The Ductile to Brittle Transition Temperature of Unalloyed Adi Material

In material selection, especially in low temperature conditions, one of very important factors it is a ductile to brittle transition temperature, i.e. the temperature when material becomes too brittle to use. In this paper transition temperature determined by impact energy in temperature interval from –196 to +100°C of unalloyed austempered ductile iron with different microstructures have been studied. It was found that transition temperature is influenced by amount of retained austenite, as well as ausferrite morphology. The lowest transition temperature was obtained for ADI material austempered at 350°C for 1 hour, which possesses the most favorable combination of retained austenite volume fraction accompanied with fine acicular appearance of ausferrite. If amount of retained austenite is lower (in case of austempering at 300°C for 1 hour) or morphology is too coarse (after austempering at 400°C for 1 hour) than ductile to brittle transition temperature shifts to higher temperatures.