Nozzle for rolling mill as easily failure parts for high speed wire rod mill was produced with 17-4PH precipitation hardening stainless steel by investment casting.There exists many difficulties in the manufacturing process

and shrinkage porosity（hole） often occurs in the nozzle due to its complicated structure and obvious wall thickness difference.Meanwhile

crack can be easily generated at the runner location after heat treatment.Based on the structure characteristics of the nozzle parts

through optimizing mould design and making wax-pattern with paraffin-stearic acid low-point wax as well as silica sol shell molding

deformation can be effectively avoided

and dimension accuracy and surface roughness can be improved.The shrinkage porosity（hole） and thermal crack can be eliminated by optimizing gating system.Product-volumetric qualified castings were manufactured.