No. 45 steel plate characteristics commonly used carbon quenched structural steel. The steel is generally cold plastic, annealing and normalizing are better than tempering, it has higher strength and better machinability, after proper heat treatment, certain toughness, plasticity and wear resistance can be obtained, and the material source is convenient. Suitable for hydrogen welding and argon arc welding, not suitable for gas welding. It is necessary to preheat before welding and stress relief annealing after welding. Normalizing can improve the cutting performance of blanks with hardness less than 160HBS. After quenching and tempering treatment, the comprehensive mechanical properties of the steel should be optimized for other medium carbon structural steels. However, the steel has low hardenability, critical quench diameter in water is 12~17mm, and cracking tendency occurs when water quenching. When the diameter is larger than 80mm, the mechanical properties are similar after tempering or normalizing, and the medium and small die parts can obtain higher strength and toughness after tempering, while the large parts should be normalized. Therefore, this steel is usually used in the state of tempering or normalizing.