Soundness of spray formed disc shape tools of hot-work steels

This paper presents metallurgical factors causing porosity in the spray formed die inserts and the corresponding solutions. High quality die inserts can be produced by spray forming if a good control of deposition parameters and the sprayed material is assured. Mechanism of the pore formation is discussed. Deoxidation of the melt at tapping for porosity reduction is found to be very difficult because it causes great variation in viscosity of the melt so that the process is difficult to control. Often the tundish nozzle is also blocked or frozen. Modification of the steel composition is found to be an effective method to improve the soundness of the deposition. Effects of different alloying elements on the soundness of the deposition are discussed. Especially influential on improving the soundness is the increased alloying of high temperature carbide-forming elements such as vanadium. A new series of hot-work steels is developed for spray forming high quality tools, which have not only improved soundness, but also longer lifetimes than the conventional hot-work steels.