Effect of Nickel Element on Processing Window of ADI

摘要

Austempered ductile iron (ADI) is produced via the austempering treatment of ductile iron. In general, an adequate austempering process resulting in the stable ausferritic microstructure and optimal mechanical properties obtained is called processing window. However, processing window mainly depends on lots of factors such as alloying element, cooling rate, austenitizing temperature/time and austempering temperature/time. In this study, 4 wt% nickel (Ni) was added to ductile iron as the experimental material, and then performed a series of austempering treatments consisting of different temperatures (300, 330, 360℃) and times (2, 3, 4, 6 hours). Microstructures of ADI were observed and both the retained austenite and hardness of ADI were also measured, respectively. The purpose is to explore the effect of Ni element on processing window of ADI. The experimental results showed as follows: (1) ADI with 4 wt% Ni possessed the coarse ausferrite and the more amount of retained austenite in the matrix; (2) the processing time was shortened at 300℃ austempering temperature and delayed at 360℃, respectively; (3) the average hardness of ADI was declined.