AISI 4140 Steel: Properties, 42CrMo4 Equivalent, Supply

AISI 4140 (SAE 4140) is a medium-carbon chromium-molybdenum alloyed quenched and tempered steel. Because it combines high strength, good toughness, fatigue strength and hardenability, it is one of the most widely used alloy steels in the machinery, automotive, oil and gas, and defense industries. Its European equivalent is 42CrMo4 (1.7225), and its Japanese equivalent is SCM440. In this article, you will find the technical properties of 4140 material, its heat treatment behavior and the key points to consider when purchasing it.

AISI 4140 designation

In the AISI system, the 41xx group refers to chromium-molybdenum alloy steels. The last two digits, 40, indicate approximately 0.40% carbon. On the market, this steel is also known as “chromoly” or “Cr-Mo steel”.

4140 chemical composition and comparison with 42CrMo4

The chemical composition of AISI 4140 and its European equivalent 42CrMo4 are compared in the table below:

Although the two grades largely overlap, their manganese and chromium ranges are not identical. Therefore, the certificate must be issued according to whichever standard is specified on the drawing. For more information on 42CrMo4, see our article What Is 42CrMo4 (1.7225) Quenched and Tempered Steel?

Mechanical properties of 4140 steel (quenched and tempered, +QT)

Minimum values for 42CrMo4+QT by section size according to EN 10083-3:

As the table shows, the achievable strength decreases as the cross-section increases. This is due to the limited hardenability through the section. For very large cross-sections, nickel alloyed grades such as 34CrNiMo6 can be considered for higher hardenability.

Heat treatment of 4140 steel

• Soft annealing (+A): Improves machinability; hardness in the annealed condition is typically below 241 HB.
• Hardening: Quenched in oil (in water for thin sections) from approximately 820–860 °C.
• Tempering: Usually carried out in the 540–680 °C range, depending on the required hardness and toughness.
• Surface hardening: Suitable for induction or flame hardening; surface hardness of approximately 53 HRC and above can be achieved.
• Nitriding: Quenched and tempered 4140 can be nitrided to increase wear and fatigue resistance.

Exact heat treatment parameters should be determined according to section size and target properties.

Where is AISI 4140 used?

Typical applications of 4140 steel include:

• Heavily loaded transmission shafts, axles and crankshafts
• Gears, pinions and couplings
• High-strength bolts, studs and nuts
• Hydraulic cylinder rods and piston rods
• Oil and gas drilling equipment and drill collars
• Die holders and tool bodies
• Construction machinery, defense and automotive parts

AISI 4140 international equivalents

Grades equivalent to AISI 4140 in different standards are as follows:

What to consider when buying 4140 material

• Delivery condition: Annealed (+A) or quenched and tempered (+QT)? If you will not heat treat in your own workshop, choose +QT.
• Cross-section and strength: Verify that the strength targeted in the design is achievable in the relevant diameter range.
• Standard: Check whether the drawing specifies AISI 4140 or 42CrMo4, and request the certificate accordingly.
• Certification: Verify chemical analysis and mechanical test values with an EN 10204 3.1 certificate.
• Surface and tolerance: Choose between hot rolled, peeled or cold drawn options based on your machining plan.

Machinability and weldability of 4140 steel

4140 has good machinability in the annealed (+A) condition. In the quenched and tempered (+QT) condition, hardness is higher, so cutting speeds should be reduced and suitable tool coatings selected. Many workshops prefer to machine pre-hardened material to eliminate the risk of distortion from subsequent heat treatment. Weldability, however, is limited. Due to its carbon and alloy content, hard and brittle structures can form in the heat-affected zone. If welding is unavoidable, preheating, controlled interpass temperature, low-hydrogen consumables and post-weld stress relieving should be applied.

4140 or C45?

Many designers have to choose between 4140 and C45 for parts such as shafts and pins. C45 is more economical and provides sufficient strength in small cross-sections. However, as part diameter increases or impact and fatigue loads rise, the hardenability of C45 becomes insufficient. In such cases, 4140, which contains chromium and molybdenum, provides higher and more uniform strength through to the core, significantly extending part life. The decision should be made by evaluating section size, load type and cost together.

4140 / 42CrMo4 supply from Uyar Çelik

For sizes and grades with limited production in Türkiye, Uyar Çelik offers imported hot rolled alloy steel bars and forged steel bars. Through our European logistics center in Düsseldorf and our facilities in Türkiye, we reliably meet your 4140 / 42CrMo4 requirements.

Frequently asked questions

Are 4140 and 42CrMo4 the same steel?

They are largely equivalent; however, their chemical composition ranges are not identical. For critical parts, a certificate conforming to the standard specified on the drawing should be requested.

Does 4140 steel rust?

Yes. 4140 is not a stainless steel; in corrosive environments it must be protected with coating, painting or oiling.

What is the HRC hardness of 4140 steel?

After hardening, it can be adjusted over a wide range depending on the tempering temperature; in the quenched and tempered condition it is typically used at around 28–36 HRC.

Conclusion

AISI 4140 is a versatile chromium-molybdenum quenched and tempered steel that combines high strength, toughness and fatigue strength, and is considered equivalent to 42CrMo4 and SCM440. For the right choice, section size, delivery condition, the standard on the drawing and certificate values should be evaluated together. Get a quote for your AISI 4140 / 42CrMo4 steel requirements: +90 (212) 485 98 98 or visit our contact page.