The inside of the copper tube is in contact with the high-temperature molten steel, resulting in a large temperature difference between the inner and outer surfaces of the copper tube, high thermal stress and variability. The shape of the inner cavity of the copper tube is very important. Only when the shape of the inner cavity of the protective copper tube is consistent with the shape of the crystalline solidified shell can the air gap be small and uniform.
Therefore, the copper tube material is required to have strong resistance to thermal deformation, that is, high crystallization temperature, small thermal expansion coefficient, good thermal conductivity, and high thermal fatigue strength.
The selection of copper tube materials develops in the direction of red copper → phosphorus deoxidized copper → silver copper → chromium zirconium copper.
Since the recrystallization temperature of chromium zirconium copper is the highest among the above materials, it has the strongest thermal deformation resistance.