Mechanical Performance of Austempered Ductile Iron.

Plates of Austempered Ductile Iron ADI containing, in mass pct, 3.7 C. 2.7 Si, 0.97 Ni and 0.27 Mn were heat treated to ASTM 897 Grade 1 and 3 tensile properties and subjected to tensile testing at temperatures between -80 and 120 deg C. Room temperature yield and ultimate tensile strengths met specifications but values of elongation were lower than expected. The retained austenite contents contributed to lowered yield strengths during low temperature testing and increased ultimate tensile strengths and ductilities during high temperature testing. These changes in properties were related to the effects of temperature on the strain-induced transformation of austenite to martensite. The lower than expected ductility of the ADI specimens was related to microporosity, differences in graphite nodule distributions, differences in strain hardening related to austenite stability, and the ductile-to-brittle fracture transition of the matrix ferrite with decreasing temperature. Ductile iron, Austempering, Mechanical properties, Austenite transformation.