THE INFLUENCE OF THE GRAPHITE QUANTITY AND COMPACTNESS ON THE HOT PLASTIC DEFORMATION OF MODIFIED CAST IRON

摘要

The paper presents the results obtained from the analysis of the influence of the morphology of graphite separations on the behavior during hot plastic deformation of modified cast irons. During the investigations the torsion and upsetting tests were applied, performed under different conditions of temperature (850-950°C), deformation rale (30-400 rotations/min) and pressure (30-250 daN/cm~2). The value of the degree of deformation of ductile cast irons varies between 53.1-81%, whereas the one of the vermicular graphite cast irons varies between 39.25 - 50.25%. Microstructural investigations performed on test bars deformed by torsion and compression point out to the existence of a clear difference between the evolution of spheroidal graphite and the one of vermicular/compacted graphite during plastic deformation. The higher the degree of spheroidization and compactness of graphite is and the number of graphite separations lower, the higher is the degree of deformation of modified cast irons. The experiments and the results obtained generate the premise for the manufacture by hot plastic deformation of parts made of nodular graphite cast irons as an alternative to casting processes.