AISI 4140 is a through-hardening chromium-molybdenum medium carbon steel. It is not subject to temper embrittlement. It is recommended for heavy duty service. 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-18. Producer or source: Alloy steel mills and foundries. Originally published May 1954, revised September 1988.