Led by Robin Foley

adiThis project focused on understanding the properties and hardenability limits that can be obtained in intercritically austenitized, austempered ductile iron (IADI) as a lightweight and cost effective materials for casting applications.   

The spherical nodules of graphite in ductile cast iron make ductile iron much less brittle than traditional cast iron and allow it to be used as a low cost alternative to steel in some applications.  Austempering is an isothermal heat treatment that was developed to further improve the mechanical properties of ductile iron by transforming the matrix into ausferrite.  UAB recently finished a project studying intercritically austenitized, austempered ductile iron (IADI), which is austenitized at a lower temperature than conventional ADI; the temperature falls in the intercritical range, producing a matrix that consists of a combination of proeutectoid ferrite and ausferrite.  IADI has nearly twice the yield strength and similar elongation as ferritic ductile iron; slightly higher yield and more than double the elongation of pearlitic ductile iron, and lower yield strength but higher elongation than conventional ADI.  

adi2
  SEM secondary electron image showing some of the 
     phases present in an IADI sample alloyed with Mg.
The effects of various composition changes and heat treatments on the structure and properties of ADI and IADI samples were analyzed using optical and SEM microscopy, Brinell hardness testing, and tensile testing.  As part of the project, a comprehensive literature search was also conducted and the results, including numerical data on the effects of composition and heat treatments, were compiled into databases for distribution through the American Foundry Society for the benefit of future ADI researchers and users.