Morphology of bainitic platelets of austempered ductile iron and their effects on mechanical properties

摘要

It is well known that since there is a quantity of graphite nodules, and high contents of silicon and retained austenite in austempered ductile iron (ADI), the morphology of bainite is different from that of austempered steel [1-4]. An interesting fact is that the comprehensive mechanical properties of lower bainitic steel are favourable, but although the lower bainitic platelets are generally finer than the upper bainitic platelets in ADI, the properties of ADI with lower bainitic austenitic matrix are inferior to those of ADI with upper bainitic austenitic matrix. Through observation of ADI specimens obtained under different conditions by scanning electron microscopy (SEM), we found that the presence of subunits of bainite and variations of morphology play an important role in the mechanical properties of ADI.