The relationship between austempering parameters, microstructure and mechanical properties in a Mn—Mo—Cu alloyed ductile iron

Measurements of ultimate tensile strength, 0.2% proof strength, elongation and unnotched Charpy impact energy are presented as a function of austempering time in the range from 1 to 4320 minutes for austempering temperatures of 400, 375 and 285 °C and austenitising temperatures of 870, 920 and 950 °C for a ductile iron of composition 3.39%C, 2.56% Si, 0.25% Mo, 0.29% Cu, 0.37% Mn and 0.04% Mg. Austempering kinetic measurements are presented for the various austenitising and austempering temperatures. These measurements are analysed to relate microstructure and mechanical properties and to define processing windows for the different austempering conditions. The analysis suggests a new definition for the closure time of the processing window. The newly defined processing windows are consistent with mechanical property observations in the present iron and a previously studied iron with the same base composition but containing 0.67% Mn.