AISI 4640 is an oil hardening nickel-molybdenum alloy steel having good heat treated properties, toughness and shock resistance. This datasheet provides information on composition, hardness, and tensile properties as well as fracture toughness. It also includes information on low temperature performance as well as forming, heat treating, machining, and joining. Filing Code: SA-67. Producer or source: Alloy steel mills and foundries.