Estudo do comportamento à fratura de ferros fundidos nodulares austemperados.

Abstract

The austempered ductile cast iron (ADI) is a material that offers improved product performance while reducing costs and, in many applications, surpasses steel forgings, weldments, carburized steel, malleable, gray iron and aluminium components. Besides, the ADI displays remarkable mechanical properties as high tensile strength and wear resistance, beyond of excellent fracture toughness and fatigue strength. In the present work the mechanical properties and fracture toughness were investigated on unalloyed and alloyed with copper and molibdenium ADI. The unnalloyed and alloyed with 0,2% molibdenium ADI was inoculated with 0.5, 0.7 and 0.9% of FeSi75A, while 0.5% of inoculant FeSi75B was used to inoculate the alloyed with 0.0, 0.4 e 0.8% copper ADI. The tests were realized at room temperature in a MTS 810 hidraulic machine. The mechanical properties and fracture toughness of the unalloyed ADI was comparable to that of the alloyed ADI, however it was noticed a little difference in the tolerance to the crack. The alloys inoculated with FeSi75B presented nodularity bigger than those inoculated with FeSi75A, what was attributed to the largest inoculant potential of the FeSi75B. The fracture of all samples happened in a fragile mode, however presenting mixed fracture micromorphology, constituded of microdimples and cleavage or quasi-cleavage facets.