The annealed structure of mild steel is ferrite and a small amount of pearlite, its strength and hardness are lower, and its plasticity and toughness are better.Therefore, its cold forming property is good, can be used to roll, bending, stamping and other methods for cold forming.The steel also has good weldability.Low carbon steel with a carbon content ranging from 0.10% to 0.30% is readily acceptable for various machining processes such as forging, welding and cutting, and is often used to manufacture chains, rivets, bolts, shafts, etc.The carbon content of carbon steel is less than 1.35%(0.1-1.2%), except for iron, carbon and silicon, manganese, phosphorus, sulfur and other impurities within the limit, steel without other alloy elements.The performance of carbon steel depends mainly on its carbon content.With the increase of carbon content, the strength and hardness of steel increase, and the plasticity, toughness and weldability decrease.Compared with other types of steel, carbon steel is the earliest in use, with low cost, wide performance range and the largest consumption.It is suitable for water, steam, air, hydrogen, ammonia, nitrogen and petroleum products whose nominal pressure is pn≤ 32.0mpa and temperature is -30-425℃.Common grades include WC1, WCB, ZG25 and high quality steel 20, 25, 30 and low alloy structural steel 16Mn.The range of carbon steel should be larger, low carbon steel, medium carbon steel, high carbon steel belong to carbon steel.

Refers to less than 2.11% mass fraction of carbon and alloy elements contain no specially join steel. Sometimes referred to as the carbon steel or carbon steel. Carbon steel or carbon steel, refers to the Wc is less than 2.11% of the iron carbon alloy. The carbon content of carbon steel in addition to carbon generally contain small amounts of silicon, manganese, sulfur, phosphorus. 1) can put according to the use of carbon steel three classes of carbon structural steel, carbon tool steel and easy cutting steel, carbon structural steel engineering building is divided into structural steel two kinds of steel and machine manufacture;(2) according to the smelting method can be divided into open hearth steel, converter steel;(3) according to the method of deoxidation, it can be divided into rimmed steel (F), composed steel (Z), semi-composed steel (b) and special composed steel (TZ).(4) according to the carbon content of carbon steel can be divided into low carbon steel (WC ≤ 0.25%), medium carbon steel (wc0.25% -- 0.6%) and high carbon steel (WC>0.6%).(5) according to the quality of steel, carbon steel can be divided into ordinary carbon steel (containing phosphorus, sulfur higher), high-quality carbon steel (containing phosphorus, sulfur lower), high-grade quality steel (containing phosphorus, sulfur lower) and superior quality steel.