AISI 8640 is a nickel-chromium-molybdenum alloy steel of the oil hardening type. It has good hardenability and desirable toughness. 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 heat treating, machining, and joining. Filing Code: SA-15. Producer or source: Alloy steel mills and foundries.