STEPPED AUSTEMPERING HEAT-TREATMENT OF A 0.67-PERCENT-MN-MO-CU DUCTILE IRON

Measurements of the retained austenite content, aver age austenite C c ontent, UTS, 0.2% proof strength, elongation, and unnotched Charpy imp act energy are reported for the stepped austempering treatment (870 de grees C for 120 min; 375 degrees C for 120 min; 285 degrees C) as a fu nction of austempering time at 285 degrees C for a ductile lion of com position C-2.64Si-0.67Mn-0.007P-0.013S-0.25Mo-0.25Cu-0.04Mg (wt-%). Th ese measurements are compared with previous measurements for single an d stepped austempering treatments. The comparison shows that stepped a ustempering treatments can be used to improve elongation and impact en ergy obtained in single treatments in the high Mn ductile iron. Contro l over the austenitising and first step austempering temperatures can be used to change the relative improvements in elongation and impact e nergy. The austempering time required to achieve these improvements is much longer than that used in a single step treatment.