Influence of heat treatment parameters on stepped austempering of 0.37%Mn-Mo-Cu ductile iron

摘要

Measurements of the average austenite carbon content, retained austenite content, unreacted austenite content, and mechanical properties are reported for various austempering heat treatments of an alloyed ductile iron of composition (wt-%) Fe-3.39C-2.56Si-0.37Mn-0.25Mo-0.29Cu-0.04Mg. It is shown that a stepped austempering treatment can be used to considerably increase the ductility of the alloy compared with a single heat treatment and to extend the austempering time interval over which the ASTM standard can be satisfied. Decreasing the second step austempering temperature accelerates the stage I reaction during the second step treatment but produces little change in the mechanical properties of the alloy used in the present work. Decreasing the first step austempering time to 375 degrees C accelerates the stage I reaction in the second step treatment but slightly decreases the maximum impact energy and increases the austempering time at which it is achieved. (C) 1997 The Institute of Materials.