AISI 4340 steel is a tough, shock resisting, oil hardening nickel-chromium-molybdenum steel. In the heat treated condition it has the highest combination of tensile and endurance strengths along with ductility. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as fracture toughness. It also includes information on high temperature performance as well as forming, heat treating, machining, and joining. Filing Code: SA-14. Producer or source: Alloy steel mills and foundries. Originally published February 1954, revised March 1965.