Simulation of feeding flow and prediction of macro porosity of SGI casting based on microstructure formation

Abstract

Based on the model of microstructure formation of spheroidal graphite iron (SGI) casting which includes continuous nucleation and growth of graphite nodules, carbides and austenite, a method was proposed to calculate the feeding flow during solidification processes by considering mass conservation and using Darcy's laws. The method takes into account liquid shrinkage as well as shrinkage and expansion caused by different phase formation, and can calculate the flow in liquid and mushy regions. According to calculation of the flow, macro porosity formation could be described through treating free surfaces and boundary of the regions. The proposed method has been applied to an automotive wheel hub SGI casting with two different processing cases. The feeding flow during the casting solidification with two cases, especially in isolated regions, was investigated and discussed. With the flow calculation, expansion or shrinkage of liquid or mushy regions might be judged, which could offer important information for evaluating formation of macro porosity. The results of macro porosity prediction were compared with results of practical castings. It is indicated that two results were in quite good agreement, and the method could predict macro porosity formation more accurately.

Mechanism and estimation of porosity defects in ductile cast iron

“…39 Namely the D'Arcy flow is calculated with considering expansion and shrinkage of the mushy region, while this model does not reflect the porosity formation mechanism discussed above.…”

“…Further, although the computer simulation is now widely used in the industry, the porosity defects estimation 19,25,[34][35][36][37][38][39] based on those unclear formation mechanisms often fail in decreasing the defects. This paper critically reviews the formation mechanism including the estimation method and proposes a mechanism and challenges.…”

Prediction of Microstructure and Porosity Formation of Practical Spheroidal Graphite Iron Castings

“…The model of microstructure formation including pro-eutectic nodules, gray and white eutectics, and porosity prediction was established and had been in details introduced in the former publications [2][3][4]. In this paper, the model is briefly reviewed in following two sections.…”