Austenitizing and austempering kinetics in thin-walled ductile iron castings

摘要

This study presents some possibilities of producing thin-walled ductile iron castings with an ausferritic matrix. The research was conducted on thin-walled iron castings with 2 mm thick walls and characterized by a nodule count of 1992 mm~(-2). In this work, a reference casting was considered with 25 mm thick walls and a nodule count of 330 mm~(-2). An austenitizing temperature of 920°C was and an austempering temperature range of 300 - 400°C were considered. The austenitizing and austempering transformation rate were determined by dilatometric means. The experimental outcome was then confirmed by microstructural evaluations. It was found that the austenitizing time needed for austempering in thin-walled iron castings reduces by more than three times when compared with that corresponding to conventional castings. In addition to the the cast structure, the cast iron mechanical properties such as ultimate tensile strength, elongation and hardness were also measured. The results of this research indicate that it is possible to produce thin-walled castings for all ASTM 897M grades of ausferritic ductile iron.