AISI 9840 is a nickel-chromium-molybdenum steel very similar to AISI 4340 with lower nickel and slightly higher manganese. In the heat treated condition it has good combination of strength, fatigue resistance, toughness and wear resistance. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as fracture toughness. It also includes information on forming, heat treating, machining, and joining. Filing Code: SA-55. Producer or source: Alloy steel mills and foundries.