AISI 4140 is a low-alloy steel known for its strength and toughness. It contains chromium and molybdenum, which enhance its hardenability and resistance to wear. This steel is commonly used in applications requiring high strength, such as gears, axles, and shafts. The designation "AISI" stands for the American Iron and Steel Institute, which developed a classification system for steel grades. AISI 4140 can be heat-treated to improve its mechanical properties, making it suitable for various industrial applications, including automotive and aerospace components.