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incremented and exhibited higher ductility than the fully aus- ferritic ones. In particular, samples with 45% ausferrite and 65% ferrite yielded the best combinations of strength and duc- tility18


(see Table 1). Druschitz et al. 19


of ausferrite was increased, while elongation and toughness exhibited the best values when the intercritical heating was carried out between 1427-1526F (800-830C).


reported that dual phase


ADI (“called machinable austempered cast iron or MADI”) improved strength and ductility when compared to conven- tional DI. The improved strength and ductility is attributable to the microstructure composed of a continuous matrix of equiaxed ferrite with islands of ausferrite.


Valdés et al.21 evaluated the microstructural changes and me-


chanical properties exhibited by DI when it was heat treated in the intercritical interval at different temperatures and then austempered at 707F (375C). The authors indicated that ten- sile strength and yield strength increased when the amount


The authors of this paper have also addressed this topic, analyzing the effect the amount and morphologies of phas- es, austempering temperature and cast part size have on the final microstructure and its properties.16,17


As expected,


as the amount of ausferrite increased, tensile strength and yield stress also increased, while elongation diminished for all the austempering temperatures analyzed. The best com- binations of strength and elongation were found in dual phase ADI microstructures austempered at 662F (350C). For example, the microstructure composed of 35% fer- rite-65% ausferrite combines a tensile strength of 730 MPa


Table 1. Mechanical Properties of Dual Phase ADI Obtained by Different Authors


* The graphite areas were not considered in the percentage of the reported microconstituents. 10 International Journal of Metalcasting/Winter 2012


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