Microstructure, Mechanical, and Wear Properties of Al-Alloyed Austempered Ductile Irons

Abstract

Spheroidal graphite cast irons with 0-4 wt% aluminum addition fabricated by green sand casting were austenitized at 900 degrees C for 90 min and subsequently austempered at 300 degrees C for 60 min. The samples were subjected to dry sliding wear tests against Al2O3 balls under various conditions. Microstructural analysis showed that increasing Al decreased the acicular ferrite ratio and disrupted graphite nodularity. Accordingly, ultimate tensile strength (UTS) and hardness decreased while impact strength increased except for the 4 wt% Al-alloyed cast iron. The Al2O3 layer formed around graphite nodules could not be removed during the austempering and caused an increase in the mechanical strength of this sample. Sliding tests revealed that the wear resistance of the samples increased with sliding speed and decreased with applied load. Worn surfaces predominantly suffered from abrasion, adhesion, and delamination. Although lower Al addition increased wear losses, 4 wt% Al-alloyed cast iron showed the best wear resistance.