The Research Of Hot Isostatic Pressing Technology Of Ductile Iron

In this paper, two kinds of ductile cast iron (imported JGS500-7LT and homemade QT500-7LT) have been heat treated by different hot isostatic pressing (HIP) process. Microstructure and mechanical properties of these materials with and without HIP process were measured.The results showed that the imported ductile cast iron with and without HIP process Show higher comprehensive performance than homemade ductile cast iron material, especially in terms of fatigue property and impact toughness. The fatigue limit of the former is 275MPa but the latter is only 150MPa. The impact absorbing energy of the former is 7J under room temperature, but the latter is only 4J. The microstructures of materials after HIP process have obviously changed. After heat treatment, various microstructures are evenly distributed. The difference of graphite nodule diameter in matrix are less than the raw material, and the size and the sphericity of graphite nodules changed unconspicuously. With the cooling rate of hot isostatic pressing reduced, the pearlite content in the matrix reduced while the ferrite content increased, but changes of graphite nodule are less. The HIP process affects the content of various microstructures and thus the mechanical properties. After hot isostatic pressing, the comprehensive performances of the material increase significantly, especially the fatigue properties and impact toughness. The fatigue properties of imported ductile iron material increased by～20% and the domestic ductile iron increased by～70% to 100%. So the domestic ductile iron treated by hot isostatic pressing on the fatigue property has a greater potential than the imported ductile iron material. And the impact toughness of imported ductile iron materials increased by over 100%, the improvement is better than the domestic ductile iron material. In addition. After treatment by hot isostatic pressing, the strength and hardness of material highly related to the content of ferrite and pearlite. When pearlite content increased, tensile strength and the hardness increased. On the contrary, tensile strength and hardness reduced, but no linear relationship existed. In a word, reasonable HIP treatment process can improve the mechanical properties of materials.