Delayed ausforming in high-alloy ductile cast iron, part I: tensile properties of rolled irons

摘要

A high-alloy ductile cast iron with a nominal composition of 3.76% C, 2.95% Si, 0.33% Mo, 0.42% Cu, 1.35% Ni and 0.19% Mo was cast into standard Y-blocks in green sand molds. The bottoms of the castings were selected for preparation into rectangular bars, which were subsequently austenitized and quenched in molten salt to an austempering temperature for various times penetrating the ausferrite transformation. They were then deformed by rolling to a 20% reduction in height and returned to the salt bath for the remainder of an hour at the austempering temperature. Tensile bars were then prepared from the delay-ausformed-austempered specimens. It was observed that the effect of delaying the ausforming operation was to eventually reduce the ductility of the specimens, but not until at least 10-20% ausferrite was present in the matrix microstructure before ausforming. Thus, the practical time range for ausforming could be increased, thereby increasing the feasibility for this method of processing. It is proposed that this addition of mechanical processing to the method of austempering ductile iron also has the eventual possibility of actually opening up the normal chemical (alloy content) and thermal (choice of heat treatment temperatures and times) windows of opportunity for austempered ductile iron (ADI).