Quenching is the key to improve the index of finished steel. Iron cannot be turned into steel by quenching. Iron can only be smelted into steel after removing impurities such as sulfur and carbon contained in iron (except carbon is only a part). When the carbon content of steel reaches a certain proportion, the related performance indexes of steel can be improved by quenching. High carbon steel can be made into tool steel by quenching. This is mainly because the hardness and wear resistance of steel are greatly enhanced by quenching, and it can be used as a tool for processing other metal materials such as steel.