It can be known from the extrusion process that the screw works under high temperature, certain corrosion, strong wear, and high torque. Therefore, the screw must:
　

1) High temperature resistance, no deformation under high temperature; 2) Wear resistance, long life; 3) Corrosion resistance, materials are corrosive; 4) High strength, can withstand large torque and high speed; 5) Has good cutting performance ; 6) After heat treatment, the residual stress is small, the thermal deformation is small, etc.