Microstructure and properties of Cu-bearing carbidic austempered ductile iron

Abstract In this paper, the effects of copper addition (0–2.0 wt.%) on the microstructure and properties of carbidic austempered ductile iron were studied using an optical microscope, a scanning electron microscope, a Rockwell hardness tester, a pendulum impact tester, an X-ray diffractometer, a block-on-ring wear testing machine and an electrochemical tester. The amount of carbides and graphite nodules simultaneously decreased with the increase in Cu content. Cu also improved the nodularity of graphite, made the graphite nodules grow, increased the pearlite content and refined the pearlite. After austenitizing (900°C / 100 min) and austempering (300°C / 100 min), the amount and size of the acicular ferrite significantly reduced with the addition of Cu. In contrast, the amount of retained austenite dramatically increased, and the carbon content in retained austenite slightly increased. The hardness of carbidic austempered ductile iron had no obvious change with the increase in Cu content. The wear resistance of carbidic austempered ductile iron first increased and subsequently decreased, and the impact toughness and corrosion resistance were improved with the increase in Cu content. The comprehensive properties of carbidic austempered ductile iron were optimal, with the Cu content of 1.0 wt.%.