The Influence of Vanadium and Niobium Micro-additions on the Microstructure and Mechanical Properties of ADI

Austempered Ductile Iron (ADI) casting technology is a combination of the smelting process, its post-furnace treatment and the heat treatment of castings. Maintaining the process parameter stability of this innovative high quality cast iron with high Tensile Strength UTS and ductility properties is the aim of a number of studies on the control of graphitization inoculation and inoculation of the metal matrix. The ability to graphitise the liquid alloy decreases with its holding in the furnace, time of pouring into moulds from pouring machines. The tendency to dendritic grains crystallization and the segregation of elements such as Si, Ni and Cu decrease the ductile properties. The austenitizing process can introduce austenite grains growth negatively affecting of the ausferrite morphology. The modifying effect of small amounts of additives on the metal matrix in steel and low alloy cast steel, well known in materials engineering, has been applied to ADI. The addition of cast iron chips, Fe-V and Fe-Nb to the liquid alloy in the first inoculation is an example of a hybrid interaction. The introduction of graphitization nucleus particles and austenite crystallisation nucleus particles resulted in a stabilisation of the ductility of ADI and an increase in mechanical properties. Grains refinement of the primary austenite and precipitation hardening of ausferrite stabilise the mechanical properties of ADI. As a result of graphitization and additive structure inoculation, graphite and ausferrite morphology is improved. The obtained results point the way to further research in the field of hybrid inoculation of Ductile Cast Iron.