To ensure good thermal conductivity, sufficient wear resistance, mechanical strength, and hardness of the crystallizer to extend its service life, the inner wall material is mainly made of copper based alloys, commonly used including copper, copper silver alloys (with a silver content of 0.07% to 0.1%), phosphorus deoxidized copper and copper beryllium alloys, chromium zirconium copper alloys, etc. The main purpose of using copper based alloys is to increase their recrystallization temperature, improve their hardness and strength at high temperatures, and extend the service life of the inner wall. In order to further improve the wear resistance and smoothness of the inner wall and reduce the drawing resistance, some even add a coating on the surface of the copper wall. Usually chromium plating or nickel plating, tungsten plating, iron plating, and three-layer nickel plating, nickel phosphorus alloy plating, and chromium plating.