4130

4130, officially AISI 4130, is a low-alloy chromium-molybdenum steel (chromoly) in the SAE/AISI 41xx family. It typically contains about 0.30% carbon, 0.80–1.10% chromium, and 0.15–0.30% molybdenum, with small amounts of manganese and silicon. This composition provides a balance of strength, toughness, and hardenability that is widely valued in structural and engineering applications.

The alloy can be heat treated by processes such as normalization, quenching and tempering, to achieve a range of hardness and mechanical properties. In the annealed condition it is relatively ductile; when hardened it offers high tensile strength and good wear resistance. It also has good weldability compared with higher-carbon steels, provided hydrogen cracking is controlled and post-weld heat treatment is used if necessary.

Common uses include aerospace components, automotive parts, and, especially in hobby and professional markets, bicycle frames and tubing. It is often supplied as bars, tubes, or plates and is marketed as chromoly steel. In tubing form it provides favorable strength-to-weight for frame builders and is favored for its fatigue resistance and ability to be shaped and welded.

Corrosion resistance is modest, so protective coatings are often employed. The term chromoly is widely used in industry to refer to 4130 and related steels.