The mechanical properties of AISI 4140 vary significantly based on its supply condition (the state in which the mill delivers it). The most common conditions are annealed, normalized, and quenched & tempered (QT).
| Condition | Tensile Strength (MPa) | Yield Strength (0.2% Offset, MPa) | Elongation (% in 50mm) | Reduction of Area (%) | Brinell Hardness (HB) | Charpy Impact (J)* |
|---|---|---|---|---|---|---|
| Annealed | 655 - 850 | 415 - 550 | 25 - 30 | 50 - 60 | 197 - 235 | 40 - 60 |
| Normalized | 700 - 900 | 450 - 650 | 20 - 25 | 45 - 55 | 210 - 255 | 35 - 55 |
| Q&T (Medium) | 850 - 1000 | 650 - 800 | 18 - 22 | 45 - 55 | 248 - 302 | 25 - 45 |
| Q&T (High) | 1000 - 1200 | 800 - 950 | 12 - 17 | 35 - 45 | 302 - 375 | 15 - 30 |
*Note: Impact values are highly temperature and notch-sensitive. *QT = Quenched & Tempered. Temperatures vary (e.g., Medium ~500-600°C, High ~200-400°C).*
Annealed: Heated and slowly cooled for maximum softness and machinability. Offers the best ductility and impact toughness.
Normalized: Heated above the critical temperature and air-cooled. Provides a finer, more uniform grain structure than annealing, offering a good balance of strength and toughness, often as a pre-treatment for further hardening.
Quenched & Tempered (QT): The steel is austenitized, rapidly quenched (in oil) to form martensite, and then tempered (re-heated) to the desired strength/toughness balance. This condition provides the highest strength and is often the final state for critical components.