AISI 4140 is a versatile chromium-molybdenum alloy steel known for its high strength, toughness, and wear resistance, making it suitable for applications like gears, axles, and heavy machinery components. Its desirable properties are enhanced by the chromium and molybdenum content, which increase strength and hardenability. It is oil-hardenable and can be further treated to achieve a wide range of properties, allowing for its use in diverse industrial and automotive applications.