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

摘要

Measurements of ultimate tensile strength, 0.2% proof strength, elongation, and impact energy are presented as a function of austempering time in the range 1 to 4320 min for austempering temperatures of 350, 375 and 400 degrees C and austenitising temperatures of 870 and 920 degrees C in a ductile iron of composition Fe-3.49C-2.33Si-0.42Mn-0.25Cu-0.23Mo-0.035Mg. With and austenitising temperature of 920 degrees C, the mechanical properties satisfy the ASTM A897M:1990 austempered ductile iron (ADI) standard at an austempering temperature of 350 degrees C but not at 375 and 400 degrees C. This is consistent with the predictions from the austempering kinetic measurements of an open processing window at 350 degrees C and a closed window at 375 and 400 degrees C. The mechanical properties measured with an austenitising temperature of 870 degrees C satisfy the standard at 350 and 375 degrees C but not at 400 degrees C. This is consistent with the predictions from austempering kinetic measurements of an open window at 350 and 375 degrees C and a closed window at 400 degrees 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 a factor to be considered in obtaining the higher ductility grades of the ADI standard.