Effect of austempering and quenching & partitioning treatments in a CuMnNb ductile cast iron

Ductile cast iron with copper and manganese additions and different niobium contents (0.5%, 1.0% and 2.0%) were submitted to two types of heat treatments: austempering and quenching and partitioning (Q&P). The austenitization temperature was 900 ºC for both treatments. In austempering, samples were cooled directly in salt bath at 240ºC for 1 hour, while in Q&P the samples were salt bath quenched to 170 ºC for 5 minutes , and then partitioned at 240 ºC for 30 and 60 minutes. Microstructural characterization was performed using optical microscopy, Vickers microhardness, X-ray diffraction, microabrasive and microadhesive wear. The samples submitted to the Q&P treatment showed higher hardness compared to the austempered samples due to the presence of martensite in the microstructure.