4130 is a type of low-alloy steel that is commonly used in the aerospace, oil and gas, and automotive industries. It is characterized by its high strength, toughness, and weldability, as well as its ability to withstand high temperatures and stress. The name "4130" comes from the American Iron and Steel Institute (AISI) naming convention, which designates alloys based on their chemical composition.

In terms of composition, 4130 steel contains approximately 0.3-0.4% carbon, 0.8-1.1% chromium, 0.15-0.25% molybdenum, and 0.15-0.25% silicon. These alloying elements contribute to the material's high strength and resistance to corrosion and wear.

4130 steel can be heat treated to achieve various levels of hardness and strength, making it a versatile material for a wide range of applications. It is often used in the manufacturing of aircraft parts, structural tubing, and high-performance racing components, among other things.