4340 steel

4340 steel is an ultra-high strength steel classified a medium-carbon, low-alloy steel. 4340 steel has high strength, ductility, toughness, creep resistance, and fatigue resistance relative to most other steels. Hardness ranging from 24 to 53 HRC can be achieved, depending on the heat treatment.

Mechanical Properties
The mechanical properties of 4340 are highly dependent on the heat treatment. 4340 can commonly have yield strengths of 740-1860 MPa, tensile strengths of 860-1980 MPa, elongations of 11-23%, and plane strain fracture toughness of 53-110 MPa√m.

Applications of 4340 steel include heavy shafting, fasteners, aircraft, automotive, and hydraulic systems.