Study of microstructural evolution and mechanical properties exhibited by non alloyed ductile iron during conventional and stepped austempering heat treatment

It was evaluated the microstructural and mechanical response that a non alloyed ductile iron (DI) presented when was subjected to Conventional Austempering (CA) and Stepped Austempering (SA) heat treatments. X-ray Diffraction (XRD) quantification techniques demonstrated to be the more reliable method for monitoring phase transformations taking place during both CA and SA. When CA was applied some intercellular areas remain untransformed even for long time, however when samples were subjected to SA those untransformed areas disappeared and instead finer ausferrite was found. Additionally mechanical properties values obtained from tensile and impact tests confirmed that for all times used, SA was superior to the CA.

► Conventional (CA) and steeped austempering (SA) were compared in basis of high carbon austenite quantity by 2 methods.
► SA proved to be able to cover with finer ausferrite the untransformed regions in contrast to CA.
► Mechanical properties of SA were superior to CA and fulfilled greatly standard ASTM 897.