There are a few different types of steel that are commonly used for trailer frames. The most common type is high-strength low-alloy (HSLA) steel. This type of steel contains a small amount of alloying elements, such as manganese, phosphorus, sulfur, and silicon. These elements improve the strength and ductility of the steel. HSLA steel is also less likely to crack or warp than other types of steel.
Another type of steel that is sometimes used for trailer frames is hot-rolled carbon steel. This type of steel has a higher carbon content than HSLA steel, which makes it stronger and harder. However, it is also more susceptible to rust and corrosion. Hot-rolled carbon steel is typically only used for trailers that will be used in very harsh conditions or for heavy-duty applications.