Alloy steel has higher strength and toughness than carbon steel, and its reinforcement effect with the increace of tissue imbalance and tend to be more obvious, and the strength of the alloy steel annealing state than carbon steel has a lot of advantages, and in normalizing, than obviously increase the carbon steel and the strength of the alloy steel after quenching and tempering, the steel reinforcement effect is the most significant. Some alloy steels have excellent thermal hardness and other special properties, such as heat resistance, corrosion resistance, wear resistance and magnetic properties.