Structural characterization and mechanical properties of pearlite – Enhanced micro-alloyed ductile irons

Abstract

The structural characteristic and mechanical properties of ductile irons micro alloyed with lean additions of molybdenum, nickel, copper and chromium was investigated. This was aimed at assessing the potentials of the utilization of lean ferro alloy additions (which offers reduced processing and product costs) for enhancing pearlite phase proportion, which is required for improved mechanical performance of ductile irons. The ductile irons contained a maximum of 0.2% each of Mo, Ni, Cu, and Cr and were processed using a crucible furnace. They were characterized using optical microscopy and X-ray diffractometry while hardness and tensile testings were used to evaluate the mechanical properties. The results show that the micro alloyed samples contain new compound of alloying elements with iron and the base alloy phase (FeSi, α Fe). It was also observed that the micro alloy additions resulted in significant increase in pearlite proportion from 30.63% in the base alloy to as much as 59.38% in the composition containing Mo, Ni and Cu as micro addition. Increase in hardness within the range 1.4–36.5% was obtained, while tensile strength increase within the range 35.89–80.55% with the use of the micro alloying additions. Overall, the best combination of mechanical properties was achieved for the ductile irons composition containing chromium and copper, as well as the one containing molybdenum, nickel and chromium as micro alloy additions.