Abstract
In this study, the effect of boro-tempering heat treatment on the microhardness, impact toughness and microstructure of ductile cast iron has been investigated. Boro-tempering is a heat treatment combining traditional boronizing and austempering processes. Microstructural characterization of the heat treated ductile cast iron was carried out by using optical microscopy, scanning electron microscopy, and X-ray diffraction analysis. The thickness of the boride layer and the hardness change from surface to matrix were measured by the Vickers indentation technique. X-ray diffraction analysis showed that the boride layer formed on the surface of boro-tempered ductile cast iron consisted of dominantly Fe₂B and a small amount of FeB phases. The thickness increased with the boronizing time but was not affected by the cooling rate after the boronizing treatment. It was observed that boro-tempered ductile cast iron has a higher surface hardness and higher impact toughness than that of standard ductile cast iron; it also has a higher surface hardness than that of austempered ductile iron.

Key words
iron alloys, mechanical properties, microstructure, Scanning Electron Microscopy (SEM), boro-tempering

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