4140 and its counterparts are valued for heat-treatable strength:
ASTM A29 4140; EN 1.7225 (42CrMo4); JIS SCM440: After quenching and tempering, they achieve 850–1,100 MPa tensile strength and 700–950 MPa yield strength, with 12–18% elongation.
Key traits: Hardness up to 35 HRC (tempered) for wear resistance, combined with 25–35 J impact toughness at room temperature-ideal for high-stress components (drill collars, axle shafts).
Regional variations: 42CrMo4 has slightly higher chromium (0.90–1.20% vs. 0.80–1.10% in 4140) for better hardenability, while SCM440 includes 0.15–0.35% silicon for improved machinability.