SAE 4145 is a through-hardening, medium-carbon chromium-molybdenum alloy steel of high hardenability. It is recommended for heavy-duty service and is suitable for a wide variety of engineering uses. Its many applications include gears, axles, flanges, machine tool parts, nitrided parts, bolts, connecting rods, sprockets and valve seats. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: SA-420. Producer or source: Alloy steel mills and foundries.