4140 Steel

4140 steel is a chromium, molybdenum, manganese low alloy steel plate that is known for its toughness, high fatigue strength, and high torsional strength.


General Info About 4140 Steel

4140 steel is a low alloy steel plate that is used in many different industries.

  • Advantages/Disadvantages

    4140 steel plate has high fatigue strength, excellent toughness, and good corrosion resistance. One disadvantage to 4140 steel is the extra care that must be taken when welding it.

  • Industries

    4140 steel is used in the aerospace, oil and gas, and many other industries.

  • Applications

    4140 steel plate is often used for shafts, crankshafts, gears, collars, and machinery parts because of its toughness, abrasion and impact resistance, and high fatigue strength.

  • Machining

    4140 steel plate has good machinability in the annealed condition.

  • Welding

    4140 steel plate is weldable by all conventional methods but requires preheating beforehand.

  • Heat Treatment

    4140 is hardened by heating to 1550°F or 845°C followed by quenching in oil.

Typical Standards

TemperThickness (Metric/Imperial)
41403" - 10"36" - 96"96" - 240"

Chemical Properties

0.8 - 1.100.75 - 1.00.380 - 0.4300.15 - 0.300.15 - 0.250.0400.035Balance

Mechanical Properties

Tensile Strength655 MPa95,000 PSI
Yield Strength415 MPa60,200 PSI
Bulk Modulus140 GPa20,300 KSI
Shear Modulus80 GPa11,600 KSI
Elastic Modulus190 - 210 GPa26,557 - 30,458 KSI
Poisson's Ratio0.27 - 0.300.37 - 0.30
Elongation at Break (50mm)25.7%25.7%
Brinell Hardness197197
Machinability (set to AISI 1212 as 100 Machinable)6565

Frequently Asked Questions about 4140 Steel

  • Is 4140 a carbon steel?


    4140 steel is considered a low alloy or carbon steel. With the addition of chromium and molybdenum, it is one of the most common alloy steels. The chromium boosts corrosion resistance and the molybdenum boosts toughness.

  • Does 4140 steel rust?


    4140 steel has excellent resistance to corrosion compared to other types of steel because of its higher percentage of chromium and molybdenum. However, once the corrosion process has started, it will rust just like most steel that has undergone the same damage.

  • Can 4140 steel be welded?


    4140 steel can be welded but requires preheating beforehand because it is more crack sensitive.

  • What makes 4140 a "chromoly" steel?


    The addition of chromium and molybdenum are why 4140 is considered a “chromoly” steel.

  • What goes into the AISI 4140 designation?


    The first “4” is 4140 indicates that the steel contains molybdenum at higher levels than other steels like the 1xxx series.

    The “1” in 4140 indicates the addition of chromium at higher levels than 46xx steels.

    The “40” differentiates 4140 steel from other 41xx series steels.

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