Investigating the machinability of austempered ductile irons with dual matrix structures

Abstract In this study, the machinability of austempered ductile iron with dual phase structure was investigated. Specimens were intercritically austenitized (partially austenitized) in the two phase region (α + γ) at various temperatures (810, 820 and 830 °C) for 90 min, then quenched in a salt bath held at austempering temperatures of 315 °C or 375 °C for 120 min and then air cooled to room temperature to obtain various ausferrite volume fractions and morphologies. Machinability tests were carried out at various cutting speeds (150, 180 and 210 m min−1), at a constant feed rate (0.30 mm rev−1) and depth of cut at 2 mm after austempering heat treatment. The experimental results showed that austempered specimens from the (α + γ) temperature range exhibited better machinability than as-cast samples. On the other hand, the cutting force was decreased with increasing proeutectoid ferrite fractions. The results also showed that continuity of ausferritic structure along intercellular boundaries plays an important role in determining machinability of austempered ductile iron with different ausferrite volume fractions. Another important result is that higher proeutectoid volume fraction has negative effects on surface roughness.