AISI 4130 is a form of, and is also known as, chromoly steel. Chromoly contains two main alloying metals – chromium and (.8% – 1.1%) molybdenum, hence the name Chromoly, as well as iron, carbon, and other alloying elements. This combination of chromium and molybdenum provides many additional benefits compared to mild Carbon steel making it an ideal choice for many projects.
The American Iron and Steel Institute (AISI) created designations for different types and grades of steel. They are all four number designations with the first two numbers indicating the type of material selected and the latter two numbers representing the amount of Carbon present in the Steel. Mild steel is 1030 due to its different composition yet similar amount of Carbon in each material. The major difference between the two due to the alloying elements and proper hardening procedures. The additional chromium in 4130 increases the hardenability, strength, and corrosion resistance of the steel, while the molybdenum increases the toughness of the steel. It is important to note, while the chromium increases the corrosion resistance of the metal it is not as resistant as stainless steel and should not be used in high corrosive environments.