Stepped austempering heat treatment of a 0-67%Mn-Mo-Cu ductile iron

Measurements of the retained austenite content, average austenite C content, UTS, 0.2% proof strength, elongation, and unnotched Charpy impact energy are reported for the stepped austempering treatment (870°C for 120 min; 375°C for 120 min; 285°C)as a function of austempering time at 285°C for a ductile iron of composition Fe–3.5 C–2.64Si–0.67n–0.007P–0.013S–0.25Mo–0.25Cu–0.04Mg (wt-%). These measurements are compared with previous measurements for single and stepped austempering treatments. The comparison shows that stepped austempering treatments can be used to improve elongation and impact energy obtained in single treatments in the high Mn ductile iron. Control over the austenitising and first step austempering temperatures can be used to change the relative improvements in elongation and impact energy. The austempering time required to achieve these improvements is much longer than that used in a single step treatment.