Effect of Quenching and Partitioning Heat Treatment on Ductile Cast Irons

Abstract

In this study, the ductile cast irons were prepared by the melting process and then carried out the quenching and partitioning heat treatment. The microstructures were observed by both an optical microscopy and a field emission scanning electron microscope and the tensile strengths were measured by a uniaxial tensile tester. The effect of partitioning time on the microstructures and the tensile strength were investigated. The results showed that the matrix of as-cast samples contain about 26% ferrite and 74% pearlite and the microstructure quenched without partitioning consisted of a mixture of graphite nodules plus lath martensite plus retained austenite. With the increase of the partitioning time, the retained austenite became stable and could transform into lower bainite or carbide gradually, which gave rise to the fact that the tensile strength changed nonlinearly and reached a maximum at the partitioning time about 120 minutes.