Austempering and Boro-Austempering Treatments in Gray Cast Iron

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Materials Performance and Characterization

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Austempering heat treatment of gray cast iron can significantly improve its mechanical properties. In addition, increasing its surface hardness by means of thermochemical treatments such as boriding can further extend its range of use. In this work, gray cast iron samples with the composition 3.6 % C - 2.1 % Si - 0.43 % Mn - 0.26 % Cr - bal Fe were subjected to austempering treatment using austenitizing at 900°C, with subsequent cooling using austempering salt baths at temperatures of 240°C, 300°C, and 360°C for 1, 2, 3, and 4 hours with subsequent cooling in air. Another set of samples was subjected to boro-austempering treatments, which consisted of boriding at 950°C for 2 to 4 hours in molten borax and followed by cooling in salt baths at temperatures of 240°C, 300°C, and 360°C for 1, 2, 3, and 4 hours, with subsequent air cooling. This approach avoids the need for further heating the work piece to perform the austempering treatment. Subsequently, the samples were characterized for micro-hardness and adhesive wear behavior. The austempering treatment significantly increased material performance, and the boro-austempering treatment further improved its properties.



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