RELATIONSHIP BETWEEN STRUCTURE AND MECHANICAL-PROPERTIES IN HIGH MANGANESE ALLOYED DUCTILE IRON

Measurements of ultimate tensile strength, 0.2% proof stress, elongation, and impact energy are reported for an alloyed 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, for a range of austempering temperatures and times after austenitising at 920 degrees C for 120 min. It is shown that the mechanical properties satisfy the high strength grades of the standard ASTM A897M:1990, but fail to satisfy the higher ductility grades because of poor ductility. This is attributed to overlapping of the stage I and II reactions and the occurrence of the transformation induced plasticity mechanism during deformation, particularly in irons austempered at higher temperatures.