Carbon steel is divided into carbon structural steel, carbon tool steel and free cutting structural steel. Carbon structural steel is divided into engineering construction steel and machine manufacturing structural steel; According to the smelting method, it can be divided into open hearth steel and converter steel; According to deoxidation method, it can be divided into boiling steel (f), killed steel (z), semi killed steel (b) and special killed steel (TZ); (4) According to the carbon content, carbon steel can be divided into low carbon steel (WC ≤ 0.25%), medium carbon steel (WC 0.25% - 0.6%) and high carbon steel (WC > 0.6%).