AISI 4140 alloy steel is a medium carbon, chromium-molybdenum, through-hardening alloy steel that offers a strong combination of strength, toughness, and fatigue resistance after heat treatment. It provides good hardenability and performs well in medium to high-stress environments, making it a versatile choice for applications requiring reliable mechanical performance. In addition, 4140 can be readily nitrided to enhance surface hardness and wear resistance, improving performance in components subject to friction and surface degradation.
For machining, 4140 is often used in the annealed condition to improve machinability; however, when minimal machining is required or dimensional stability during heat treatment is critical, it is commonly supplied in the quenched and tempered condition. While not intended for the most extreme loading conditions where higher alloy steels like 4340 may be required, 4140 provides an excellent balance of strength, machinability, and durability for medium-duty applications. Typical uses include sprockets, bolts, chain pins, drill collars, universal joints, and other highly stressed components requiring consistent performance and resistance to cyclic loading.
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Read a comparison of 4340 vs 4140.
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AISI 4140 Chemical Composition
Chemical Composition (wt%) limits of AISI 4140 per ASTM A29*
| Carbon | 0.38-0.43 | Molybdenum | 0.15-0.25 |
| Manganese | 0.75-1.00 | Phosphorus | 0.035 |
| Silicon | 0.15-0.35 | Sulfur | 0.040 |
| Chromium | 0.80-1.10 |
*Maximum, unless range is indicated
AISI 4140 Physical Properties
| Density, lb/in3 | 0.284 |
| Modulus of Elasticity, psi | 29 x 106 |
| Coefficient of Thermal Expansion, 68-212˚F, /˚F | 6.83 x 10-6 |
| Thermal Conductivity, Btu/ft hr ˚F | 30.0 |
| Specific Heat, Btu/lb ˚F | 0.114 |
| Electrical Resistivity, Microhm-in | 6.42 |
AISI 4140 Standards
| ASTM A29 |
| ASTM A322 |
Your Source for AISI 4140 Alloy Steel
At Double Eagle Alloys, we supply 4140 alloy steel in long bar engineered for these demanding services. Contact our team to learn how 4140 alloy steel can support long-term performance and reliability.
Questions? We’d love to help. Contact us today to discuss your needs or to check current availability.
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Data shown are typical and provided for informational purposes only. Values should not be considered minimums or maximums for specification or final design. Actual product data may vary, and information may be revised without notice.