Influence of austenitising temperature on austempering of an Mn-Mo-Cu alloyed ductile iron Part 2 - Mechanical properties

Abstract

Measurements of ultimate tensile strength, 0.2% proof strength, elongation, and impact energy are presented as afunction of austempering time in the range 1 to 4320 minfor austempering temperatures of 350, 375 and 400°C and austenitising temperatures of 870 and 920°C in a ductile iron of composition Fe-3.49C-2.33Si-0.42Mn-0.25Cu-0.23Mo-O.035Mg. With an austenitising temperature of 920°C, the mechanical properties satisfy the ASTM A897M: 1990 austempered ductile iron (ADI) standard at an austempering temperature of 350°C but not at 375 and 400°C. This is consistent with the predictions from the austempering kinetic measurements of an open processing window at 350°C and a closed window at 375 and 400°C. The mechanical properties measured with an austenitising temperature of 870°C satisfy the standard at 350 and 375°C but not at 400°C. This is consistent with the predictions from austempering kinetic measurements of an open window at 350 and 375°C and a closed window at 400°C. Decreasing the austenitising temperature increases the closure temperature of the processing window and moves it to earlier austempering times and reduces the width of the processing window. Decreasing the austenitising temperature is shown to be afactor to be considered in obtaining the higher ductility grades of the ADI standard.