AUSTEMPERING PROCESS IN HIGH MANGANESE ALLOYED DUCTILE CAST-IRON

Microstructural observations and measurements of the retained austenit e content, hardness, austenite C content, and unreacted austenite cont ent are reported during austempering at 400, 375, 320, and 285 degrees C after austenitising at 920 degrees C for a ductile iron containing 3.52%C, 2.64%Si, 0.67%Mn, 0.007%P, 0.013%S, 0.25%Mo, 0.25%Cu, and 0.04 %Mg. The segregation of solute during solidification to the intercellu lar areas is shown to result in the stage I reactions in the eutectic cell and intercellular areas being separated in austempering time. Evi dence is provided of the occurrence of the stage II reaction before th e completion of the stage reaction. The consequence of this sequence o f changes is that she processing window as defined for unalloyed irons and known to correspond to optimum mechanical properties is closed fo r all austempering temperatures.