The influence of nodule count on the austempering kinetics of a Mn-Cu ductile iron

Abstract

Austempering kinetic measurements and mechanical property measurements are reported for a Mn-Cu ductile iron containing 0.2%Mn and 0.4% Cu with nodule counts of 100 and 250mm⁻². The austempering treatment consisted of austempering at 290, 340 and 390°C after asutenitising at 900°C. It is shown that increasing the nodule count accelerates the stage I austempering reaction but has little effect on the stage II reaction. This moves the heat treatment processing window to earlier austempering times and increases the temperature at which the window closes. Increasing the nodule count results in a finer and more homogeneous ausferrite structure that increases the strength and ductility of the austempered iron.

Keywords:

• ductile iron
• austempering kinetics nodule count
• mechanical properties