INFLUENCE OF AUSTENITISING TEMPERATURE ON MECHANICAL-PROPERTIES OF HIGH MANGANESE ALLOYED DUCTILE IRON

The mechanical properties obtainable in a high Mn ductile iron containing 3.52%C, 2.64%Si, 0.67%Mn, 0.007%P, 0.013%S, 0.25%Mo, 0.25%Cu, and 0.04%Mg are defined. Measurements of ultimate tensile strength, 0.2% proof strength, impact energy, and elongation are presented as a function of austempering time in the range 1-4320 min for austempering temperatures of 285 and 375 degrees C and austenitising temperatures of 870, 900, and 920 degrees C. The austempering processing window is shown to be open for the three austenitising temperatures at an austempering temperature of 285 degrees C, and the mechanical properties satisfy the austempered ductile iron (ADI) standard ASTM A897M:1990. Decreasing the austenitising temperature is shown to increase the closure temperature of the processing window, but for the lowest austenitising temperature the window is still closed for an austempering temperature of 375 degrees C. The improvement in ductility obtained by using an austenitising temperature of 870 degrees C is insufficient to satisfy the ADI standard. (C) 1995 The Institute of Materials.