muhammad Nazmi Malaysia says:

    Is it ok for hardness after machining for AISI 4140 to achieve 338HBW-354HBW (above client spec) and 258HBW-251HBW (below client spec) based on industry standar

  10. Moham,ed Nabil Moham,ed Nabil Egypt says:

    what are the welding electrodes specified to weld piping made from ASTM A105/A106 with pipe/tube made from AISI 4140 ?

  11. Mohamed Nabil Mohamed Nabil Egypt says:

    what are the welding electrodes specified to weld piping made from ASTM A105/A106 with pipe/tube made from AISI 4140 ?

    • Prasanna Venkatesh B Prasanna Venkatesh B India says:

      ER80SD2 OR ER80SB2 filler rod is used with TIG process for welding AISI4140 steel

  12. Tim Hogue Tim Hogue United States says:

    Can this steel be hot-dip galvanized?  I will be using it as a structural pin in an outdoor industrial environment.

  13. Nirmalendu Kuanr Nirmalendu Kuanr Canada says:

    Can someone tell me the market name of P110 steel? I asked many suppliers and they don't have it. It's kind of odd. May be I am missing the commercial/market name of P110 steel.


  14. Milind Nikam Milind Nikam India says:

    By which standard should we confirm Mechanical properties of AISI 4140?
    Cause No ASTM standard has specified Mechanical properties of Flat Bars/Rods/Forgings of AISI 4140.

    • Milind Nikam Milind Nikam India says:

      Can anyone suggest by which standard Mechanical properties of AISI 4140 to be confirmed/checked?

      • Rick Sivley Rick Sivley United States says:

        astm a193 or asme a320

  15. Rick Sivley Rick Sivley United States says:

    Can Banding in 4140 be coerected by heat treating?

  16. Jeremy P . Jeremy P . United States says:

    is 4140 annealed a grade 5 bolt spec in its natural state??

  17. htein linn aung htein linn aung Myanmar says:

    What kind of material should be used for stator and rotor of gas turbine with the revolution (48000rpm)?

  18. Siah Holder Siah Holder Trinidad and Tobago says:

    Would this be a good material for a pinion gear for use in a tidal energy harvester ?

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of AZoM.com.

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